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Target Review

Hybridization and speciation*

R. Abbott

School of Biology, University of St AndrewsSt Andrews, UK

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D. Albach

Institute of Biology and Environmental Sciences, Carl von Ossietzky‐University OldenburgOldenburg, Germany

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S. Ansell

Natural History MuseumLondon, UK

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J. W. Arntzen

Netherlands Centre for Biodiversity NaturalisRA Leiden, The Netherlands

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N. Bierne

Institut des Sciences de l'Evolution, CNRSMontpellier Cedex 5, France

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J. Boughman

Zoology and BEACON Center for the Study of Evolution in Action, Michigan State UniversityEast Lansing, MI, USA

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A. Brelsford

Department of Ecology and Evolution, University of LausanneLausanne, Switzerland

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C. A. Buerkle

Department of Botany, University of WyomingLaramie, WY, USA

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R. Buggs

School of Biological and Chemical Sciences, Queen Mary University of LondonLondon, UK

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R. K. Butlin

Corresponding Author

Animal and Plant Sciences, The University of SheffieldSheffield, UK

Correspondence: Roger Butlin, Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK.Tel.: +44 114 2220097; fax: +44 114 2220002; e‐mail: E-mail address:r.k.butlin@sheffield.ac.uk
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U. Dieckmann

Evolution and Ecology Program, International Institute for Applied Systems AnalysisLaxenburg, Austria

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F. Eroukhmanoff

Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of OsloOslo, Norway

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A. Grill

Department of Tropical Ecology and Animal Biodiversity, University of ViennaWien, Austria

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S. H. Cahan

Department of Biology, University of VermontBurlington, VT, USA

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J. S. Hermansen

Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of OsloOslo, Norway

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G. Hewitt

School of Biological Sciences, University of East AngliaNorwich, UK

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A. G. Hudson

Department of Biodiversity and Evolutionary Biology, Museo Nacional de Ciencias Naturales (CSIC)Madrid, Spain

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C. Jiggins

Department of Zoology, University of CambridgeCambridge, UK

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J. Jones

Department of Biology, University of KonstanzKonstanz, Germany

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B. Keller

Institute of Systematic Botany, University of ZurichZurich, Switzerland

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T. Marczewski

Royal Botanic Garden EdinburghEdinburgh, UK

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J. Mallet

Genetics, Evolution and Environment, UCLLondon, UK

Organismic and Evolutionary Biology, Harvard UniversityCambridge, MA, USA

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P. Martinez‐Rodriguez

Department of Biology (Genetics), Universidad Autónoma de MadridMadrid, Spain

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M. Möst

EAWAGDübendorf, Switzerland

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S. Mullen

Department of Biology, Boston UniversityBoston, MA, USA

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R. Nichols

School of Biological and Chemical Sciences, Queen Mary University of LondonLondon, UK

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A. W. Nolte

Max‐Planck Institute for Evolutionary BiologyPlön, Germany

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C. Parisod

Laboratory of Evolutionary Botany, Institute of Biology, University of NeuchatelNeuchatel, Switzerland

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K. Pfennig

Department of Biology, University of North CarolinaChapel Hill, NC, USA

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A. M. Rice

Department of Biological Sciences, Lehigh UniversityBethlehem, PA, USA

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M. G. Ritchie

School of Biology, University of St AndrewsSt Andrews, UK

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B. Seifert

Senckenberg Museum of Natural History GoerlitzGoerlitz, Germany

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C. M. Smadja

CNRS Institut des Science de l'Evolution, Université Montpellier 2Montpellier, France

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R. Stelkens

Institute of Integrative Biology, University of LiverpoolLiverpool, UK

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J. M. Szymura

Institute of Zoology, Jagiellonian UniversityKraków, Poland

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R. Väinölä

Finnish Museum of Natural History, University of HelsinkiHelsinki, Finland

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J. B. W. Wolf

Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala UniversityUppsala, Sweden

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D. Zinner

Cognitive Ethology Laboratory, German Primate CenterGöttingen, Germany

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First published: 17 January 2013
Cited by: 576
*

This paper was prepared by the participants of the workshop ‘Hybridization and Speciation’ held at Gregynog Hall, Wales, 23–26 October 2011, and organized by R. K. Butlin, M. G. Ritchie and J. M. Szymura on behalf of the European Science Foundation Network ‘Frontiers in Speciation Research’ (chair: U. Dieckmann). Discussion leaders were: R. Abbott, S. J. E. Baird, N. Bierne, C. A. Buerkle, C. H. Cahan, J. Mallet, A. W. Nolte, C. Parisod and K. Pfennig.

Abstract

Hybridization has many and varied impacts on the process of speciation. Hybridization may slow or reverse differentiation by allowing gene flow and recombination. It may accelerate speciation via adaptive introgression or cause near‐instantaneous speciation by allopolyploidization. It may have multiple effects at different stages and in different spatial contexts within a single speciation event. We offer a perspective on the context and evolutionary significance of hybridization during speciation, highlighting issues of current interest and debate. In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened or broken down due to recombination and gene flow. Theory and empirical evidence suggest the latter is more likely, except within and around strongly selected genomic regions. Hybridization may contribute to speciation through the formation of new hybrid taxa, whereas introgression of a few loci may promote adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic effects and the evolution of selfish genetic material in the genome suggest that the Dobzhansky–Muller model of hybrid incompatibilities requires a broader interpretation. Finally, although the incidence of reinforcement remains uncertain, this and other interactions in areas of sympatry may have knock‐on effects on speciation both within and outside regions of hybridization.

Introduction

If hybridization is defined as reproduction between members of genetically distinct populations (Barton & Hewitt, 1985), producing offspring of mixed ancestry, then it occurs in almost all proposed processes of speciation. The only exceptions would be cases of completely allopatric or instantaneous speciation. Hybridization may cause interactions involving a wide range of types and levels of genetic divergence between the parental forms. This divergence may have accumulated in different ways including neutral divergence, local adaptation and coevolution. Any of these may generate novel phenotypes through interactions in hybrids, including both advantages of transgressive segregation and disadvantages mediated by intrinsic or environmentally mediated incompatibilities. Therefore, the consequences of hybridization and the role it might play in promoting or retarding speciation can be expected to vary widely both between different hybridizing taxa and at different stages of divergence.

Hybridization may occur in many different spatial contexts (Fig. 1). Some of these have been studied intensively, most notably the formation of hybrid zones at abrupt parapatric boundaries (Harrison, 1993) and the exchange of genes between locally adapted populations, such as host races in phytophagous insects (Dres & Mallet, 2002), where there may be no spatial separation at scales above typical dispersal distances. Hybridization may also differ in temporal context, for example, secondary contact after a period of independent evolution vs. continuous contact with divergent selection. Hybridization may follow habitat disturbance, range expansion or both (as in Senecio, Abbott et al., 2003; or baboons, Zinner et al., 2009; for example) and may occur in complex habitat mosaics combining some of the features of hybrid zones with those of local adaptation (as in Louisiana Iris, Arnold et al., 2012; Allonemobius crickets, Ross & Harrison, 2002; or Mytilus bivalves, Bierne et al., 2003).

Speciation is a multi‐level process unfolding through time and space. Populations are subjected to demographic processes and are repeatedly redistributed in space. Novel ecological opportunities can arise, and periods of physical separation will alternate with periods of gene flow. It is quite conceivable that different mechanisms are acting during the different phases of the divergence process. From a genetic perspective, barrier loci that contribute to reduction in gene flow between diverging genomes may, if conditions are right, accumulate gradually, extend or combine their effects until the diverging genomes are eventually sealed off from each other and will not mix any further. Introgression may favour divergence or hybridization may generate new, isolated populations.

Hybridization may be common and widespread, spatially or temporally localized or globally rare. It may influence a rare interacting population much more strongly than an abundant population, and its consequences may depend on whether populations are growing or contracting, local or invasive (Currat et al., 2008). In all cases, the pattern of contemporary hybridization is potentially only a single snapshot of a complex and continuously changing interaction. The evolution of complete reproductive isolation may take hundreds to millions of generations. During this time, populations change in size and spatial distribution, perhaps cyclically due to periodical climate changes (Hewitt, 1996, 2011), and the processes that enhance or erode barriers to gene exchange, including hybridization, may occur at different stages or locations during this extended history (Fig. 1). Although many of the debates concerning outcomes of hybridization refer to specific scenarios, it is important to keep this spatial and temporal context in mind when considering the broad significance of hybridization.

In the context of speciation, hybridization may have several distinct outcomes, which have attracted very different levels of research interest. First, there may be a stable, or at least persistent, balance between selection and hybridization, with only some parts of the genome introgressing between hybridizing populations. This may be true both in tension zones (hybrid zones involving a balance between selection against hybrids and dispersal; Barton & Hewitt, 1985) and in populations adapted to distinct habitats (Nosil et al., 2009). In either case, there may be no progress towards speciation but existing differentiation may be maintained, with the potential for future divergence when circumstances change. Alternatively, barriers to gene exchange may breakdown in such a situation, leading to a reduction or loss of differentiation (e.g. Taylor et al., 2006). The opposite type of outcome involves an increase in the strength of any barriers to gene exchange and a progression towards larger areas of the genome being protected from introgression (Wu, 2001; Via, 2009). This outcome, where hybridization initiates speciation, is that which has probably attracted greatest controversy and therefore is given more attention here. Reinforcement (Servedio & Noor, 2003) is an example of one process that might be involved, where a premating barrier evolves in response to reduced hybrid fitness. Finally, and distinctly, hybridization might contribute to adaptive divergence between populations, and it might also result in the generation of new populations of mixed ancestry that remain distinct from both parental populations (hybrid speciation: Mallet, 2007; Abbott et al., 2010). These new populations may be sexual or asexual, homoploid or polyploid. We do not consider asexual hybrid lineages here, but see Bullini (1994) for a review. Reinforcement and hybrid speciation, in particular, may have subsequent knock‐on effects, facilitating or catalysing further speciation through the differences they generate between populations that are exposed to hybridization and those that are not.

Recent reviews of aspects of speciation (e.g. Fitzpatrick et al., 2009; Nosil et al., 2009; Sobel et al., 2010; Wolf et al., 2010a; Nei & Nozawa, 2011; Smadja & Butlin, 2011) have touched on the role of hybridization in speciation, but none has explicitly dealt with a discussion of the central role of hybridization in species divergence. Here, we recognize that hybridization is widespread, diverse in form and in its potential to contribute to individual speciation events. We focus on identifying key areas of current uncertainty, especially about the circumstances in which the different outcomes introduced above might be more or less likely. We aim to clarify the nature and importance of open questions in these areas and, wherever possible, suggest ways for tackling them. First, we consider alternative outcomes: (i) The development of barriers to gene flow and the factors that promote fission rather than fusion of hybridizing populations and (ii) The contribution that hybridization makes to adaptive divergence and to the origin of new hybrid species. We then discuss the genetic and genomic foundations of these divergent processes, and finally, we look at some of their longer‐term consequences.

Hybridization and the development of genetic barriers to gene flow

Barriers to gene exchange might accumulate during periods when gene flow does not occur due to spatial isolation or physical obstacles to dispersal. However, it is common for populations that have developed incomplete reproductive barriers to be in contact at some stage of divergence, often due to range change, allowing the opportunity for gene flow between them. A critical question in speciation is whether, under these conditions, initial divergence breaks down or barriers to gene flow are enhanced and promote speciation. Theory suggests that this will largely depend on the overall antagonism between selection and recombination among diverging loci (Felsenstein, 1981). For incompletely isolated populations to progress towards speciation, associations among the loci that influence isolation must build up (Smadja & Butlin, 2011). This implies that gene flow is further reduced either at individual barrier loci or across a greater fraction of the genome through associations with these loci (we define ‘barrier loci’ as those under divergent selection or that contribute to reduced hybrid fitness or to assortative mating). Loci that do not contribute to reproductive isolation or are not closely linked to loci that confer some degree of isolation are likely to introgress between hybridizing populations (Barton & Bengtsson, 1986). This raises the important question of what patterns of genomic differentiation we expect to see between diverging taxa: How many genomic regions differentiate during speciation? How small are regions where divergence significantly exceeds the genomic average (sometimes called islands, continents or signatures of divergence in the genome, see Turner et al., 2005; Nosil et al., 2009; Michel et al., 2010)? How are regions of exceptional divergence dispersed around the genome? We suggest that recent discussions of these issues in the context of ecological speciation would benefit from closer attention to well‐established cline theory.

What does cline theory teach us about the development of isolating barriers?

Cline theory provides a framework for understanding the dynamics of reproductive barriers in the face of gene flow. Single‐locus barriers to gene flow are rarely absolute and protect only closely linked loci from introgression. Associations between very many barrier loci, spread across chromosomes and likely to be involved in multiple traits, are required to allow significant portions of the genome to diverge on each side of a consensus cline (Barton & Hewitt, 1985). Recombination will break down these associations, whereas selection limits introgression and maintains them. The strength of associations is therefore determined by the balance between the two, quantified by a coupling coefficient S/R (Barton, 1983; Baird, 1995; Kruuk et al., 1999), in which selection (S), is totalled over barrier loci and recombination (R) is the total map length between barrier loci. High coupling maintains associations and consequently a strong barrier in the long term, favouring independent adaptation despite hybridization. In contrast, with low coupling, barrier loci act independently of one another and are ineffective in keeping populations isolated (Fig. 2a) (Barton, 1983; Baird, 1995).

(a) The outcome of hybridization, leading to fusion of populations or to a stable or increasing barrier to gene exchange, depends on the balance between selection and recombination, which can be expressed as a coupling coefficient, Θ. (b) Spatial coupling of clines. Coupling depends on the genetic architecture of incompatibility selection and on population density and environmental variation. Upper panel: Incompatibility clines can move because of asymmetric fitness effects (one parental genotype is fitter) or because of a gradient in population density. Arrows illustrate this movement as asymmetric‐effective migration rates, with asymmetry due to either demography or selection. Lower panel: Increased coupling in space arises from the tendency of clines to attract one another and then to move together to regions of low population density, environmental transitions or both. The shaded areas illustrate the variation in the environment and population density.

Under certain conditions, barriers to gene flow can be enhanced over time (Navarro & Barton, 2003; Barton & de Cara, 2009). Clines at endogenous barrier loci (where selection results from intrinsic incompatibilities) are not constrained to occur at environmental transitions; they are expected to move towards and coincide in areas of lower population density (Hewitt, 1975; Barton, 1979). Clines can also move and become coincident due to asymmetrical fitness of parental genotypes (Barton & Turelli, 2011). When different endogenous clines meet and overlap, they are expected to become coupled and then these multiple clines move together in space. Such moving tension zones will be trapped by natural barriers to dispersal (Barton, 1979) or will couple with local adaptation clines that are geographically stabilized by selection and therefore become localized (Fig. 2b, Bierne et al., 2011). Spatially coupled barriers increase the number of loci contributing to S at their new joint position, which in turn sharpens clines (Clarke, 1966), increases barrier strength and makes long‐term maintenance of the hybrid zone and of the differentiation between populations more likely (Barton, 1983).

The effect of spatial structure in favouring such a coupling process by generating sufficient linkage disequilibrium to associate unlinked loci when clines overlap has been known for some time (Slatkin, 1975; Endler, 1977; Barton, 1983). Such increases in coupling may be considered steps towards speciation, as they lead to increasingly independent evolutionary trajectories of the taxa on either side of the accumulated barrier. Indeed, spatial coupling is part of a more general phenomenon which includes the build‐up of reproductive barriers through linkage disequilibrium between adaptive and assortative mating loci (Felsenstein, 1981). An analogous process can also operate within a single panmictic population, though requiring some combination of strong selection, tight linkage and multiplicative fitness effects (Barton & de Cara, 2009). A current challenge is to integrate these ideas with those about the strengthening of barriers between locally adapted populations that are an important component of the current ecological speciation literature (e.g. Via, 2009; Feder et al., 2012).

Mechanisms that can enhance coupling

From the theory briefly outlined above, one can think of mechanisms that can catalyse speciation as those that enhance the coupling of a system: (i) mechanisms that reduce recombination (R), (ii) mechanisms that maximize selection at the genome scale (S) and (iii) mechanisms that make clines overlap and prevent their movements, bringing both endogenous and exogenous selection together.

(i) Coupling is more efficiently maintained with reduced recombination, which can arise due to segregating inversions (Noor et al., 2001; Navarro & Barton, 2003; Kirkpatrick & Barton, 2006) or other modifiers of recombination (e.g. genomic divergence due to transposable elements that suppress recombination in hybrids; see below). (ii) Epistasis among barrier loci would lead to higher S than under additivity; gene expression patterns in hybrids can be consistent with this type of epistasis (see below). (iii) Moving clines can be spatially stabilized by physical barriers to dispersal or by local adaptation. All these mechanisms can act independently or in concert to build up genetic barriers. It should be emphasized that the effect of ecologically driven divergent selection is two‐fold: it fuels the populations with divergently selected barrier loci, and it contributes to anchoring, at environmental boundaries, clines for barrier loci that do not interact directly with the environment (endogenous loci, e.g. Dobzhansky–Muller incompatibilities, assortative mating genes; Bierne et al., 2011).

Coupling new ecological adaptations with old intrinsic barriers, an alternative interpretation of seemingly rapid speciation events

Coupling may play a more important role during rapid adaptive population subdivision than is appreciated. The accumulation of intrinsic genetic incompatibilities is often thought to occur too slowly to explain emblematic examples of ecological speciation (e.g. recent host shifts in phytophagous insects or pathogens, Rundle & Nosil, 2005). This is because ecological adaptation has been shown to evolve on a short timescale, even in the absence of geographical isolation, despite the comparatively long waiting time for mutations that could cause incompatibilities between populations to accumulate in appreciable numbers (see Kondrashov, 2003; Gavrilets, 2004). However, coupling theory shows that pre‐existing intrinsic incompatibilities in a tension zone can be recruited to enhance ecological barriers between populations (Bierne et al., 2011). This coupling recruitment process is different from the usual view of reinforcement of premating isolation (Barton & de Cara, 2009). Coupling can build up associations between loci that contribute to any kind of barrier (pre‐ or post‐zygotic, endogenous or exogenous), including pre‐existing barrier loci segregating within one of the populations. This could explain the strikingly deep coalescences often observed at exceptionally differentiated loci between populations in different habitats (Schulte et al., 1997; Pogson, 2001; Colosimo et al., 2005; Wood et al., 2008). Some recent host shifts in phytophagous insects (corn borer, Malausa et al., 2005; maggot fly, Michel et al., 2010) might well result from a new adaptive polymorphism that contributes to the host shift coming into association and coupling with incompatibility loci from a cryptic pre‐existing tension zone. If this is the case, then in these systems ecology should probably not be thought of as the initial catalytic agent of speciation, but rather a subsequent ingredient enhancing further build‐up of reproductive barriers.

New directions in the study of genetic barriers to gene flow

Theory demonstrates that it is possible for multiple barriers to accumulate, or couple, even without spatial isolation. Yet we do not know, either from theory or from accumulated empirical data, whether it is a common evolutionary outcome for reproductive isolation to be enhanced when incompletely isolated populations are in contact. It is unclear to what extent initially divergent populations will become further isolated under conditions of gene flow, stay at the current level of isolation or become less distinct. Evidently, the likelihood of these alternative outcomes will be shaped by the fluctuations in geographical and demographic conditions over time because phylogeographical history strongly influences the nature of the interacting populations and the circumstances of their contact (Hewitt, 2011). The final outcome whereby two species are completely isolated, in the sense that neutral loci are expected to diverge, may occur long after genomically localized divergence was established at multiple, coupled barrier loci. Since introgression and time can easily erase the history of populations at most neutral markers (Grahame et al., 2006; Roberts et al., 2010; Marshall et al., 2011), the history of incipient speciation should ideally be reconstructed using data from barrier loci, accounting for the potential action of selection on these loci (Williamson et al., 2005). A considerable empirical challenge is to move from simply identifying such loci (both endogenous and locally adapted) via analyses of the patterns of genomic divergence (genome scans), QTL mapping or genome‐wide association studies to determining sources of selection, measuring their interactions and inferring their temporal sequence of accumulation.

Although cline theory provides expectations for the behaviour of a high‐dimensional system (populations, evolutionary processes, genomes, time, space, demography, etc., see Fig. 1), it is an ongoing challenge, even with the relative ease of producing genomic data, to connect nucleotide variation to phenotypes of individuals and tie these to the evolutionary dynamics of populations. To understand the build‐up of a genetic barrier, one might capitalize on situations in which associations between the various components of reproductive isolation differ. This can be the case between multiple transects across a single hybrid zone (Szymura & Barton, 1991; Yanchukov et al., 2006; Nolte et al., 2009; Teeter et al., 2010) or replicated combinations of the same lineages at different locations (Riginos & Cunningham, 2005; Butlin et al., 2008; Simard et al., 2009; Bernatchez et al., 2010; Hohenlohe et al., 2010; Caputo et al., 2011). At a larger timescale, the comparison of barriers among multiple taxa with different divergence times can provide insights into the sequential accumulation of barrier loci in a genome (Nadeau et al., 2012). Experimental evolution is an alternative way of studying the accumulation of barrier loci in a controlled environment (Dettman et al., 2007). If known, the number and effects of potential barrier loci and their rates of introgression between populations can provide a basis for analysis. The physical linkage and statistical associations among barrier loci in hybrids are also key to understanding the dynamics of further development of isolating barriers. High‐resolution comparative linkage maps for the divergent populations can indicate whether chromosomal rearrangements are likely to play a role. Likewise, estimates of recombination rates and pairwise associations between putative barrier loci in hybrids and the potential for blocks of ancestry and disequilibria to be retained in hybrids (Baird, 1995) are crucial for understanding the dynamics of progress towards speciation. The theoretical basis of such analyses is best developed for cline theory, but needs to be extended more fully to other geographical scenarios (Fitzpatrick et al., 2009) and to intermittent hybridization.

How often is hybridization a source of adaptive variation that may contribute to speciation?

Incomplete barriers to gene flow retard the exchange of adaptive variation very little. Therefore, one possible outcome of hybridization may be the introgression of selectively favoured alleles from one population into another. This can bring together new adaptive combinations of alleles, which arose in different populations, in much the same way as sexual reproduction within populations leads to the production of combinations of alleles that may provide the basis for adaptive evolution. In this section, we argue that introgression could have important implications for the origin of species.

Consider the following:

  1. Hybridization among species is reasonably common on a per‐species basis, even though usually very rare on a per‐individual basis. About 10–30% of multicellular animal and plant species hybridize regularly. Among those that do hybridize, between 1 in 100 and 1 in 10 000 individuals are hybrids when in sympatry (Mallet, 2005).
  2. Mutations are rare, around 10−8 to 10−9 per generation per base pair. Thus, it is likely to take considerable time for novel adaptations to evolve via mutation and natural selection within a species (depending on the population size).
  3. Hybridization among species can act as an additional, perhaps more abundant, source of adaptive genetic variation than mutation (Grant & Grant, 1994; Kim & Rieseberg, 1999; Arnold & Martin, 2009; Whitney et al., 2010; Kunte et al., 2011). For example, in Darwin's finches, ‘New additive genetic variance introduced by hybridization is estimated to be two to three orders of magnitude greater than that introduced by mutation’ (Grant & Grant, 1994). This process is often referred to as ‘adaptive introgression’ (a somewhat misleading term because, whereas hybridization and introgression can lead to adaptive evolution, the initial hybridization itself is unlikely to be adaptive and is often selected against).
  4. Adaptation is thought to be the most important process driving divergence during speciation (Coyne & Orr, 2004; Sobel et al., 2010; Servedio et al., 2011). Barriers to gene exchange between species, including assortative mating, ecological divergence and Dobzhansky–Muller incompatibilities, can all be driven by adaptation. Assortative mating can be a result of sexual selection, social organization, reinforcement or a by‐product of adaptation to different habitats (Ritchie, 2007; Seifert, 2010; Sobel et al., 2010). Divergence in ecology occurs almost exclusively under selection. Recently characterized Dobzhansky–Muller incompatibilities in Drosophila have been shown to be driven by strong positive selection, although this may not derive from adaptation to the external environment (Orr et al., 2004).
  5. Closely related species tend to hybridize more often. In particular, species in rapidly diversifying adaptive radiations may be particularly prone to hybridization (Price & Bouvier, 2002; Seehausen, 2004; Gourbière & Mallet, 2010).

Taken together, these points suggest that hybridization and introgression, via their role in adaptation, are likely to contribute to speciation, especially in rapidly speciating taxa.

The importance of adaptive introgression in speciation will depend on the nature of adaptive variation. In species with very large populations (e.g. Homo sapiens and Drosophila melanogaster), every possible DNA substitution may arise even within one generation. However, not all species have such large populations, and some classes of adaptive variation may be uncommon even in large populations. Complex adaptations consisting of many genetic changes, for example, will be more rarely encountered than simple mutations. QTL mapping has shown that adaptive traits often consist of multiple loci, spread throughout the genome (McKay & Latta, 2002; Albert et al., 2008). Hybridization has the potential to introduce large sets of new alleles at multiple unlinked loci simultaneously, although strong nonadditive selection may be needed to maintain these sets. Modular, cassette‐like variation (e.g. multiple substitutions in a single gene or a set of linked coding genes and their regulatory elements) (Kim et al., 2008), the components of which have been tested previously by natural selection on their original genetic backgrounds, may be exchanged. In Heliconius, transfer of mimetic patterns across species boundaries requires introgression of complex alleles at multiple loci (Heliconius Genome Consortium, 2012), allowing the rapid acquisition of a genetic architecture that would be difficult to evolve by sequential accumulation of mutations. Repeated introgression is particularly effective in introducing polygenic variation because it will generate multilocus genotypes that remain in transitory linkage disequilibrium, persisting for several generations after each hybridization event.

A large fraction of introgressed variation is likely to be deleterious, and many hybridization events may have no long‐term impact. However, when large numbers of hybridizations occur among closely related species, there is more chance that some will contribute to adaptation and speciation. This is expected to depend very much on ecological opportunity. The existence of opportunities for hybrid populations is seemingly demonstrated by the high frequency of speciation events produced by allopolyploidy in plants (but see below – Allopolyploid Speciation). The abundant genotypes produced by recombination in hybrids should facilitate further exploration of ecological niches different from those of the parents.

Hybridization leading to a new taxon, distinct from both parent species (but with no increase in ploidy), is variously called homoploid hybrid speciation or recombinational speciation (Mallet, 2007; Mavarez & Linarez, 2008; Abbott et al., 2010) (see Fig. 3 and next section). It is usually argued that this process is rare (Rieseberg, 1997), but promotion of adaptive divergence as a result of introgression may be much more common and have the potential to lead to increased reproductive isolation between populations. Therefore, it is critical that these processes are separated, both conceptually and empirically. However, detecting potential adaptive introgression is difficult. It should become easier with new genomic techniques which may show that its frequency has been underestimated in the past. Introgressed genetic variation can enhance the ability to coexist and promote invasiveness (Prentis et al., 2008), and thus help to enlarge the range of a hybrid population substantially. There is likely to be a positive feedback between hybridization and speciation (Seehausen, 2004): hybridization may increase the rate of speciation, and the resulting diversity of closely related species may then provide more opportunities for hybridization. Introgression and hybrid speciation could therefore contribute to the positive feedback of diversity on diversification (Emerson & Kolm, 2005). Systematic tests which conclusively distinguish introgressed alleles from shared polymorphisms are needed, extending beyond cases where there are initial phenotypic clues (such as in butterfly wing patterns) and specifically addressing the role of introgression in adaptive radiation.

Adaptive introgression and hybrid speciation. Divergently selected loci (depicted as black and grey solid lines) in two populations can be combined by recombinant hybridization. The resulting hybrid combination can potentially be adaptive and favoured in a new habitat and can give rise to an independent hybrid taxon (hybrid speciation), or it can allow one population to evolve further, replacing the original genome (adaptive introgression). Globally adaptive variation as well as neutral variation (both depicted as broken lines) can be exchanged between all populations via gene flow through hybridization.

Homoploid hybrid speciation

As mentioned above, one potential outcome of hybridization and admixture is homoploid hybrid speciation, which does not involve ploidy changes in the hybrid (Mallet, 2007; Mavarez & Linarez, 2008; Abbott et al., 2010). A causative, creative role of hybridization is the key feature distinguishing hybrid speciation from neutral admixture of multiple parental genomes. Novel combinations of parental alleles must have contributed to the establishment and persistence of a new population that maintains its distinctness by means of reproductive barriers with both parents. This outcome is what distinguishes hybrid speciation from adaptive introgression. The crucial line of evidence for hybrid speciation is therefore to identify unique hybrid traits that cause isolating barriers, although extensive genomic admixture can also be an important indicator of the process. Helianthus sunflowers are at the highly admixed end of a continuum where the hybrid genomes comprise major contributions from both parental taxa and are now isolated from both parents. In contrast, hybrid speciation in Heliconius butterflies involves adaptive introgression of just one or a few loci that are incorporated into a divergent genetic background and play a direct role in barriers to gene flow (Heliconius Genome Consortium, 2012). In both cases, evidence that hybridization has played a key role was obtained through experimental re‐creation of hybrid phenotypes in the laboratory (Rieseberg et al., 2003; Mavarez et al., 2006). Whereas these systems stand out as hallmark examples, the question arises as to how frequently hybrid speciation occurs and which genotypic and phenotypic signatures remain? Mixed ancestry in the genome of a new taxon is an important signal of hybrid speciation, but it is hard to distinguish from ancestral polymorphism or continued gene exchange and alone is not a sufficient criterion. Admixture measures should ideally be combined with trait‐based studies that connect admixture with the origin of reproductive barriers, such as the identification of alleles underlying specific wing pattern elements in Heliconius (Salazar et al., 2010).

When comparing examples, it is important to consider the ages of the hybrid taxa and whether they are proceeding along divergent evolutionary trajectories in order to separate stages in the process. Analyses of hybrid swarms or young hybrid taxa can play an important role in elucidating the first steps towards hybrid species (Nolte & Tautz, 2010). Although such taxa may not, in the end, give rise to well‐differentiated hybrid species, they can facilitate testing key predictions from models of hybridization and hybrid speciation (Buerkle et al., 2000; Barton, 2001). For example, hybrid populations most likely originate following secondary contact in newly available habitat (after expansion from refugia or artificial introduction) but may be most likely to evolve into hybrid species when a new ecological space is available that is not utilized by the parental taxa. Exogenous selection can then maintain the distinct hybrid taxon even though initial barriers to gene exchange with the parents are not complete. Case studies of recently emerged hybrid taxa, such as Cottus fishes (Stemshorn et al., 2011), Italian sparrows (Passer italiae; Elgvin et al., 2011; Hermansen et al., 2011), Appalachian swallowtail butterflies (Kunte et al., 2011) and Oxford ragwort (Senecio; James & Abbott, 2005; Brennan et al., 2012), show that they remain distinct even though reproductive barriers are not absolute. In Oxford ragwort, the hybrid population has colonized a new environment geographically isolated from those occupied by its parents whereas, in the other three cases, reproductive barriers are sufficient for hybrid taxa to coexist parapatrically (Nolte et al., 2006) or even sympatrically with parental forms (Hermansen et al., 2011; Kunte et al., 2011). Nevertheless, additional evidence should be sought for a direct role of hybrid allelic combinations in barriers to gene flow. Progress in this direction has been made in the analysis of the very recent hybrid origin of Lonicera flies (Rhagoletis mendax × zephyria; Schwarz et al., 2005, 2007), where hybrid traits governing host selection have emerged rapidly and simultaneously caused significant reproductive isolation (allowing the hybrid to persist in sympatry with both parents).

There are numerous study systems in which admixture has occurred at some point in the past. Examples include radiations of fishes such as crater lake cichlids (Schliewen & Klee, 2004), sharpfin silversides (Herder et al., 2006) and the postglacial radiation of whitefishes (Bernatchez, 2004; Hudson et al., 2011). Convincing evidence for ancient admixture has been found in all of these systems, but further evidence is needed for a direct role of hybridization in creating reproductively isolated populations or accelerating diversification. Fixed genomic blocks derived from different parental populations can indicate a hybrid genetic architecture that has evolved because it confers a fitness advantage and creates a reproductive barrier (Fig. 3). Great potential for future studies lies in analyses of the structure of hybrid genomes, particularly the size and distribution of blocks derived from alternative ancestors (Barton, 1983; Baird, 1995). However, fixation of blocks from different parents will also occur through genetic drift (Ungerer et al., 1998; Buerkle & Rieseberg, 2008), and this scenario must be excluded before evidence for hybrid speciation is accepted. Although modelling of the decay of linkage disequilibrium in admixed genomes (Pool & Nielsen, 2009) and the fixation of ancestral blocks (Buerkle & Rieseberg, 2008) have been employed to study hybrid speciation, such methods have yet to be applied to a wide range of hybrid taxa, and further development of these methods is critical. Inferring the evolutionary significance of hybrid genetic architecture in speciation may become more problematic the further back in time the event lies because drift and selection become harder to distinguish.

Together with the age of the hybrid species itself, the level of divergence between the parental taxa is another important consideration for homoploid hybrid speciation studies (as it is for allopolyploid speciation: Paun et al., 2009; Buggs et al., 2009). When divergence is low, there may be little chance of major novelties arising in hybrids but, when divergence is high, intrinsic incompatibility may prevent successful hybridization. Crossing experiments with cichlid fish provide support for more divergent populations being more likely to generate novel trait combinations (Stelkens & Seehausen, 2009). Thus, an important challenge in studies of hybrid speciation is to ask whether there is an ‘optimal’ genetic distance for homoploid hybrid speciation (Arnold et al., 1999; Gross, 2012).

Allopolyploid speciation

Polyploidy, which results in species containing three or more homologous chromosome sets rather than the two in their diploid ancestors, is an important mechanism in hybrid speciation because it creates a strong, though often incomplete, postzygotic reproductive barrier between a hybrid and its parents. While common in only some animals (Mable et al., 2011), polyploidy is of major significance in plant evolution with the latest estimates indicating that all extant flowering plants have polyploidy in their ancestry (Jiao et al., 2011), whereas 15% of angiosperm and 31% of fern speciation events directly involve polyploidy (Wood et al., 2009). Two types of polyploids are normally recognized: autopolyploids in which chromosome sets are derived from the same species and allopolyploids that contain chromosome sets from different species as a consequence of interspecific hybridization. This classification is over‐simplistic (Stebbins, 1971), as it draws a somewhat arbitrary division through a continuum of degrees of divergence between parents involved in crossing and polyploid formation. Allopolyploidy is considered to be more common in nature than autopolyploidy (Coyne & Orr, 2004; although see Soltis et al., 2007), but despite its obvious importance, much remains unknown about the process and its consequences (Soltis et al., 2010). This is particularly true with regard to the establishment of allopolyploid species in the wild.

Well‐established allopolyploid species often occur in habitats where their diploid relatives are not found (Brochmann et al., 2004; Paun et al., 2011). It is feasible, therefore, that ecological divergence is an important driver of allopolyploid establishment, enabling a new allopolyploid species to escape the minority‐type disadvantage resulting from intermating with a parent (Levin, 1975), additional negative effects of interploidal gene flow (Chapman & Abbott, 2010) and possible competitive disadvantages in parental habitats. Determining the role of hybridization per se vs. subsequent ecological selection on the hybrid genotype is important for understanding the relative importance of hybridization vs. selection in the establishment of allopolyploids, as it is for homoploid hybrid populations (see above). Allopolyploids are often geographically widespread, occupying open habitats created by climatic, human or other disturbances (Stebbins, 1984; Brochmann et al., 2004). They frequently exhibit greater vigour and homoeostatic buffering relative to their diploid relatives, making them well suited for colonizing new habitats (Grant, 1981). There are several mechanisms, such as fixed heterozygosity, that may explain the advantages allopolyploids display under such conditions (Levin, 2002; Hegarty & Hiscock, 2007).

The recent finding that many newly formed allopolyploids exhibit considerable genomic and transcriptomic variation relative to their parents (Doyle et al., 2008; Hegarty & Hiscock, 2008) opens the way to examine possible links between the nature of such variation, ecological divergence and speciation (Parisod, 2012). Paun et al. (2011) recently used cDNA‐amplified fragment length polymorphism (cDNA‐AFLP) to examine gene expression differences between two diploid orchid (Dactylorhiza) species and three derivative allotetraploids that differed markedly in ecology, geography and morphology from each other. Certain transcriptomic differences between the five species were correlated with particular eco‐climatic variables, suggesting they could be adaptive. Going beyond association, it will be necessary to demonstrate a direct link between regulatory networks affected by alterations to gene expression and ecological divergence to show that such differences are adaptive. Moreover, it will be necessary to distinguish between the impacts of changes occurring at the time of origin of an allopolyploid and during subsequent evolution on both adaptation and reproductive isolation (Ramsey & Schemske, 2002).

Despite the likely importance of ecological divergence in allopolyploid speciation, there is surprisingly no direct evidence that it originates at the time of origin of an allopolyploid species. This contrasts with the position for homoploid hybrid speciation (Gross & Rieseberg, 2005; Abbott et al., 2010). In seeking experimental evidence to determine whether ecological divergence accompanies or follows allopolyploid speciation, we could focus on the few species known to have originated within the last 100 years or so (Abbott & Lowe, 2004), particularly those that can be resynthesized artificially [e.g. Senecio cambrensis, Tragopogon mirus and T. miscellus (Hegarty et al., 2005; Tate et al., 2009)]. Synthetics of each of these species exhibit considerable genomic and transcriptomic variation relative to their parents, providing a source of novelty on which selection could act (Hegarty et al., 2008; Buggs et al., 2011). Comparisons of fitness between synthetics and parental types transplanted into sites occupied by the wild form of allopolyploid would be one approach to test whether ecological divergence accompanied the origin of these neo‐allopolyploids.

It has been suggested that over the longer term, polyploidy may set the stage for rapid diversification, perhaps even explaining the ‘abominable mystery’ of the origins of angiosperm diversity (De Bodt et al., 2005). Evidence for multiple ancient polyploidization events in the genomes of plants whose chromosomes appear to be diploid seems to favour this view (Blanc et al., 2003; Jiao et al., 2011), as does the frequency of polyploidy in island radiations (Murray & de Lange, 2011) and the theoretical expectation that gene duplication provides raw material for evolution (Lynch & Conery, 2000). However, this view is contradicted by apparently lower diversification rates of polyploids compared to their diploid relatives within genera (Mayrose et al., 2011), and the predictive success of models in which polyploidization is a neutral, one‐way process (Meyers & Levin, 2006; Mayrose et al., 2011). The role of allopolyploidy as a driver of plant diversification thus remains an open question. In neo‐allopolyploids, multiple origins are common (Soltis & Soltis, 1993), forming independent lineages that might merge to generate polyploid populations with high genetic diversity (Soltis & Soltis, 2000; Holloway et al., 2006) or follow independent evolutionary trajectories leading to separate species (Werth & Windham, 1991). The latter has not yet been demonstrated in natural species (Soltis & Soltis, 2009), but patterns of chromosomal change found in independent lineages of the recent allopolyploid Tragopogon miscellus may create incompatibilities that promote speciation (Lim et al., 2008; Chester et al., 2012).

Diverse genetic mechanisms underlie novel phenotypes in hybrids

Hybridization can lead to very different evolutionary outcomes, as discussed above, but what are the genetic mechanisms underlying these alternatives? Hybrid attributes that reduce fitness and those that increase it are generally treated as qualitatively different phenomena (e.g. ‘incompatibilities’ vs. ‘evolutionary novelty’). However, both describe the appearance of potentially fitness‐related phenotypic traits in hybrids that lie outside the parental distributions, be it in fecundity, physiology, morphology or behaviour. The very same genetic mechanisms can underlie novel transgressive phenotypes whether their fitness effects are positive or negative: in both cases, they are due to the creation of genetic combinations that have not been tested by selection in the parental populations. Determining the mechanisms that cause these phenotypes to appear will aid understanding of the impact of hybridization on the speciation process.

Two classes of mechanism might be considered. First, alleles of additive effect may not all be fixed in the same direction between diverging populations, especially if selection is weak (Orr, 1998). Some hybrid genotypes then fall outside the parental distribution (+++− x −−−+ can generate ++++ or −−−−). Second, new phenotypes may result from interactions (dominance or epistasis) between alleles fixed independently in different populations. Dobzhansky–Muller incompatibilities, where these interactions have negative consequences, have dominated research on the genetics of speciation, and the focus has tended to be on simple two‐locus incompatibilities mediated through protein–protein interactions. In fact, both classes of mechanism can be interpreted much more broadly, and the last decade of research has started to reveal a wider variety of genetic mechanisms underlying novel hybrid phenotypes, including genome restructuring, duplication/deletion (Oka's model, see e.g. Nei & Nozawa, 2011), alterations in the timing and levels of gene expression, epigenetic effects and transposon activation (Landry et al., 2007; Doyle et al., 2008; Masly et al., 2006; Michalak, 2009; references in Ainouche & Jenczewski, 2010). Dissecting these mechanisms will help to understand why hybridization sometimes generates new adaptive phenotypes, how incompatibilities accumulate over time and whether incompatibilities are likely to break down or not when exposed to gene flow and recombination.

The proximate causes of extensive phenotypic novelty in hybrids lie in differences between the contributing genomes that, when combined, have novel effects. Divergence in the regulatory architecture of genes may be particularly likely to produce correlated, genome‐wide responses to hybridization and may occur quickly following isolation. The extent of novel expression patterns in the first few generations following hybridization often exceed what can be expected from simple reshuffling of pairwise epistatic interactions (Ranz et al., 2004). In particular, regulatory genes are fast‐evolving (Castillo‐Davis et al., 2004) and evolve in a compensatory fashion within complex networks, increasing the probability of epistatic effects after hybridization (Johnson & Porter, 2000; Birchler & Veitia, 2010) and leading to one‐to‐many or many‐to‐many interactions rather than the classic one‐to‐one Dobzhansky–Muller incompatibilities. Structural variation between species, including chromosomal organization, gene duplication or loss and transposable element distribution, can also produce substantial phenotypic effects and directly impact recombination rate and reproductive compatibility with parental species (Rieseberg, 2001; Nei & Nozawa, 2011). Differences in genome structure may induce further restructuring (with possible phenotypic consequences) after recombination of the hybrid genomes (Gaeta & Pires, 2010).

Divergence in transposable element complements can occur rapidly and can have profound consequences following hybridization. The merging of divergent genomes in F1 hybrids may result in quantitative or qualitative mismatches between interspersed transposable elements and their maternally transmitted siRNA repressors (Comai et al., 2003; Bourc'his & Voinnet, 2010). Such miss‐regulation can induce the activation of specific transposable elements and promote both restructuring and epigenetic re‐patterning throughout the hybrid genome (Parisod et al., 2010). Although massive mobilization of transposable elements inducing mutation bursts may lead to low hybrid fitness in extreme cases (e.g. hybrid dysgenesis in Drosophila; Blumenstiel & Hartl, 2005), more limited reactivation may promote moderate transposition and result in structural polymorphism that suppresses recombination at homologous loci (e.g. recombinationally inert haplotypes in maize; He & Dooner, 2009). Activation of transposable elements induced by hybridization may thus play a pivotal role during speciation by triggering genome‐wide variation in functional genes (e.g. stably altering expression through sequence disruption or epigenetic changes in the vicinity of insertion sites; Hollister et al., 2011) or strongly modifying recombination patterns across the genome, with potential consequences for barriers to gene flow (Ungerer et al., 2006).

These various genetic mechanisms underlying transgressive hybrid phenotypes differ in a number of attributes that may have important implications for the evolutionary dynamics of populations produced through hybridization. Miss‐regulation of gene expression may be expected to produce new phenotypes immediately upon genome merging, perhaps more readily than protein–protein interactions, with further variants emerging over time as recombination produces novel combinations of interacting genetic elements. Accordingly, the emergence of novel variation is likely to be an ongoing process, with different phenotypes being exposed to natural selection over successive generations. Moreover, the mechanisms that change genome structure and those that alter genome functions might be expected to impact different aspects of speciation and to contribute in qualitatively different ways to the evolutionary dynamics of hybridization. Structural changes are expected to contribute primarily to barriers to gene flow, as chromosomal restructuring that restores reproductive function within the hybrid population also likely induces incompatibility with the parental forms (as in allopolyploidy). In contrast, functional changes can have a wide array of effects on every aspect of the phenotype, playing some role in barriers if they reduce fitness (Ortiz‐Barrientos et al., 2007) and being important in generating fitness‐enhancing evolutionary novelty (Ni et al., 2008; Edelist et al., 2009), a critical prerequisite for ecological differentiation and competitive success in incipient hybrid species. Whether there is a predictable shift from fitness enhancement to fitness reduction with increasing divergence between interacting species, as regulatory network differences, transposable elements, etc. begin to exceed the limits of complementarity or rapid recovery in hybrids, is an open question that could profitably be addressed with experimental systems or controlled studies within particular groups. A better understanding of the mechanisms contributing to hybrid phenotypes may help to resolve some areas of disagreement over the role of hybridization in the speciation process. If gene miss‐regulation is indeed a common source of incompatibilities, as is suggested both by classic studies of hybrid unfitness (Wittbrodt et al., 1989) and by more recent work in yeast and Drosophila (Anderson et al., 2010; Araripe et al., 2010; Kao et al., 2010), a network‐based modelling approach that can accommodate the complex patterns of epistasis typical of regulatory networks may perform significantly better than two‐locus models in predicting evolutionary outcomes (e.g. Porter & Johnson, 2002; Palmer & Feldman, 2009; see sections Hybridization and the Development of Genetic Barriers to Gene Flow and Homoploid Hybrid Speciation).

At the molecular level, we still know relatively little about how these mechanisms work outside of model organisms. Gaining insights into the nature of the multiple genetic elements involved in speciation and hybridization, and including more precise analysis of molecular aspects of phenotypic evolution, is an important task that will substantially increase our ability to identify what is occurring when divergent genomes interact. This is becoming more tractable in nonmodel organisms, with the rapid advances in next‐generation sequencing technologies (e.g. Wolf et al., 2010b). Finally, although we are beginning to appreciate the impact of genome changes on phenotypic variation, linking this to fitness remains a critical challenge (Barrett & Hoekstra, 2011). The hypothesis that particular genetic mechanisms influence the outcome of hybridization via their effect on phenotypes has been tested rigorously in very few systems (e.g. Edelist et al., 2009; Tirosh et al., 2009; Groszmann et al., 2011; Arnold et al., 2012). Experimental approaches would be particularly valuable in integrating laboratory results with natural hybridization events.

Consequences of reinforcement

In the sections above, the emphasis has been on hybridization's direct effects on speciation. Hybridization can give rise to new recombinant populations that become divergent enough from other populations to form new species. Alternatively, hybridization may either break down existing barriers or favour the evolution of stronger barriers to gene exchange that might ultimately finalize speciation. Yet, as we describe below, hybridization can play an additional, indirect role in speciation, by setting the stage for new speciation events.

Given selection against unfit hybrids, traits that generate enhanced prezygotic isolation could evolve where populations are in contact (i.e. reinforcement may occur; Dobzhansky, 1940). Although extensively debated and often controversial, recent theoretical and empirical work indicates that reinforcement can generate increased prezygotic isolation (Servedio & Noor, 2003; Coyne & Orr, 2004), but may not complete speciation (e.g. Bímová et al., 2011). Continued work is still needed to assess its overall contribution to speciation, its frequency and when it is likely to result in complete isolation. Here, we evaluate possible indirect consequences of reinforcement. Reinforcement may result in divergence between populations inside and outside zones of contact with an interacting taxon, leading to three possible outcomes.

First, consider two incompletely isolated taxa, A and B, with partial range overlap. Because hybrids have reduced fitness, reinforcement may lead to divergence between A and B in the region of overlap. The extent of divergence between A and B will depend in part on gene flow into the region of overlap (sympatry) from populations outside the area of overlap (allopatry), where mating traits are under different selection pressures. At the same time, gene flow out from the overlap populations may cause divergent phenotypes to spread into the regions of each taxon where they do not overlap. The balance between these effects can produce an inverse cline (Antonovics, 2006 and references therein; Bímová et al., 2011). Simple models suggest that the leakage of traits that evolve within the hybrid zones into allopatric populations will only be local (Caisse & Antonovics, 1978; Sanderson, 1989) unless driven by an additional form of selection. Reinforcement within the hybrid zone might stall, rather than increase further, if the build‐up of linkage disequilibrium is counteracted by gene flow or recombination from nonselected individuals outside the zone (e.g. Bímová et al., 2011; see reviews by Servedio & Noor, 2003; Coyne & Orr, 2004). Consequently, the degree to which reinforcement drives divergence between populations inside and outside the hybrid zone within taxon A or B depends on (i) the extent to which reinforcement drives divergence between A and B in the first place within the area of overlap, (ii) the extent of gene flow from overlap populations into the remainder of the distributions of A and B and (iii) other selection pressures operating on traits that influence assortment. The balance of these factors may mean that reinforcement results in little or no divergence between the taxa, or among populations within the taxa.

If gene flow within taxon A (or B) is limited, for example in a patchy environment, a second outcome of reinforcement may be the evolution of reproductive traits in overlap populations that are so divergent from those outside the area of contact that individuals with the alternative trait types are less likely to reproduce (Howard, 1993; see also reviews, discussion, and references therein by Pfennig & Pfennig, 2009, 2010; Ortiz‐Barrientos et al., 2009; Hoskin & Higgie, 2010). Consequently, this can lead to the initiation of reproductive isolation between sympatric and allopatric populations of taxon A (or B), which can ultimately lead to speciation (Howard, 1993; Pfennig & Pfennig, 2009, 2010; Ortiz‐Barrientos et al., 2009; Hoskin & Higgie, 2010; for theoretical treatments see Pfennig & Ryan, 2006; McPeek & Gavrilets, 2006). For example, Jaenike et al. (2006) showed that, between two sympatric species of Drosophila, strong hybrid inviability not only selected for discrimination against heterospecifics but also, as a side product, led to discrimination against conspecifics from allopatric populations. Similarly, Svensson et al. (2006) found that strong divergent sexual selection was accompanied by a significant decrease in female matings with conspecifics from other populations. Trade‐offs in fitness between assortative mating and sexual selection within populations may enhance the divergence between populations (e.g. Pfennig & Pfennig, 2005; for further discussion, see Pfennig & Pfennig, 2009, 2010; Ortiz‐Barrientos et al., 2009; Hoskin & Higgie, 2010). These trade‐offs may be emphasized when a stepwise change in environmental conditions coincides with the boundary of the region of range overlap. Other factors that favour reinforcement in the first place (e.g. strong selection, linkage between fitness and mating traits) may also foster divergence between overlap and allopatric populations, underscoring the potential for reinforcement‐mediated speciation to be autocatalytic in nature.

A third possibility occurs where taxa A and B have multiple independent areas of overlap. If traits evolve differently in response to a given heterospecific among geographically distinct overlap populations, or if a given species encounters and undergoes reinforcement differently with several distinct species across its range, such conspecific populations may become reproductively isolated from one another (Howard, 1993; Pfennig & Pfennig, 2009; Hoskin & Higgie, 2010; e.g. Hoskin et al., 2005; Lemmon, 2009). Such diversity in the outcome of reinforcement is especially likely when reinforcement may operate on a multitude of traits (McPeek & Gavrilets, 2006; Pfennig & Ryan, 2006; Lemmon, 2009). As an example of the former scenario, Hoskin et al. (2005) found that premating isolation between two different populations of rainforest tree frogs resulted from unequal divergence in mate preferences in their separate contact zones with an alternative tree frog population.

Evaluating these possibilities is both an empirical and a theoretical challenge. How often do the relevant circumstances arise that lead to these outcomes? How likely are the various types of divergence to persist in the face of gene flow and thereby ultimately result in new species? How likely is gene flow between overlap and nonoverlap regions, particularly where they are ecologically distinct? To answer these questions, comparisons of reproductive traits are needed among populations as well as between taxa. Of particular value are data that: (i) identify the reproductive traits and trait values that are differentially favoured within and outside the range overlap; (ii) measure fitness consequences of trait variation in both regions to identify sources of selective trade‐offs, if any; (iii) evaluate whether trait divergence impacts reproductive success and (iv) determine whether increased genetic differentiation has evolved between regions, independent of the direct effects of hybridization (for a similar set of criteria, see Hoskin & Higgie, 2010). Regarding the last goal, it is important to note that divergence may sometimes be detected using neutral markers (e.g. Svensson et al., 2004; Rice & Pfennig, 2010), but not always (e.g. Hoskin et al., 2005; Jaenike et al., 2006; Thibert‐Plante & Hendry, 2009; see also Hoskin & Higgie, 2010). In addition to empirical studies, theoretical work would be useful for addressing these issues. Finally, future work should incorporate an explicit consideration of other sources of divergent selection that could drive similar patterns and therefore be mistaken for population divergence that arises indirectly from reinforcement (sensu Rundle & Schluter, 1998; see also Coyne & Orr, 2004; Pfennig & Pfennig, 2009; cf. Hoskin & Higgie, 2010). For example, ecological factors (e.g. resource competition, abiotic conditions) differing between overlap and nonoverlap regions may be as important for population differentiation as selection driven by hybridization avoidance (e.g. Etges et al., 2009; see also Price, 1998; Coyne & Orr, 2004; Rundle & Nosil, 2005; Price, 2008; Sobel et al., 2010; Pfennig & Pfennig, 2010; Hoskin & Higgie, 2010 and references therein).

The ideas above are not new (see, for example, Howard, 1993; Price, 1998; and references above), but they have received relatively little investigation, possibly because attention has focused on the process of reinforcement itself. Our goal here is to highlight the need to extend consideration of reinforcement to include its consequences. Moreover, this discussion reflects one of our original points: that hybridization between two populations typically occurs in a complex spatial and temporal context. The outcomes of interactions in different parts of the range of a species may vary, depending on both the environmental and the genetic conditions locally. This creates divergence but the net effect is hard to predict: hybridization may accelerate diversification, as described above for both the case of reinforcement and the case of adaptive introgression, but it need not. More empirical evidence is required.

Concluding remarks

Historically, hybridization has been viewed primarily as a countervailing process to speciation. Secondary contact zones with extensive gene flow may remain stable for thousands of generations, and much of the genome of the interacting species may become mixed. Nevertheless, variation distinguishing the populations is usually maintained and may be built upon or recruited through coupling with other barriers to gene flow. This may also set the scene for reinforcement, and barriers to gene exchange may become stronger and more widespread genomically. Alternatively, populations may fuse. As highlighted above, the factors determining these different outcomes remain poorly understood. Hybridization can also play a more diverse role in promoting speciation. It may provide the raw material for adaptive divergence or initiate new hybrid populations, potentially leading to speciation. Again, the impact of factors such as existing levels of divergence and ecological opportunity on these outcomes requires further study. Both reinforcement and hybrid speciation may generate positive feedback that accelerates diversification. The genomic signatures of hybridization and introgression will be investigated (theoretically and empirically) more fully now that the incidence of hybridization during speciation is better appreciated. However, it is striking that, after so much study, we are still poorly equipped to tackle a fundamental problem such as how to estimate the proportion of hybridization events that have led to speciation, and we cannot yet predict whether a hybridization event will be favourable to speciation or not. In the mid‐20th century, Edgar Anderson was the greatest proponent of the importance of hybridization in evolution (Anderson, 1949; Anderson & Stebbins, 1954), which led to light‐hearted ridicule by some colleagues. As Warren H. Wagner (relayed by Michael Arnold, pers. comm.) once said, ‘We used to make fun of Edgar Anderson by saying that he was finding hybrids under every bush. Then we realized that even the bushes were hybrids’. With genomic tools, we are beginning to understand that the evolutionary importance of hybridization may even exceed Anderson's expectation.

Acknowledgments

We are grateful to the European Science Foundation for funding the Frontiers in Speciation Research network, including this workshop, to Angela Wright for administrative support and to the staff of Gregynog Hall for their excellent hospitality. This is publication ISEM 2012‐127.

    Number of times cited: 576

    • , The Rate of Evolution of Postmating-Prezygotic Reproductive Isolation in Drosophila, Molecular Biology and Evolution, 10.1093/molbev/msx271, 35, 2, (312-334), (2017).
    • , How much do we know about the frequency of hybridisation and polyploidy in the Mediterranean region?, Plant Biology, 20, S1, (21-37), (2017).
    • , Niche divergence of two closely related Carbula species (Insecta: Hemiptera: Pentatomidae) despite the presence of a hybrid zone, Ecological Entomology, 43, 2, (204-214), (2017).
    • , Natural hybridization and genetic and morphological variation between two epiphytic bromeliads, AoB PLANTS, 10, 1, (2018).
    • , Can mesophotic reefs replenish shallow reefs? Reduced coral reproductive performance casts a doubt, Ecology, 99, 2, (421-437), (2018).
    • , Coupling molecular data and experimental crosses sheds light about species delineation: a case study with the genus Ciona, Scientific Reports, 10.1038/s41598-018-19811-2, 8, 1, (2018).
    • , Rapid allopolyploid radiation of moonwort ferns ( Botrychium ; Ophioglossaceae) revealed by PacBio sequencing of homologous and homeologous nuclear regions, Molecular Phylogenetics and Evolution, 10.1016/j.ympev.2017.11.025, 120, (342-353), (2018).
    • , Detecting hybridization by likelihood calculation of gene tree extra lineages given explicit models, Methods in Ecology and Evolution, 9, 1, (121-133), (2017).
    • , What do we mean when we talk about hybrid speciation?, Heredity, (2018).
    • , Variation and constraints in hybrid genome formation, Nature Ecology & Evolution, (2018).
    • , Introgressive hybridization between the Atlantic and Pacific herring (Clupea harengus and Clupea pallasii) in the White Sea, Barents and Kara Seas evidenced by microsatellites, Conservation Genetics, 10.1007/s10592-017-1036-5, 19, 1, (143-153), (2017).
    • , Impacts of taxonomic inertia for the conservation of African ungulate diversity: an overview, Biological Reviews, 93, 1, (115-130), (2017).
    • , Genetic and morphological discrimination of three species of ninespined stickleback Pungitius spp. (Teleostei, Gasterosteidae) in France with the revalidation of Pungitius vulgaris (Mauduyt, 1848), Journal of Zoological Systematics and Evolutionary Research, 56, 1, (77-101), (2017).
    • , Genomic data reveal cryptic lineage diversification and introgression in Californian golden cup oaks (section Protobalanus), New Phytologist, 218, 2, (804-818), (2017).
    • , Size‐assortative choice and mate availability influences hybridization between red wolves (Canis rufus) and coyotes (Canis latrans), Ecology and Evolution, 8, 8, (3927-3940), (2018).
    • , Low levels of hybridization in two species of African driver ants, Journal of Evolutionary Biology, 31, 4, (556-571), (2018).
    • , The role of mate‐choice copying in speciation and hybridization, Biological Reviews, 93, 2, (1304-1322), (2018).
    • , A comparative study of growth: different body weight trajectories in three species of the genus Eublepharis and their hybrids, Scientific Reports, 8, 1, (2018).
    • , Craniomandibular form and body size variation of first generation mouse hybrids: A model for hominin hybridization, Journal of Human Evolution, 116, (57), (2018).
    • , Hybrid chickadees are deficient in learning and memory, Evolution, 72, 5, (1155-1164), (2018).
    • , Hybrid speciation leads to novel male secondary sexual ornamentation of an Amazonian bird, Proceedings of the National Academy of Sciences, 115, 2, (E218), (2018).
    • , Hybridization can promote adaptive radiation by means of transgressive segregation, Ecology Letters, 21, 2, (264-274), (2017).
    • , Factors promoting polyploid persistence and diversification and limiting diploid speciation during the K–Pg interlude, Current Opinion in Plant Biology, 42, (1), (2018).
    • , Characterization of sympatric Platanthera bifolia and Platanthera chlorantha (Orchidaceae) populations with intermediate plants, PeerJ, 6, (e4256), (2018).
    • , Evolutionary dynamism in bryophytes: Phylogenomic inferences confirm rapid radiation in the moss family Funariaceae, Molecular Phylogenetics and Evolution, 120, (240), (2018).
    • , Sexual conflict and ecology: Species composition and male density interact to reduce male mating harassment and increase female survival, Evolution, 72, 4, (906-915), (2018).
    • , Scale and direction of adaptive introgression between black cottonwood (Populus trichocarpa) and balsam poplar (P. balsamifera), Molecular Ecology, 27, 7, (1667-1680), (2018).
    • , Sympatric serpentine endemic Monardella (Lamiaceae) species maintain habitat differences despite hybridization, Molecular Ecology, 27, 9, (2302-2316), (2018).
    • , Chloroplastic and nuclear diversity of wild beets at a large geographical scale: Insights into the evolutionary history of the Beta section, Ecology and Evolution, 8, 5, (2890-2900), (2018).
    • , New prospects in the detection and comparative analysis of hybridization in the tree of life, American Journal of Botany, 105, 3, (364-375), (2018).
    • , The breakdown of genomic ancestry blocks in hybrid lineages given a finite number of recombination sites, Evolution, 72, 4, (735-750), (2018).
    • , Genetic structuring and secondary contact in the white‐chested Amazilia hummingbird species complex, Journal of Avian Biology, 49, 4, (2018).
    • , Identification of a novel interspecific hybrid yeast from a metagenomic spontaneously inoculated beer sample using Hi‐C, Yeast, 35, 1, (71-84), (2017).
    • , Ecological and Genetic Divergences with Gene Flow of Two Sister Species (Leucomeris decora and Nouelia insignis) Driving by Climatic Transition in Southwest China, Frontiers in Plant Science, 9, (2018).
    • , Phylogeography of Orinus (Poaceae), a dominant grass genus on the Qinghai-Tibet Plateau, Botanical Journal of the Linnean Society, 186, 2, (202), (2018).
    • , Genome‐wide single‐nucleotide polymorphism data reveal cryptic species within cryptic freshwater snail species—The case of the Ancylus fluviatilis species complex, Ecology and Evolution, 8, 2, (1063-1072), (2017).
    • , Small-scale intraspecific patterns of adaptive immunogenetic polymorphisms and neutral variation in Lake Superior lake trout, Immunogenetics, 70, 1, (53), (2018).
    • , Possible glimpses into early speciation: the effect of ovarian fluid on sperm velocity accords with post‐copulatory isolation between two guppy populations, Journal of Evolutionary Biology, 31, 1, (66-74), (2017).
    • , Hybridization could be a common phenomenon within the highly diverse lizard genus Liolaemus, Journal of Evolutionary Biology, 31, 6, (893-903), (2018).
    • , Interspecific competition promotes habitat and morphological divergence in a secondary contact zone between two hybridizing songbirds, Journal of Evolutionary Biology, 31, 6, (914-923), (2018).
    • , Inferring the demographic history underlying parallel genomic divergence among pairs of parasitic and nonparasitic lamprey ecotypes, Molecular Ecology, 26, 1, (142-162), (2016).
    • , Geographic cline analysis as a tool for studying genome‐wide variation: a case study of pollinator‐mediated divergence in a monkeyflower, Molecular Ecology, 26, 1, (107-122), (2016).
    • , Demographic modelling with whole‐genome data reveals parallel origin of similar Pundamilia cichlid species after hybridization, Molecular Ecology, 26, 1, (123-141), (2016).
    • , Stabilization of a salamander moving hybrid zone, Ecology and Evolution, 7, 2, (689-696), (2016).
    • , Demographic and spatial determinants of hybridization rate, Journal of Ecology, 105, 1, (29-38), (2016).
    • , Adaptive evolution and segregating load contribute to the genomic landscape of divergence in two tree species connected by episodic gene flow, Molecular Ecology, 26, 1, (59-76), (2016).
    • , Benefits from living together? Clades whose species use similar habitats may persist as a result of eco‐evolutionary feedbacks, New Phytologist, 213, 1, (66-82), (2016).
    • , Impacts of human‐induced environmental disturbances on hybridization between two ecologically differentiated Californian oak species, New Phytologist, 213, 2, (942-955), (2016).
    • , Combining hydrodynamic modelling with genetics: can passive larval drift shape the genetic structure of Baltic Mytilus populations?, Molecular Ecology, 26, 10, (2765-2782), (2017).
    • , Molecular ecology studies of species radiations: current research gaps, opportunities and challenges, Molecular Ecology, 26, 10, (2608-2622), (2017).
    • , Phylogeography of the sergeants Abudefduf sexfasciatus and A. vaigiensis reveals complex introgression patterns between two widespread and sympatric Indo‐West Pacific reef fishes, Molecular Ecology, 26, 9, (2527-2542), (2017).
    • , Island floras as model systems for studies of plant speciation: Prospects and challenges, Journal of Systematics and Evolution, 55, 1, (1-15), (2017).
    • , Targeted re‐sequencing confirms the importance of chemosensory genes in aphid host race differentiation, Molecular Ecology, 26, 1, (43-58), (2016).
    • , Phylogenetic relationships in Kerkia and introgression between Hauffenia and Kerkia (Caenogastropoda: Hydrobiidae), Journal of Zoological Systematics and Evolutionary Research, 55, 2, (106-117), (2016).
    • , A genomic footprint of hybrid zone movement in crested newts, Evolution Letters, 1, 2, (93-101), (2017).
    • , Characterizing divergence through three adjacent Australian avian transition zones, Journal of Biogeography, 44, 10, (2247-2258), (2017).
    • , Copy number increases of transposable elements and protein‐coding genes in an invasive fish of hybrid origin, Molecular Ecology, 26, 18, (4712-4724), (2017).
    • , Jumping genes: Genomic ballast or powerhouse of biological diversification, Molecular Ecology, 26, 18, (4587-4590), (2017).
    • , Geographic variation in hybridization across a reinforcement contact zone of chorus frogs (Pseudacris), Ecology and Evolution, 7, 22, (9485-9502), (2017).
    • , Hybrid zone formation and contrasting outcomes of secondary contact over transects in common toads, Molecular Ecology, 26, 20, (5663-5675), (2017).
    • , Genomic variation across two barn swallow hybrid zones reveals traits associated with divergence in sympatry and allopatry, Molecular Ecology, 26, 20, (5676-5691), (2017).
    • , Hybridization between ecotypes in a phenotypically and ecologically heterogeneous population of Iris savannarum (Iridaceae) in Florida, Plant Species Biology, 32, 4, (309-322), (2017).
    • , Topology of syngameons, Ecology and Evolution, 7, 24, (10486-10491), (2017).
    • , Synergistic selection between ecological niche and mate preference primes diversification, Evolution, 71, 1, (6-22), (2016).
    • , parallelnewhybrid: an R package for the parallelization of hybrid detection using newhybrids, Molecular Ecology Resources, 17, 1, (91-95), (2016).
    • , Hybridisation and lack of prezygotic barriers between Phymata pennsylvanica and americana, Ecological Entomology, 42, 2, (210-220), (2017).
    • , Climatic effects on population declines of a rare wetland species and the role of spatial and temporal isolation as barriers to hybridization, Functional Ecology, 31, 6, (1262-1274), (2017).
    • , Biogeography predicts macro‐evolutionary patterning of gestural display complexity in a passerine family, Evolution, 71, 5, (1406-1416), (2017).
    • , Asymmetry matters: A genomic assessment of directional biases in gene flow between hybridizing spruces, Ecology and Evolution, 7, 11, (3883-3893), (2017).
    • , Incipient ecological speciation between successional varieties of a dominant tree involves intrinsic postzygotic isolating barriers, Ecology and Evolution, 7, 8, (2501-2512), (2017).
    • , Two's company, three's a crowd: new insights on spruce budworm species boundaries using genotyping‐by‐sequencing in an integrative species assessment (Lepidoptera: Tortricidae), Systematic Entomology, 42, 2, (317-328), (2016).
    • , Unexpected hybridization patterns in Near Eastern terrapins (Mauremys caspica, M. rivulata) indicate ancient gene flow across the Fertile Crescent, Zoologica Scripta, 46, 4, (401-413), (2016).
    • , Maintaining genetic integrity of coexisting wild and domestic populations: Genetic differentiation between wild and domestic Rangifer with long traditions of intentional interbreeding, Ecology and Evolution, 7, 17, (6790-6802), (2017).
    • , Genetic differentiation and inferred dynamics of a hybrid zone between Northern Spotted Owls (Strix occidentalis caurina) and California Spotted Owls (S. o. occidentalis) in northern California, Ecology and Evolution, 7, 17, (6871-6883), (2017).
    • , Genomewide patterns of variation in genetic diversity are shared among populations, species and higher‐order taxa, Molecular Ecology, 26, 16, (4284-4295), (2017).
    • , Segmental allotetraploidy generates extensive homoeologous expression rewiring and phenotypic diversity at the population level in rice, Molecular Ecology, 26, 20, (5451-5466), (2017).
    • , Widespread hybridization and bidirectional introgression in sympatric species of coral reef fish, Molecular Ecology, 26, 20, (5692-5704), (2017).
    • , Interpreting the genomic landscape of speciation: a road map for finding barriers to gene flow, Journal of Evolutionary Biology, 30, 8, (1450-1477), (2017).
    • , Distinct sources of gene flow produce contrasting population genetic dynamics at different range boundaries of a Choristoneura budworm, Molecular Ecology, 26, 23, (6666-6684), (2017).
    • , Effects of assortative mate choice on the genomic and morphological structure of a hybrid zone between two bird subspecies, Molecular Ecology, 26, 22, (6430-6444), (2017).
    • , Genetic and morphometric data demonstrate alternative consequences of secondary contact in Clitarchus stick insects, Journal of Biogeography, 44, 9, (2069-2081), (2017).
    • , Genomewide analysis of admixture and adaptation in the Africanized honeybee, Molecular Ecology, 26, 14, (3603-3617), (2017).
    • , Widespread hybridization within mound‐building wood ants in Southern Finland results in cytonuclear mismatches and potential for sex‐specific hybrid breakdown, Molecular Ecology, 26, 15, (4013-4026), (2017).
    • , Quantification of the zygotic barrier between interbreeding taxa using gene flow data, Oikos, 126, 7, (948-958), (2016).
    • , Natural hybridization and reproductive isolation between two Primula species, Journal of Integrative Plant Biology, 59, 8, (526-530), (2017).
    • , Neo‐ and Paleopolyploidy contribute to the species diversity of Asplenium—the most species‐rich genus of ferns, Journal of Systematics and Evolution, 55, 4, (353-364), (2017).
    • , Allopatric divergence and secondary contact without genetic admixture for richanna perimelaina (Lepidoptera: Geometridae), an alpine moth endemic to the Hengduan Mountains, Systematic Entomology, 42, 4, (703-713), (2017).
    • , Allopatric speciation despite historical gene flow: Divergence and hybridization in Carex furva and C. lucennoiberica (Cyperaceae) inferred from plastid and nuclear RAD‐seq data, Molecular Ecology, 26, 20, (5646-5662), (2017).
    • , Plant speciation across environmental gradients and the occurrence and nature of hybrid zones, Journal of Systematics and Evolution, 55, 4, (238-258), (2017).
    • , hybriddetective: A workflow and package to facilitate the detection of hybridization using genomic data in r, Molecular Ecology Resources, 17, 6, (e275-e284), (2017).
    • , History rather than hybridization determines population structure and adaptation in Populus balsamifera, Journal of Evolutionary Biology, 30, 11, (2044-2058), (2017).
    • , The evolution of the Cercopithecini: a (post)modern synthesis, Evolutionary Anthropology: Issues, News, and Reviews, 26, 6, (336-349), (2017).
    • , Digest: Chemical communication and sexual selection in lizards*, Evolution, 71, 10, (2535-2536), (2017).
    • , Species boundaries in the human pathogen Paracoccidioides, Fungal Genetics and Biology, 106, (9), (2017).
    • , Temporal change of the Baltic Sea–North Sea blue mussel hybrid zone over two decades, Marine Biology, 164, 11, (2017).
    • , Male-driven reproductive and agonistic character displacement in darters and its implications for speciation in allopatry, Current Zoology, (2017).
    • , Requirement of Whole-Genome Sequencing, The Common Bean Genome, 10.1007/978-3-319-63526-2_5, (109-128), (2017).
    • , Speciation, Process of ☆, Reference Module in Life Sciences, 10.1016/B978-0-12-809633-8.02366-9, (2017).
    • , The genomic mosaicism of hybrid speciation, Science Advances, 3, 6, (e1602996), (2017).
    • , Hox genes reveal genomic DNA variation in tetraploid hybrids derived from Carassius auratus red var. (female) × Megalobrama amblycephala (male), BMC Genetics, 18, 1, (2017).
    • , Patterns of parasite distribution in the hybrids of non-congeneric cyprinid fish species: is asymmetry in parasite infection the result of limited coadaptation?, International Journal for Parasitology, 47, 8, (471), (2017).
    • , Genomic evidence of hybridization between two independent invasions of European green crab (Carcinus maenas) in the Northwest Atlantic, Heredity, 119, 3, (154), (2017).
    • , A tipping point in parapatric speciation, Journal of Theoretical Biology, 421, (81), (2017).
    • , Temporal shifts in the saltmarsh–Nelson’s sparrow hybrid zone revealed by replicated demographic and genetic surveys, Conservation Genetics, 18, 2, (453), (2017).
    • , Loss of Heterozygosity Drives Adaptation in Hybrid Yeast, Molecular Biology and Evolution, 34, 7, (1596), (2017).
    • , Making sense of genomic islands of differentiation in light of speciation, Nature Reviews Genetics, 18, 2, (87), (2017).
    • , Altered chromatin compaction and histone methylation drive non-additive gene expression in an interspecific Arabidopsis hybrid, Genome Biology, 18, 1, (2017).
    • , Hybrids and horizontal transfer: introgression allows adaptive allele discovery, Journal of Experimental Botany, 10.1093/jxb/erx297, 68, 20, (5453-5470), (2017).
    • , Asymmetrical natural hybridization varies among hybrid swarms between two diploid Rhododendron species, Annals of Botany, 120, 1, (51), (2017).
    • , Hybridization success is largely limited to homoploid Prunus hybrids: a multidisciplinary approach, Plant Systematics and Evolution, 303, 4, (481), (2017).
    • , Island ontogenies, syngameons, and the origins and evolution of genetic diversity in the Canarian endemic flora, Perspectives in Plant Ecology, Evolution and Systematics, 10.1016/j.ppees.2017.03.003, 27, (9-22), (2017).
    • , Is homoploid hybrid speciation that rare? An empiricist’s view, Heredity, 118, 6, (513), (2017).
    • , Inconsistency between morphological traits and ancestry of individuals in the hybrid zone between two Rhododendron japonoheptamerum varieties revealed by a genotyping-by-sequencing approach, Tree Genetics & Genomes, 13, 1, (2017).
    • , Effects of interspecific gene flow on the phenotypic variance–covariance matrix in Lake Victoria Cichlids, Hydrobiologia, 791, 1, (145), (2017).
    • , Contrasting molecular and morphological evidence for the identification of an anomalousButeo: a cautionary tale for hybrid diagnosis, PeerJ, 5, (e2850), (2017).
    • , Importance of incomplete lineage sorting and introgression in the origin of shared genetic variation between two closely related pines with overlapping distributions, Heredity, 118, 3, (211), (2017).
    • , Gene flow between vicariant tree species: insights into savanna-forest evolutionary relationships, Tree Genetics & Genomes, 13, 2, (2017).
    • , Naturally occurring hybrids of coral reef butterflyfishes have similar fitness compared to parental species, PLOS ONE, 12, 3, (e0173212), (2017).
    • , On the origin and phylogenetic position of Arctic charr (Salvelinus alpinus complex, Salmonidae) from Lake Cherechen’ (middle Kolyma River basin): controversial genetic data, Polar Biology, 40, 4, (777), (2017).
    • , Parapatric speciation in three islands: dynamics of geographical configuration of allele sharing, Royal Society Open Science, 4, 2, (160819), (2017).
    • , Against all odds: reconstructing the evolutionary history of Scrophularia (Scrophulariaceae) despite high levels of incongruence and reticulate evolution, Organisms Diversity & Evolution, 17, 2, (323), (2017).
    • , Hybridization and genetic introgression patterns between two South American catfish along their sympatric distribution range, Hydrobiologia, 788, 1, (319), (2017).
    • , Evolution of Epigenetic Mechanisms in Animals and Their Role in Speciation, Handbook of Epigenetics, 10.1016/B978-0-12-805388-1.00027-4, (409-426), (2017).
    • , Development of 10 novel SNP-RFLP markers for quick genotyping within the black-capped (Poecile atricapillus) and Carolina (P. carolinensis) chickadee hybrid zone, Conservation Genetics Resources, 9, 2, (261), (2017).
    • , Evolution as an ecosystem process: insights from genomics, Genome, (2017).
    • , Crop-wild sunflower hybridization can mediate weediness throughout growth-stress tolerance trade-offs, Agriculture, Ecosystems & Environment, 249, (12), (2017).
    • , Lessons on Evolution from the Study of Edaphic Specialization, The Botanical Review, (2017).
    • , An integrative approach to untangling species delimitation in the Cataglyphis bicolor desert ant complex in Israel, Molecular Phylogenetics and Evolution, 115, (128), (2017).
    • , Effects of temperature and salinity on juveniles of two ascidians, one native and one invasive, and their hybrids, Journal of Experimental Marine Biology and Ecology, 10.1016/j.jembe.2017.09.019, 497, (180-187), (2017).
    • , Rearrangement moves on rooted phylogenetic networks, PLOS Computational Biology, 13, 8, (e1005611), (2017).
    • , Microevolutionary differentiation of cereal tetraploid species by the formation of recombinant genomes, Russian Journal of Genetics: Applied Research, 7, 3, (327), (2017).
    • , Occasional hybridization between a native and invasive Senecio species in Australia is unlikely to contribute to invasive success, PeerJ, 5, (e3630), (2017).
    • , Evidence for continual hybridization rather than hybrid speciation between Ligularia duciformis and L. paradoxa (Asteraceae), PeerJ, 5, (e3884), (2017).
    • , Analysis of Population Genomic Data from Hybrid Zones, Annual Review of Ecology, Evolution, and Systematics, 10.1146/annurev-ecolsys-110316-022652, 48, 1, (207-229), (2017).
    • , Genomics of introgression in the Chinese horseshoe bat (Rhinolophus sinicus) revealed by transcriptome sequencing, Biological Journal of the Linnean Society, 121, 3, (698), (2017).
    • , The potential role of hybridization in diversification and speciation in an insular plant lineage: insights from synthetic interspecific hybrids, AoB PLANTS, 9, 5, (2017).
    • , The Hybrid Origin of the Indochinese Gray Langur Trachypithecus crepusculus , International Journal of Primatology, (2017).
    • , The roles of inter- and intra-sexual selection in behavioral isolation between native and invasive pupfishes, Current Zoology, (2017).
    • , Ancient hybridization fuels rapid cichlid fish adaptive radiations, Nature Communications, 8, (14363), (2017).
    • , Genetic diversity in the Andes: variation within and between the South American species of Oreobolus R. Br. (Cyperaceae), Alpine Botany, 127, 2, (155), (2017).
    • , A history of hybrids? Genomic patterns of introgression in the True Geese, BMC Evolutionary Biology, 17, 1, (2017).
    • , Comparative Genomics of Apomictic Root-Knot Nematodes: Hybridization, Ploidy, and Dynamic Genome Change, Genome Biology and Evolution, 9, 10, (2844), (2017).
    • , Biological action in Read–Write genome evolution, Interface Focus, 10.1098/rsfs.2016.0115, 7, 5, (20160115), (2017).
    • , Widespread introgression in deep-sea hydrothermal vent mussels, BMC Evolutionary Biology, 17, 1, (2017).
    • , No evidence of queen thelytoky following interspecific crosses of the honey bees Apis cerana and Apis mellifera , Insectes Sociaux, 64, 2, (241), (2017).
    • , Fine scale mapping of genomic introgressions within the Drosophila yakuba clade, PLOS Genetics, 13, 9, (e1006971), (2017).
    • , An overlooked hybrid between the two diploid Chenopodium species in Central Europe determined by microsatellite and morphological analysis, Plant Systematics and Evolution, (2017).
    • , Natural hybridization in mangroves – an overview, Botanical Journal of the Linnean Society, 185, 2, (208), (2017).
    • , Introgressive replacement of natives by invading Arion pest slugs, Scientific Reports, 7, 1, (2017).
    • , Lost in the hybridisation vortex: high-elevation Senecio hercynicus (Compositae, Senecioneae) is genetically swamped by its congener S. ovatus in the Bavarian Forest National Park (SE Germany), Evolutionary Ecology, 31, 4, (401), (2017).
    • , Using the Ornstein–Uhlenbeck process to model the evolution of interacting populations, Journal of Theoretical Biology, 429, (35), (2017).
    • , Does competitive interaction drive species recognition in a house mouse secondary contact zone?, Behavioral Ecology, 28, 1, (212), (2017).
    • , Asymmetric Hybridization in Cattails (Typha spp.) and Its Implications for the Evolutionary Maintenance of Native Typha latifolia, Journal of Heredity, 108, 5, (479), (2017).
    • , New insight into hybridization and unidirectional introgression between Ammodytes japonicus and Ammodytes heian (Trachiniformes, Ammodytidae), PLOS ONE, 12, 6, (e0178001), (2017).
    • , Genomic Displacement and Shift of the Hybrid Zone in the Japanese Fire-Bellied Newt, Journal of Heredity, (2017).
    • , Approaches to Macroevolution: 1. General Concepts and Origin of Variation, Evolutionary Biology, 10.1007/s11692-017-9420-0, 44, 4, (427-450), (2017).
    • , Resolving incongruence: Species of hybrid origin in Columnea (Gesneriaceae), Molecular Phylogenetics and Evolution, 106, (228), (2017).
    • , Adaptive introgression from distant Caribbean islands contributed to the diversification of a microendemic adaptive radiation of trophic specialist pupfishes, PLOS Genetics, 13, 8, (e1006919), (2017).
    • , Comparison of reproductive output of hybrid sea turtles and parental species, Marine Biology, 164, 1, (2017).
    • , Strategies for Breeding Cereal Crops to Attain Sustainability with Major Emphasis on Rice, Plant Omics and Crop Breeding, 10.1201/9781315365930-16, (443-459), (2017).
    • , Detecting hybridization between sister species of Terebratulina (Brachiopoda, Cancellothyridoidea) in the North Atlantic: morphology versus molecules, Scientific Reports, 7, 1, (2017).
    • , Tipping points in the dynamics of speciation, Nature Ecology & Evolution, 1, 2, (0001), (2017).
    • , Human-mediated secondary contact of two tortoise lineages results in sex-biased introgression, Scientific Reports, 7, 1, (2017).
    • , Species Delimitation and Lineage Separation History of a Species Complex of Aspens in China, Frontiers in Plant Science, 8, (2017).
    • , Allohexaploid speciation of the two closely related species Myriophyllum spicatum and M. sibiricum (Haloragaceae), Aquatic Botany, 142, (105), (2017).
    • , The mitonuclear compatibility species concept, The Auk, 10.1642/AUK-16-201.1, 134, 2, (393-409), (2017).
    • , Molecular and morphometric data suggest the presence of a neglected species in the marine gastropod family Conidae, Molecular Phylogenetics and Evolution, 109, (421), (2017).
    • , Improved Maximum Parsimony Models for Phylogenetic Networks, Systematic Biology, (2017).
    • , Evidence for environment‐dependent introgression of adaptive genes between two red oak species with different drought adaptations, American Journal of Botany, 104, 7, (1088-1098), (2017).
    • , Incomplete lineage sorting and hybridization in the evolutionary history of closely related, endemic yellow‐flowered Aechmea species of subgenus Ortgiesia (Bromeliaceae), American Journal of Botany, 104, 7, (1073-1087), (2017).
    • , Do hybrid‐origin polyploid amphibians occupy transgressive or intermediate ecological niches compared to their diploid ancestors?, Journal of Biogeography, 43, 4, (703-715), (2015).
    • , The extent and meaning of hybridization and introgression between Siberian spruce (Picea obovata) and Norway spruce (Picea abies): cryptic refugia as stepping stones to the west?, Molecular Ecology, 25, 12, (2773-2789), (2016).
    • , Genomics of hybridization and its evolutionary consequences, Molecular Ecology, 25, 11, (2325-2332), (2016).
    • , Genetic and morphological evidence of a geographically widespread hybrid zone between two crocodile species, Crocodylus acutus and Crocodylus moreletii, Molecular Ecology, 25, 14, (3484-3498), (2016).
    • , Unidirectional diploid–tetraploid introgression among British birch trees with shifting ranges shown by restriction site‐associated markers, Molecular Ecology, 25, 11, (2413-2426), (2016).
    • , Geographic structure of genetic and phenotypic variation in the hybrid zone between uercus affinis and . laurina in Mexico, Plant Species Biology, 31, 3, (219-232), (2015).
    • , Shared and nonshared genomic divergence in parallel ecotypes of ittorina saxatilis at a local scale, Molecular Ecology, 25, 1, (287-305), (2015).
    • , Convergent recruitment of new pollinators is triggered by independent hybridization events in Narcissus, New Phytologist, 210, 2, (731-742), (2016).
    • , Genomics of local adaptation with gene flow, Molecular Ecology, 25, 10, (2144-2164), (2016).
    • , Recovery from hybrid breakdown in a marine invertebrate is faster, stronger and more repeatable under environmental stress, Journal of Evolutionary Biology, 29, 9, (1793-1803), (2016).
    • , The efficacy of sex‐chromosomal markers in studies of Cercopithecus hybridization: Discovery of a captive hybrid and applications in wild populations, Zoo Biology, 35, 1, (61-64), (2016).
    • , Hybrid dynamics in a species group of swallowtail butterflies, Journal of Evolutionary Biology, 29, 10, (1932-1951), (2016).
    • , Non‐random accumulation of LINE1‐like sequences on differentiated snake W chromosomes, Journal of Zoology, 300, 1, (67-75), (2016).
    • , Hybrid female mate choice as a species isolating mechanism: environment matters, Journal of Evolutionary Biology, 29, 4, (865-869), (2016).
    • , Little or no gene flow despite F1 hybrids at two interspecific contact zones, Ecology and Evolution, 6, 8, (2390-2404), (2016).
    • , Parental and hybrid Daphnia from the D. longispina complex: long‐term dynamics in genetic structure and significance of overwintering modes, Journal of Evolutionary Biology, 29, 4, (810-823), (2016).
    • , Local human pressures influence gene flow in a hybridizing Daphnia species complex, Journal of Evolutionary Biology, 29, 4, (720-735), (2016).
    • , Ecosystem size matters: the dimensionality of intralacustrine diversification in Icelandic stickleback is predicted by lake size, Ecology and Evolution, 6, 15, (5256-5272), (2016).
    • , Environmental (in)dependence of a hybrid zone: Insights from molecular markers and ecological niche modeling in a hybrid zone of Origanum (Lamiaceae) on the island of Crete, Ecology and Evolution, 6, 24, (8727-8739), (2016).
    • , An ancient record of an avian hybrid and the potential uses of art in ecology and conservation, Ibis, 158, 2, (444-445), (2016).
    • , Genomic heterogeneity of historical gene flow between two species of newts inferred from transcriptome data, Ecology and Evolution, 6, 13, (4513-4525), (2016).
    • , Late Pleistocene climate change promoted divergence between Picea asperata and P. crassifolia on the Qinghai–Tibet Plateau through recent bottlenecks, Ecology and Evolution, 6, 13, (4435-4444), (2016).
    • , Both morph‐ and species‐dependent asymmetries affect reproductive barriers between heterostylous species, Ecology and Evolution, 6, 17, (6223-6244), (2016).
    • , Quantifying the spatiotemporal dynamics in a chorus frog (Pseudacris) hybrid zone over 30 years, Ecology and Evolution, 6, 14, (5013-5031), (2016).
    • , Male behaviour drives assortative reproduction during the initial stage of secondary contact, Journal of Evolutionary Biology, 29, 5, (1003-1015), (2016).
    • , Genomic evidence for polyphyletic origins and interlineage gene flow within complex taxa: a case study of Picea brachytyla in the Qinghai‐Tibet Plateau, Molecular Ecology, 25, 11, (2373-2386), (2016).
    • , Genomic and functional approaches reveal a case of adaptive introgression from Populus balsamifera (balsam poplar) in P. trichocarpa (black cottonwood), Molecular Ecology, 25, 11, (2427-2442), (2016).
    • , Detecting hybridization using ancient DNA, Molecular Ecology, 25, 11, (2398-2412), (2016).
    • , Divergence history of the Carpathian and smooth newts modelled in space and time, Molecular Ecology, 25, 16, (3912-3928), (2016).
    • , Ants exhibit asymmetric hybridization in a mosaic hybrid zone, Molecular Ecology, 25, 19, (4866-4874), (2016).
    • , Diploid hybrid origin of Hippophaë gyantsensis (Elaeagnaceae) in the western Qinghai–Tibet Plateau, Biological Journal of the Linnean Society, 117, 4, (658-671), (2015).
    • , When hybrids are not hybrids: a case study of a putative hybrid zone between Cattleya coccinea and C. brevipedunculata (Orchidaceae), Botanical Journal of the Linnean Society, 181, 4, (621-639), (2016).
    • , Distinguishing contemporary hybridization from past introgression with postgenomic ancestry‐informative SNPs in strongly differentiated Ciona species, Molecular Ecology, 25, 21, (5527-5542), (2016).
    • , Transcriptome asymmetry in synthetic and natural allotetraploid wheats, revealed by RNA‐sequencing, New Phytologist, 209, 3, (1264-1277), (2015).
    • , Lineages, splits and divergence challenge whether the terms anagenesis and cladogenesis are necessary, Biological Journal of the Linnean Society, 117, 2, (165-176), (2015).
    • , Genomics of speciation and introgression in Princess cichlid fishes from Lake Tanganyika, Molecular Ecology, 25, 24, (6143-6161), (2016).
    • , Cline coupling and uncoupling in a stickleback hybrid zone, Evolution, 70, 5, (1023-1038), (2016).
    • , Hybridization and introgression in two ecologically dissimilar Fundulus hybrid zones, Evolution, 70, 5, (1051-1063), (2016).
    • , The cryptic origins of evolutionary novelty: 1000‐fold faster trophic diversification rates without increased ecological opportunity or hybrid swarm, Evolution, 70, 11, (2504-2519), (2016).
    • , Introgressive hybridization and natural selection in Darwin's finches, Biological Journal of the Linnean Society, 117, 4, (812-822), (2015).
    • , Bioinvasion threatens the genetic integrity of native diversity and a natural hybrid zone: smooth‐shelled blue mussels (Mytilus spp.) in the Strait of Magellan, Biological Journal of the Linnean Society, 117, 3, (574-585), (2015).
    • , Selection against recombinant hybrids maintains reproductive isolation in hybridizing Populus species despite F1 fertility and recurrent gene flow, Molecular Ecology, 25, 11, (2482-2498), (2016).
    • , Differential introgression and reorganization of retrotransposons in hybrid zones between wild wheats, Molecular Ecology, 25, 11, (2518-2528), (2016).
    • , Hybridization and hybrid speciation under global change, New Phytologist, 211, 4, (1170-1187), (2016).
    • , Genetic characterization of flat periwinkles (Littorinidae) from the Iberian Peninsula reveals interspecific hybridization and different degrees of differentiation, Biological Journal of the Linnean Society, 118, 3, (503-519), (2016).
    • , Current plant speciation research: unravelling the processes and mechanisms behind the evolution of reproductive isolation barriers, New Phytologist, 209, 1, (29-33), (2015).
    • , Gene flow and diversification in a species complex of Alcantarea inselberg bromeliads, Botanical Journal of the Linnean Society, 181, 3, (505-520), (2016).
    • , Hybridization between two sister species of Bromeliaceae: Vriesea carinata and V. incurvata, Botanical Journal of the Linnean Society, 181, 3, (491-504), (2016).
    • , Maintenance of species integrity in the context of a recent radiation: the case of Jamesbrittenia (Scrophulariaceae: Limoselleae) in southern Africa, Botanical Journal of the Linnean Society, 182, 1, (115-139), (2016).
    • , Hybridization and endangered species protection in the molecular era, Molecular Ecology, 25, 11, (2680-2689), (2016).
    • , Hybridization following recent secondary contact results in asymmetric genotypic and phenotypic introgression between island species of Myzomela honeyeaters, Evolution, 70, 2, (257-269), (2016).
    • , Hybridization and extinction, Evolutionary Applications, 9, 7, (892-908), (2016).
    • , What, if anything, are hybrids: enduring truths and challenges associated with population structure and gene flow, Evolutionary Applications, 9, 7, (909-923), (2016).
    • , Empirical demonstration of hybrid chromosomal races in house mice, Evolution, 70, 7, (1651-1658), (2016).
    • , Transcriptome shock in an interspecific F1 triploid hybrid of Oryza revealed by RNA sequencing, Journal of Integrative Plant Biology, 58, 2, (150-164), (2015).
    • , Introgressive Hybridization and the Evolution of Lake-Adapted Catostomid Fishes, PLOS ONE, 11, 3, (e0149884), (2016).
    • , Pollinator sharing and gene flow among closely related sympatric dioecious fig taxa, Proceedings of the Royal Society B: Biological Sciences, 283, 1828, (20152963), (2016).
    • , Revision of widespread red squirrels (genus: Tamiasciurus ) highlights the complexity of speciation within North American forests, Molecular Phylogenetics and Evolution, 100, (170), (2016).
    • , Revisiting the evolutionary events in Allium subgenus Cyathophora (Amaryllidaceae): Insights into the effect of the Hengduan Mountains Region (HMR) uplift and Quaternary climatic fluctuations to the environmental changes in the Qinghai-Tibet Plateau, Molecular Phylogenetics and Evolution, 94, (802), (2016).
    • , A comprehensive phylogeography of the Hyles euphorbiae complex (Lepidoptera: Sphingidae) indicates a ‘glacial refuge belt’, Scientific Reports, 6, 1, (2016).
    • , Morphological identification and COI barcodes of adult flies help determine species identities of chironomid larvae (Diptera, Chironomidae), Bulletin of Entomological Research, 106, 01, (34), (2016).
    • , Cryptic variation, molecular data, and the challenge of conserving plant diversity in oceanic archipelagos: the critical role of plant systematics, Korean Journal of Plant Taxonomy, 46, 2, (129), (2016).
    • , The Tangled Evolutionary Legacies of Range Expansion and Hybridization, Trends in Ecology & Evolution, 31, 9, (677), (2016).
    • , Reinforcement’s incidental effects on reproductive isolation between conspecifics, Current Zoology, 62, 2, (135), (2016).
    • , Climate, Demography, and Zoogeography Predict Introgression Thresholds in Salmonid Hybrid Zones in Rocky Mountain Streams, PLOS ONE, 11, 11, (e0163563), (2016).
    • , Genetic structure of Populus hybrid zone along the Irtysh River provides insight into plastid-nuclear incompatibility, Scientific Reports, 6, 1, (2016).
    • , Herbivory and fitness components in an introgressive hybrid swarm of Senecio hercynicus and S. ovatus (Compositae, Senecioneae), Flora - Morphology, Distribution, Functional Ecology of Plants, 220, (117), (2016).
    • , Characterization and phylogenetic analysis of fifteen NtabSPL genes in Nicotiana tabacum L. cv. Qinyan95, Development Genes and Evolution, 226, 1, (1), (2016).
    • , Disentangling Incomplete Lineage Sorting and Introgression to Refine Species-Tree Estimates for Lake Tanganyika Cichlid Fishes, Systematic Biology, (syw069), (2016).
    • , Female Sexual Preferences Toward Conspecific and Hybrid Male Mating Calls in Two Species of Polygynous Deer, Cervus elaphus and C. nippon, Evolutionary Biology, 43, 2, (227), (2016).
    • , Dynamics of mtDNA introgression during species range expansion: insights from an experimental longitudinal study, Scientific Reports, 6, 1, (2016).
    • , Timing the evolutionary history of tent-making bats, genus Uroderma (Phyllostomidae): A biogeographic context, Mammalian Biology - Zeitschrift für Säugetierkunde, 81, 6, (579), (2016).
    • , Past climate changes facilitated homoploid speciation in three mountain spiny fescues (Festuca, Poaceae), Scientific Reports, 6, 1, (2016).
    • , Hybrid origin of European Vipers (Vipera magnifica and Vipera orlovi) from the Caucasus determined using genomic scale DNA markers, BMC Evolutionary Biology, 16, 1, (2016).
    • , Genetic Structure and Evolutionary History of Three Alpine Sclerophyllous Oaks in East Himalaya-Hengduan Mountains and Adjacent Regions, Frontiers in Plant Science, 7, (2016).
    • , Surgeons and suture zones: Hybridization among four surgeonfish species in the Indo-Pacific with variable evolutionary outcomes, Molecular Phylogenetics and Evolution, 101, (203), (2016).
    • , Functional divergence of GhCFE5 homoeologs revealed in cotton fiber and Arabidopsis root cell development, Plant Cell Reports, 35, 4, (867), (2016).
    • , The importance of ecological and behavioural data in studies of hybridisation among marine fishes, Reviews in Fish Biology and Fisheries, 26, 2, (181), (2016).
    • , Hybridization as a facilitator of species range expansion, Proceedings of the Royal Society B: Biological Sciences, 283, 1839, (20161329), (2016).
    • , Integrative Taxonomy Recognizes Evolutionary Units Despite Widespread Mitonuclear Discordance: Evidence from a Rotifer Cryptic Species Complex, Systematic Biology, 65, 3, (508), (2016).
    • , Speciation, Chromosomal Rearrangements and, Encyclopedia of Evolutionary Biology, 10.1016/B978-0-12-800049-6.00074-3, (149-158), (2016).
    • , Evolutionary inventive problem-solving in biology and architecture: ArchiTRIZ and Material-Ontology, Intelligent Buildings International, 8, 2, (118), (2016).
    • , Speciation, Geography of, Encyclopedia of Evolutionary Biology, 10.1016/B978-0-12-800049-6.00333-4, (183-191), (2016).
    • , Evolutionary trends in the distylous genus Pulmonaria (Boraginaceae): Evidence of ancient hybridization and current interspecific gene flow, Molecular Phylogenetics and Evolution, 98, (63), (2016).
    • , Empirical evidence for large X-effects in animals with undifferentiated sex chromosomes, Scientific Reports, 6, 1, (2016).
    • , Differential introgression and the maintenance of species boundaries in an advanced generation avian hybrid zone, BMC Evolutionary Biology, 16, 1, (2016).
    • , Co-occurrence and reproductive synchrony do not ensure hybridization between an alien tunicate and its interfertile native congener, Evolutionary Ecology, 30, 1, (69), (2016).
    • , Genetic homogenization of the nuclear ITS loci across two morphologically distinct gentians in their overlapping distributions in the Qinghai-Tibet Plateau, Scientific Reports, 6, 1, (2016).
    • , How humans drive speciation as well as extinction, Proceedings of the Royal Society B: Biological Sciences, 283, 1833, (20160600), (2016).
    • , Transcriptomic resources and marker validation for diploid and polyploid Veronica (Plantaginaceae) from New Zealand and Europe, Applications in Plant Sciences, 4, 10, (2016).
    • , Is hybridization driving the evolution of climatic niche in Alyssum montanum, American Journal of Botany, 103, 7, (1348-1357), (2016).
    • , Correlation analysis of the mRNA and miRNA expression profiles in the nascent synthetic allotetraploid Raphanobrassica, Scientific Reports, 6, 1, (2016).
    • , Morphological and molecular investigations of Gagea (Liliaceae) in southeastern Kazakhstan with special reference to putative altitudinal hybrid zones, Plant Systematics and Evolution, 302, 8, (985), (2016).
    • , Why is population information crucial for taxonomy? A case study involving a hybrid swarm and related varieties, AoB Plants, 8, (plw070), (2016).
    • , Incomplete species recognition entails few costs in spider mites, despite first-male precedence, Behavioral Ecology and Sociobiology, 70, 8, (1161), (2016).
    • , Taxonomist’s Nightmare … Evolutionist’s Delight : An Integrative Approach Resolves Species Limits in Jumping Bristletails Despite Widespread Hybridization and Parthenogenesis, Systematic Biology, 65, 6, (947), (2016).
    • , Editorial Reconciling concepts, theory, and empirical patterns surrounding cascade reinforcement, Current Zoology, 62, 2, (131), (2016).
    • , Banning paraphylies and executing Linnaean taxonomy is discordant and reduces the evolutionary and semantic information content of biological nomenclature, Insectes Sociaux, 63, 2, (237), (2016).
    • , Movement of a Hybrid Zone Between Lineages of the Australian Glass Shrimp (Paratya australiensis), Journal of Heredity, 107, 5, (413), (2016).
    • , Disentangling the effects of isolation-by-distance and isolation-by-environment on genetic differentiation among Rhododendron lineages in the subgenus Tsutsusi, Tree Genetics & Genomes, 12, 3, (2016).
    • , Pollinator-Mediated Isolation May Be an Underestimated Factor in Promoting Homoploid Hybrid Speciation, Frontiers in Plant Science, 7, (2016).
    • , What is a gene for?, Biology & Philosophy, 31, 1, (103), (2016).
    • , Simulating and Summarizing Sources of Gene Tree Incongruence, Genome Biology and Evolution, 8, 5, (1299), (2016).
    • , Pacific Northwest Population of Lophocampa maculata Harris 1841: Evidence of a Possible Hybrid Origin, Journal of the Lepidopterists’ Society, 70, 4, (260), (2016).
    • , Sex beyond species: the first genetically analyzed case of intergeneric fertile hybridization in pinnipeds, Evolution & Development, 18, 2, (127-136), (2016).
    • , Acoustic signals in insects: A reproductive barrier and a taxonomic character, Entomological Review, 96, 9, (1127), (2016).
    • , Is cascade reinforcement likely when sympatric and allopatric populations exchange migrants?, Current Zoology, 62, 2, (155), (2016).
    • , “Islands of Divergence” in the Atlantic Cod Genome Represent Polymorphic Chromosomal Rearrangements, Genome Biology and Evolution, 8, 4, (1012), (2016).
    • , Transient hybridization, not homoploid hybrid speciation, between ancient and deeply divergent conifers, American Journal of Botany, 103, 2, (246-259), (2016).
    • , Correlated evolution of male and female reproductive traits drive a cascading effect of reinforcement inDrosophila yakuba, Proceedings of the Royal Society B: Biological Sciences, 283, 1835, (20160730), (2016).
    • , Hybridization in geese: a review, Frontiers in Zoology, 13, 1, (2016).
    • , Presumable incipient hybrid speciation of door snails in previously glaciated areas in the Caucasus, Molecular Phylogenetics and Evolution, 97, (120), (2016).
    • , Reinforcement as an initiator of population divergence and speciation, Current Zoology, 62, 2, (145), (2016).
    • , Experimental evidence for ovarian hypofunction in sparrow hybrids, Avian Research, 7, 1, (2016).
    • , Studying the genetic basis of speciation in high gene flow marine invertebrates, Current Zoology, 62, 6, (643), (2016).
    • , North African hybrid sparrows (Passer domesticus,P. hispaniolensis) back from oblivion - ecological segregation and asymmetric mitochondrial introgression between parental species, Ecology and Evolution, 6, 15, (5190), (2016).
    • , Genomics at the evolving species boundary, Current Opinion in Insect Science, 13, (7), (2016).
    • , The contribution of cytogenetics and flow cytometry for understanding the karyotype evolution in three Dorstenia (Linnaeus, 1753) species (Moraceae), Comparative Cytogenetics, 10, 1, (97), (2016).
    • , Coexistence in Close Relatives: Beyond Competition and Reproductive Isolation in Sister Taxa, Annual Review of Ecology, Evolution, and Systematics, 47, 1, (359), (2016).
    • , Do Branch Lengths Help to Locate a Tree in a Phylogenetic Network?, Bulletin of Mathematical Biology, 78, 9, (1773), (2016).
    • , A Natural Population Derived from Species Hybridizationin theDrosophila ananassaeSpecies Complexon Penang Island, Malaysia, Zoological Science, 33, 5, (467), (2016).
    • , Genetic Diversity and Hybridisation between Native and Introduced Salmonidae Fishes in a Swedish Alpine Lake, PLOS ONE, 11, 3, (e0152732), (2016).
    • , Species Concepts and Speciation, Encyclopedia of Evolutionary Biology, 10.1016/B978-0-12-800049-6.00061-5, (216-227), (2016).
    • , On the persistence of reproductive barriers inEucalyptus: the bridging of mechanical barriers to zygote formation byF1hybrids is counteracted by intrinsic post-zygotic incompatibilities, Annals of Botany, 118, 3, (431), (2016).
    • , Genomic architecture of phenotypic divergence between two hybridizing plant species along an elevational gradient, AoB Plants, 8, (plw022), (2016).
    • , Queen size dimorphism in social insects, Insectes Sociaux, 63, 1, (25), (2016).
    • , Interspecific hybrids of dwarf hamsters and Phasianidae birds as animal models for studying the genetic and developmental basis of hybrid incompatibility, Genes & Genetic Systems, 91, 2, (63), (2016).
    • , Hybrid Speciation, Encyclopedia of Evolutionary Biology, 10.1016/B978-0-12-800049-6.00072-X, (242-248), (2016).
    • , Historical environmental change in Africa drives divergence and admixture of Aedes aegypti mosquitoes: a precursor to successful worldwide colonization?, Molecular Ecology, 25, 17, (4337-4354), (2016).
    • , Marked hybridization and introgression in Ophrys sect. Pseudophrys in the western Iberian Peninsula, American Journal of Botany, 103, 4, (677-691), (2016).
    • , Strong but permeable barriers to gene exchange between sister species of Epidendrum, American Journal of Botany, 103, 8, (1472-1482), (2016).
    • , Estimating the temporal and spatial extent of gene flow among sympatric lizard populations (genus Sceloporus) in the southern Mexican highlands, Molecular Ecology, 24, 7, (1523-1542), (2015).
    • , Invasive species, disrupted chemical community dynamics and future adaptations: Commentary on Chabaane et al. 2015, Journal of Ecology, 103, 1, (118-120), (2015).
    • , Distributional dynamics and interspecific gene flow in Picea likiangensis and P. wilsonii triggered by climate change on the Qinghai‐Tibet Plateau, Journal of Biogeography, 42, 3, (475-484), (2014).
    • , Hybrid ‘superswarm’ leads to rapid divergence and establishment of populations during a biological invasion, Molecular Ecology, 24, 21, (5394-5411), (2015).
    • , Persistent inter‐ and intraspecific gene exchange within a parallel radiation of caterpillar hunter beetles (alosoma sp.) from the Galápagos, Molecular Ecology, 24, 12, (3107-3121), (2015).
    • , Sexual selection drives asymmetric introgression in wall lizards, Ecology Letters, 18, 12, (1366-1375), (2015).
    • , The Avian Hybrids Project: gathering the scientific literature on avian hybridization, Ibis, 157, 4, (892-894), (2015).
    • , Interspecific plastidial recombination in the diatom genus Pseudo‐nitzschia, Journal of Phycology, 51, 6, (1024-1028), (2015).
    • , The geography of divergence with gene flow facilitates multitrait adaptation and the evolution of pollinator isolation in Mimulus aurantiacus, Evolution, 69, 12, (3054-3068), (2015).
    • , Influence of niche similarity on hybridization between Myriophyllum sibiricum and M. spicatum, Journal of Evolutionary Biology, 28, 8, (1465-1475), (2015).
    • , Development of diagnostic microsatellite markers from whole‐genome sequences of Ammodramus sparrows for assessing admixture in a hybrid zone, Ecology and Evolution, 5, 11, (2267-2283), (2015).
    • , Hierarchical behaviour, habitat use and species size differences shape evolutionary outcomes of hybridization in a coral reef fish, Journal of Evolutionary Biology, 28, 1, (205-222), (2015).
    • , Hybridization and the spread of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae), in the northwestern United States, Evolutionary Applications, 8, 8, (834-846), (2015).
    • , Genetic admixture supports an ancient hybrid origin of the endangered Hawaiian duck, Journal of Evolutionary Biology, 28, 5, (1005-1015), (2015).
    • , Differential rates of phenotypic introgression are associated with male behavioral responses to multiple signals, Evolution, 69, 10, (2602-2612), (2015).
    • , Islands as model systems in ecology and evolution: prospects fifty years after MacArthur‐Wilson, Ecology Letters, 18, 2, (200-217), (2015).
    • , Hybridization in closely related Rhododendron species: half of all species‐differentiating markers experience serious transmission ratio distortion, Ecology and Evolution, 5, 15, (3003-3022), (2015).
    • , Differential effects of climate and species interactions on range limits at a hybrid zone: potential direct and indirect impacts of climate change, Ecology and Evolution, 5, 21, (5120-5137), (2015).
    • , Divergence and gene flow among Darwin's finches: A genome‐wide view of adaptive radiation driven by interspecies allele sharing, BioEssays, 37, 9, (968-974), (2015).
    • , Speciation by genome duplication: Repeated origins and genomic composition of the recently formed allopolyploid species Mimulus peregrinus, Evolution, 69, 6, (1487-1500), (2015).
    • , An introgressed wing pattern acts as a mating cue, Evolution, 69, 6, (1619-1629), (2015).
    • , Negligible nuclear introgression despite complete mitochondrial capture between two species of chipmunks, Evolution, 69, 8, (1961-1972), (2015).
    • , The genetic architecture of hybrid incompatibilities and their effect on barriers to introgression in secondary contact, Evolution, 69, 8, (1987-2004), (2015).
    • , Eco‐genomic analysis of the poleward range expansion of the wasp spider rgiope bruennichi shows rapid adaptation and genomic admixture, Global Change Biology, 21, 12, (4320-4332), (2015).
    • , Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards, Molecular Ecology, 24, 21, (5364-5378), (2015).
    • , Genetic diversity and distribution patterns of diploid and polyploid hybrid water frog populations (elophylax esculentus complex) across Europe, Molecular Ecology, 24, 17, (4371-4391), (2015).
    • , Introgression between invasive and native blue mussels (genus ytilus) in the central California hybrid zone, Molecular Ecology, 24, 18, (4723-4738), (2015).
    • , The origins of reproductive isolation in plants, New Phytologist, 207, 4, (968-984), (2015).
    • , Hybridization promotes speciation in Coenonympha butterflies, Molecular Ecology, 24, 24, (6209-6222), (2015).
    • , A rare case of a natural contact zone in Morocco between an autopolyploid and an allopolyploid of Centaurea aspera with sterile tetraploid hybrids, Plant Biology, 17, 3, (746-757), (2015).
    • , Quantitative trait locus mapping identifies candidate alleles involved in adaptive introgression and range expansion in a wild sunflower, Molecular Ecology, 24, 9, (2194-2211), (2015).
    • , A re‐evaluation of the homoploid hybrid origin of egilops tauschii, the donor of the wheat D‐subgenome, New Phytologist, 208, 1, (4-8), (2015).
    • , Diagnostic SNPs reveal widespread introgressive hybridization between introduced bighead and silver carp in the Mississippi River Basin, Molecular Ecology, 24, 15, (3931-3943), (2015).
    • , Species are hypotheses: avoid connectivity assessments based on pillars of sand, Molecular Ecology, 24, 3, (525-544), (2015).
    • , Sharing of chloroplast haplotypes among red oak species suggests interspecific gene flow between neighboring populations, Botany, 93, 10, (691), (2015).
    • , Divergent Macroparasite Infections in Parapatric Swiss Lake-Stream Pairs of Threespine Stickleback (Gasterosteus aculeatus), PLOS ONE, 10, 6, (e0130579), (2015).
    • , Reproduction biology and chloroplast inheritance in Bromeliaceae: a case study in Fosterella (Pitcairnioideae), Plant Systematics and Evolution, 301, 9, (2231), (2015).
    • , Hybrid zones: windows on climate change, Trends in Ecology & Evolution, 30, 7, (398), (2015).
    • , Variation in the Frequency and Extent of Hybridization between Leucosceptrum japonicum and L. stellipilum (Lamiaceae) in the Central Japanese Mainland, PLOS ONE, 10, 3, (e0116411), (2015).
    • , Pollen variation as a response to hybridisation in Populus L. section Aigeiros Duby, Euphytica, 206, 2, (433), (2015).
    • , Hybridization masks speciation in the evolutionary history of the Galápagos marine iguana, Proceedings of the Royal Society B: Biological Sciences, 282, 1809, (20150425), (2015).
    • , Detecting natural hybridization between two vulnerable Andean pupfishes (Orestias agassizii and O. luteus) representative of the Altiplano endemic fisheries, Conservation Genetics, 16, 3, (717), (2015).
    • , Exceptionally High Levels of Genetic Diversity in Wheat Curl Mite (Acari: Eriophyidae) Populations from Turkey, Journal of Economic Entomology, 108, 4, (2030), (2015).
    • , Hybridization of Two Major Termite Invaders as a Consequence of Human Activity, PLOS ONE, 10, 3, (e0120745), (2015).
    • , Silenced rRNA genes are activated and substitute for partially eliminated active homeologs in the recently formed allotetraploid, Tragopogon mirus (Asteraceae), Heredity, 114, 3, (356), (2015).
    • , Phylogenetics and phylogeography of a long-legged harvestman (Arachnida : Opiliones) in the Brazilian Atlantic Rain Forest reveals poor dispersal, low diversity and extensive mitochondrial introgression, Invertebrate Systematics, 29, 4, (386), (2015).
    • , Tracing reinforcement through asymmetrical partner preference in the European common vole Microtus arvalis, BMC Evolutionary Biology, 15, 1, (2015).
    • , Can divergent selection save the rare Senecio hercynicus from genetic swamping by its spreading congener S. ovatus (Compositae, Senecioneae)?, Flora - Morphology, Distribution, Functional Ecology of Plants, 210, (47), (2015).
    • , Nonrandom Patterns of Genetic Admixture Expose the Complex Historical Hybrid Origin of Unisexual Leaf Beetle Species in the GenusCalligrapha, The American Naturalist, 185, 1, (113), (2015).
    • , Exploring the Relationships between Mutation Rates, Life History, Genome Size, Environment, and Species Richness in Flowering Plants, The American Naturalist, 185, 4, (507), (2015).
    • , Within-island speciation with an exceptional case of distinct separation between two sibling lizard species divided by a narrow stream, Molecular Phylogenetics and Evolution, 90, (164), (2015).
    • , Historical and current introgression in a Mesoamerican hummingbird species complex: a biogeographic perspective, PeerJ, 4, (e1556), (2015).
    • , How Much Information is Needed to Infer Reticulate Evolutionary Histories?, Systematic Biology, 64, 1, (102), (2015).
    • , 250 years of hybridization between two biennial herb species without speciation, AoB Plants, 7, (plv081), (2015).
    • , Deciphering the taxonomical controversies of Rhizophora hybrids using AFLP, plastid and nuclear markers, Aquatic Botany, 125, (48), (2015).
    • , Rapid genomic DNA changes in allotetraploid fish hybrids, Heredity, 114, 6, (601), (2015).
    • , Autotetraploid rice methylome analysis reveals methylation variation of transposable elements and their effects on gene expression, Proceedings of the National Academy of Sciences, 112, 50, (E7022), (2015).
    • , The genetic architecture of hybridisation between two lineages of greenshell mussels, Heredity, 114, 3, (344), (2015).
    • , Sexiness, Individual Condition, and Species Identity: The Information Signaled by Ornaments and Assessed by Choosing Females, Evolutionary Biology, 42, 3, (251), (2015).
    • , Hybridization in Parasites: Consequences for Adaptive Evolution, Pathogenesis, and Public Health in a Changing World, PLOS Pathogens, 11, 9, (e1005098), (2015).
    • , Adaptive introgression in an African malaria mosquito coincident with the increased usage of insecticide-treated bed nets, Proceedings of the National Academy of Sciences, 112, 3, (815), (2015).
    • , A framework for incorporating evolutionary genomics into biodiversity conservation and management, Climate Change Responses, 2, 1, (2015).
    • , Species delimitation in plants using the Qinghai–Tibet Plateau endemicOrinus(Poaceae: Tridentinae) as an example, Annals of Botany, 116, 1, (35), (2015).
    • , Patterns of genetic diversity and differentiation in resistance gene clusters of two hybridizing European Populus species, Tree Genetics & Genomes, 11, 4, (2015).
    • , Additivity of ISSR Markers in Natural Hybrids of Related Forest Species Bromus benekenii and B. ramosus (Poaceae), Acta Biologica Cracoviensia s. Botanica, 57, 1, (2015).
    • , Courtship song analysis in two hybrid zones between sibling species of the Chorthippus albomarginatus group (Orthoptera, Gomphocerinae), Entomological Review, 95, 2, (166), (2015).
    • , Detecting reticulate relationships among diploid Leucanthemum Mill. (Compositae, Anthemideae) taxa using multilocus species tree reconstruction methods and AFLP fingerprinting, Molecular Phylogenetics and Evolution, 92, (308), (2015).
    • , Relationship of phenotypic variation and genetic admixture in the Saltmarsh–Nelson's sparrow hybrid zone, The Auk, 132, 3, (704), (2015).
    • , Genome reorganization in F1 hybrids uncovers the role of retrotransposons in reproductive isolation, Proceedings of the Royal Society B: Biological Sciences, 282, 1804, (20142874), (2015).
    • , Through thick and thin: Cryptic sympatric speciation in the submersed genus Najas (Hydrocharitaceae), Molecular Phylogenetics and Evolution, 82, (15), (2015).
    • , Timeframe of speciation inferred from secondary contact zones in the European tree frog radiation (Hyla arborea group), BMC Evolutionary Biology, 15, 1, (2015).
    • , Genetic divergence and phylogeographic history of two closely related species (Leucomeris decora and Nouelia insignis) across the 'Tanaka Line' in Southwest China, BMC Evolutionary Biology, 10.1186/s12862-015-0374-5, 15, 1, (2015).
    • , Genetic and morphological evidence for introgression between three species of willows, BMC Evolutionary Biology, 15, 1, (2015).
    • , Hybrid Breakdown in Cichlid Fish, PLOS ONE, 10, 5, (e0127207), (2015).
    • , Untangling reticulate evolutionary relationships among New World and Hawaiian mints (Stachydeae, Lamiaceae), Molecular Phylogenetics and Evolution, 89, (46), (2015).
    • , Examining the genetic integrity of a rare endemic Colorado cactus (Sclerocactus glaucus) in the face of hybridization threats from a close and widespread congener (Sclerocactus parviflorus), Conservation Genetics, 16, 2, (443), (2015).
    • , Mosaic genetic differentiation along environmental and geographic gradients indicate divergent selection in a white pine species complex, Evolutionary Ecology, 29, 5, (733), (2015).
    • , Adaptive Potential of Hybridization among Malaria Vectors: Introgression at the Immune Locus TEP1 between Anopheles coluzzii and A. gambiae in ‘Far-West’ Africa, PLOS ONE, 10, 6, (e0127804), (2015).
    • , Rapid acceleration of plant speciation during the Anthropocene, Trends in Ecology & Evolution, 30, 8, (448), (2015).
    • , Testing reticulate versus coalescent origins of Erica lusitanica using a species phylogeny of the northern heathers (Ericeae, Ericaceae), Molecular Phylogenetics and Evolution, 88, (121), (2015).
    • , Dynamics of Rex3 in the genomes of endangered Iberian Leuciscinae (Teleostei, Cyprinidae) and their natural hybrids, Molecular Cytogenetics, 8, 1, (2015).
    • , New possibilities arise for studies of hybridization: SNP-based markers for the multi-species Daphnia longispina complex derived from transcriptome data, Journal of Plankton Research, 37, 3, (626), (2015).
    • , S. cerevisiae × S. eubayanus interspecific hybrid, the best of both worlds and beyond, FEMS Yeast Research, 10.1093/femsyr/fov005, 15, 3, (2015).
    • , Evolutionary insights from de novo transcriptome assembly and SNP discovery in California white oaks, BMC Genomics, 16, 1, (2015).
    • , Pre-zygotic isolation in the macroalgal genus Fucus from four contact zones spanning 100-10 000 years: a tale of reinforcement?, Royal Society Open Science, 2, 2, (140538), (2015).
    • , Speciation Progress: A Case Study on the Bushcricket Poecilimon veluchianus, PLOS ONE, 10, 10, (e0139494), (2015).
    • , Postzygotic barriers isolate sympatric species of Cyrtandra (Gesneriaceae) in Hawaiian montane forest understories, American Journal of Botany, 102, 11, (1870-1882), (2015).
    • , Evaluating the Use of ABBA–BABA Statistics to Locate Introgressed Loci, Molecular Biology and Evolution, 32, 1, (244), (2015).
    • , Homoploid hybrid speciation and genome evolution via chromosome sorting, Proceedings of the Royal Society B: Biological Sciences, 282, 1807, (20150157), (2015).
    • , Introgressive hybridization facilitates adaptive divergence in a recent radiation of monkeyflowers, Proceedings of the Royal Society B: Biological Sciences, 282, 1814, (20151666), (2015).
    • , Repeated Reticulate Evolution in North American Papilio machaon Group Swallowtail Butterflies, PLOS ONE, 10, 10, (e0141882), (2015).
    • , An Integrated Framework for Hybrid Zone Models, Evolutionary Biology, 42, 3, (359), (2015).
    • , The evolution of diagnostic characters of wing venation in representatives of the subfamily Myrmeciinae (Hymenoptera, Formicidae), Entomological Review, 95, 8, (1000), (2015).
    • , Natural Hybridization between Genera That Diverged from Each Other Approximately 60 Million Years Ago, The American Naturalist, 185, 3, (433), (2015).
    • , Patterns of Reproductive Isolation inEucalyptus—A Phylogenetic Perspective, Molecular Biology and Evolution, 32, 7, (1833), (2015).
    • , Playbacks revisited: asymmetry in behavioural response across an acoustic boundary between two parapatric bird species, Behaviour, 152, 14, (1933), (2015).
    • , De novoisolation of 17 microsatellite loci for flat periwinkles (Littorina fabalisandL. obtusata) and their application for species discrimination and hybridization studies, Journal of Molluscan Studies, 81, 3, (421), (2015).
    • , Genetic differentiation and hybrid identification using microsatellite markers in closely related wild species, AoB Plants, 7, (plv084), (2015).
    • , Wide prevalence of hybridization in two sympatric grasshopper species may be shaped by their relative abundances, BMC Evolutionary Biology, 15, 1, (2015).
    • , First evidence of hybridization between golden jackal (Canis aureus) and domestic dog (Canis familiaris) as revealed by genetic markers, Royal Society Open Science, 2, 12, (150450), (2015).
    • , Field assessment of hybridization between Laricobius nigrinus and L. rubidus, predators of Adelgidae, Biological Control, 82, (1), (2015).
    • , Extensive unidirectional introgression between two salamander lineages of ancient divergence and its evolutionary implications, Scientific Reports, 4, 1, (2015).
    • , From Gene Trees to a Dated Allopolyploid Network: Insights from the Angiosperm Genus Viola (Violaceae), Systematic Biology, 64, 1, (84), (2015).
    • , Unreduced gametes: meiotic mishap or evolutionary mechanism?, Trends in Genetics, 31, 1, (5), (2015).
    • , Immediate Genetic and Epigenetic Changes in F1 Hybrids Parented by Species with Divergent Genomes in the Rice Genus (Oryza), PLOS ONE, 10, 7, (e0132911), (2015).
    • , Hybrid swarms: catalysts for multiple evolutionary events inSenecioin the British Isles, Plant Ecology & Diversity, 8, 4, (449), (2015).
    • , Molecular cytogenetics of tragelaphine and alcelaphine interspecies hybrids: hybridization, introgression and speciation in some African antelope, Biology Letters, 11, 11, (20150707), (2015).
    • , Genetic architecture and genomic patterns of gene flow between hybridizing species of Picea, Heredity, 115, 2, (153), (2015).
    • , Strong postzygotic isolation prevents introgression between two hybridizing Neotropical orchids, Epidendrum denticulatum and E. fulgens, Evolutionary Ecology, 29, 2, (229), (2015).
    • , Mating system variation and assortative mating of sympatric bromeliads (Pitcairnia spp.) endemic to neotropical inselbergs, American Journal of Botany, 102, 5, (758-764), (2015).
    • , Why evolutionary biologists should get seriously involved in ecological monitoring and applied biodiversity assessment programs, Evolutionary Applications, 7, 9, (968-983), (2014).
    • , Adaptation and exogenous selection in a icea glauca × icea engelmannii hybrid zone: implications for forest management under climate change, New Phytologist, 201, 2, (687-699), (2013).
    • , Wheat alleles introgress into selfing wild relatives: empirical estimates from approximate Bayesian computation in Aegilops triuncialis, Molecular Ecology, 23, 20, (5089-5101), (2014).
    • , Phenotypic and genetic evidence for ecological speciation of Aquilegia japonica and A. oxysepala, New Phytologist, 204, 4, (1028-1040), (2014).
    • , Gene flow and the maintenance of species boundaries, Molecular Ecology, 23, 7, (1668-1678), (2013).
    • , Evidence for natural hybridization between Primula beesiana and P. bulleyana, two heterostylous primroses in NW Yunnan, China, Journal of Systematics and Evolution, 52, 4, (500-507), (2014).
    • , Hybrid speciation through sorting of parental incompatibilities in Italian sparrows, Molecular Ecology, 23, 23, (5831-5842), (2014).
    • , Fitness dynamics within a poplar hybrid zone: II. Impact of exotic sex on native poplars in an urban jungle, Ecology and Evolution, 4, 10, (1876-1889), (2014).
    • , Maintaining microendemic primate species along an environmental gradient – parasites as drivers for species differentiation, Ecology and Evolution, 4, 24, (4751-4765), (2014).
    • , Gene Flow Happens, "Evolutionary Anthropology: Issues, News, and Reviews", 23, 1, (15-17), (2014).
    • , RAPID EVOLUTION OF REPRODUCTIVE ISOLATION BETWEEN INCIPIENT OUTCROSSING AND SELFING CLARKIA SPECIES, Evolution, 68, 10, (2885-2900), (2014).
    • , Genomic replacement of native Cobitis lutheri with introduced C. tetralineata through a hybrid swarm following the artificial connection of river systems, Ecology and Evolution, 4, 8, (1451-1465), (2014).
    • , HYBRIDIZATION, NATURAL SELECTION, AND EVOLUTION OF REPRODUCTIVE ISOLATION: A 25‐YEARS SURVEY OF AN ARTIFICIAL SYMPATRIC AREA BETWEEN TWO MOSQUITO SIBLING SPECIES OF THE Aedes mariae COMPLEX, Evolution, 68, 10, (3030-3038), (2014).
    • , Behavioural isolation may facilitate homoploid hybrid speciation in cichlid fish, Journal of Evolutionary Biology, 27, 2, (275-289), (2013).
    • , So what is a species anyway? A primatological perspective, "Evolutionary Anthropology: Issues, News, and Reviews", 23, 1, (21-23), (2014).
    • , Reproductive isolation among allopatric Drosophila montana populations, Evolution, 68, 11, (3095-3108), (2014).
    • , The effect of hybrid transgression on environmental tolerance in experimental yeast crosses, Journal of Evolutionary Biology, 27, 11, (2507-2519), (2014).
    • , HOW COMMON IS HOMOPLOID HYBRID SPECIATION?, Evolution, 68, 6, (1553-1560), (2014).
    • , Genome rearrangements derived from homoeologous recombination following allopolyploidy speciation in coffee, The Plant Journal, 78, 4, (674-685), (2014).
    • , When a clonal genome finds its way back to a sexual species: evidence from ongoing but rare introgression in the hybridogenetic water frog complex, Journal of Evolutionary Biology, 27, 3, (628-642), (2014).
    • , GENETIC REGULATORY NETWORK MOTIFS CONSTRAIN ADAPTATION THROUGH CURVATURE IN THE LANDSCAPE OF MUTATIONAL (CO)VARIANCE, Evolution, 68, 4, (950-964), (2013).
    • , PARALLEL EVOLUTION OF LOCAL ADAPTATION AND REPRODUCTIVE ISOLATION IN THE FACE OF GENE FLOW, Evolution, 68, 4, (935-949), (2013).
    • , Divergence of the gene aly in experimentally evolved cytoraces, the members of the nasuta‐albomicans complex of rosophila, Insect Molecular Biology, 23, 4, (435-443), (2014).
    • , Fitness dynamics within a poplar hybrid zone: I. Prezygotic and postzygotic barriers impacting a native poplar hybrid stand, Ecology and Evolution, 4, 9, (1629-1647), (2014).
    • , Adaptive divergence with gene flow in incipient speciation of iscanthus floridulus/sinensis complex (Poaceae), The Plant Journal, 80, 5, (834-847), (2014).
    • , Hybridization occurs between Drosophila simulans and D. sechellia in the Seychelles archipelago, Journal of Evolutionary Biology, 27, 6, (1057-1068), (2014).
    • , Relaxed trait covariance in interspecific cichlid hybrids predicts morphological diversity in adaptive radiations, Journal of Evolutionary Biology, 27, 1, (11-24), (2013).
    • , Reinforcement shapes clines in female mate discrimination in Drosophila subquinaria, Evolution, 68, 11, (3082-3094), (2014).
    • , Increased genetic divergence between two closely related fir species in areas of range overlap, Ecology and Evolution, 4, 7, (1019-1029), (2014).
    • , Hybridization in a warmer world, Ecology and Evolution, 4, 10, (2019-2031), (2014).
    • , The hidden history of the snowshoe hare, epus americanus: extensive mitochondrial DNA introgression inferred from multilocus genetic variation, Molecular Ecology, 23, 18, (4617-4630), (2014).
    • , Selection on hybrids of ecologically divergent ecotypes of a marine snail: the relative importance of exogenous and endogenous barriers, Biological Journal of the Linnean Society, 111, 2, (391-400), (2013).
    • , Butterfly genomics sheds light on the process of hybrid speciation, Molecular Ecology, 23, 18, (4441-4443), (2014).
    • , Evolutionary history of Purple cone spruce (icea purpurea) in the Qinghai–Tibet Plateau: homoploid hybrid origin and Pleistocene expansion, Molecular Ecology, 23, 2, (343-359), (2013).
    • , Hybridization facilitates evolutionary rescue, Evolutionary Applications, 7, 10, (1209-1217), (2014).
    • , Population structure and reticulate evolution of accharomyces eubayanus and its lager‐brewing hybrids, Molecular Ecology, 23, 8, (2031-2045), (2014).
    • , A multilocus evaluation of ermine (Mustela erminea) across the Holarctic, testing hypotheses of Pleistocene diversification in response to climate change, Journal of Biogeography, 41, 3, (464-475), (2013).
    • , Origin of Ostryopsis intermedia (Betulaceae) in the southeast Qinghai–Tibet Plateau through hybrid speciation, Journal of Systematics and Evolution, 52, 3, (250-259), (2014).
    • , Does genetic distance between parental species influence outcomes of hybridization among coral reef butterflyfishes?, Molecular Ecology, 23, 11, (2757-2770), (2014).
    • , Should I stay or should I go: biogeographic and evolutionary history of a polyploid complex (Chrysanthemum indicum complex) in response to Pleistocene climate change in China, New Phytologist, 201, 3, (1031-1044), (2013).
    • , Advances in Ecological Speciation: an integrative approach, Molecular Ecology, 23, 3, (513-521), (2014).
    • , Genome‐wide admixture and ecological niche modelling reveal the maintenance of species boundaries despite long history of interspecific gene flow, Molecular Ecology, 23, 8, (2046-2059), (2014).
    • , Large‐scale introduction of the Indo‐Pacific damselfish Abudefduf vaigiensis into Hawai'i promotes genetic swamping of the endemic congener A. abdominalis, Molecular Ecology, 23, 22, (5552-5565), (2014).
    • , Gene flow between nascent species: geographic, genotypic and phenotypic differentiation within and between Aquilegia formosa and A. pubescens, Molecular Ecology, 23, 22, (5589-5598), (2014).
    • , Are polyploids really evolutionary dead‐ends (again)? A critical reappraisal of Mayrose et al. (2011), New Phytologist, 202, 4, (1105-1117), (2014).
    • , Unexpected ancestry of Populus seedlings from a hybrid zone implies a large role for postzygotic selection in the maintenance of species, Molecular Ecology, 23, 17, (4316-4330), (2014).
    • , Theoretical models of the influence of genomic architecture on the dynamics of speciation, Molecular Ecology, 23, 16, (4074-4088), (2014).
    • , Introgression in hybrid ants is favored in females but selected against in males, Proceedings of the National Academy of Sciences, 111, 35, (12805), (2014).
    • , Hybridisation and diversification in the adaptive radiation of clownfishes, BMC Evolutionary Biology, 14, 1, (2014).
    • , High rates of hybridisation reveal fragile reproductive barriers between endangered Australian sea snakes, Biological Conservation, 171, (200), (2014).
    • , Interspecific crossing and genetic mapping reveal intrinsic genomic incompatibility between two Senecio species that form a hybrid zone on Mount Etna, Sicily, Heredity, 113, 3, (195), (2014).
    • , Altitudinal gradients, plant hybrid zones and evolutionary novelty, Philosophical Transactions of the Royal Society B: Biological Sciences, 369, 1648, (20130346), (2014).
    • , Disturbances as Hot Spots of Ecotypic Variation: A Case Study withDryas octopetala, Arctic, Antarctic, and Alpine Research, 46, 3, (542), (2014).
    • , Multiple hybridization events in Cardamine (Brassicaceae) during the last 150 years: revisiting a textbook example of neoallopolyploidy, Annals of Botany, 113, 5, (817), (2014).
    • , Inferring the degree of incipient speciation in secondary contact zones of closely related lineages of Palearctic green toads (Bufo viridis subgroup), Heredity, 113, 1, (9), (2014).
    • , Evidence for Mito-Nuclear and Sex-Linked Reproductive Barriers between the Hybrid Italian Sparrow and Its Parent Species, PLoS Genetics, 10, 1, (e1004075), (2014).
    • , Neutral Biogeography and the Evolution of Climatic Niches, The American Naturalist, 183, 5, (573), (2014).
    • , Ancient hybridizations among the ancestral genomes of bread wheat, Science, 345, 6194, (1250092), (2014).
    • , The Doubly Conditioned Frequency Spectrum Does Not Distinguish between Ancient Population Structure and Hybridization, Molecular Biology and Evolution, 31, 6, (1618), (2014).
    • , Mitochondrial DNA capture and divergence in Pinus provide new insights into the evolution of the genus, Molecular Phylogenetics and Evolution, 80, (20), (2014).
    • , Hybrid Speciation in a Marine Mammal: The Clymene Dolphin (Stenella clymene), PLoS ONE, 9, 1, (e83645), (2014).
    • , Population differentiation of zander (Sander lucioperca) across native and newly colonized ranges suggests increasing admixture in the course of an invasion, Evolutionary Applications, 7, 5, (555), (2014).
    • , Genome-Wide Disruption of Gene Expression in Allopolyploids but Not Hybrids of Rice Subspecies, Molecular Biology and Evolution, 31, 5, (1066), (2014).
    • , Migration-Selection Balance at Multiple Loci and Selection on Dominance and Recombination, PLoS ONE, 9, 2, (e88651), (2014).
    • , RNA-seq Reveals Transcriptomic Shock Involving Transposable Elements Reactivation in Hybrids of Young Lake Whitefish Species, Molecular Biology and Evolution, 31, 5, (1188), (2014).
    • , Genomics and the origin of species, Nature Reviews Genetics, 15, 3, (176), (2014).
    • , Genotyping-by-sequencing as a tool to infer phylogeny and ancestral hybridization: A case study in Carex (Cyperaceae), Molecular Phylogenetics and Evolution, 79, (359), (2014).
    • , Ecology, song similarity and phylogeny predict natural hybridization in an avian family, Evolutionary Ecology, 28, 2, (299), (2014).
    • , Speciation Reversal in European Whitefish (Coregonus lavaretus (L.)) Caused by Competitor Invasion, PLoS ONE, 9, 3, (e91208), (2014).
    • , Natural Hybridization and Introgression between Ligularia cymbulifera and L. tongolensis (Asteraceae, Senecioneae) in Four Different Locations, PLoS ONE, 9, 12, (e115167), (2014).
    • , Genetic Introgression and Species Boundary of Two Geographically Overlapping Pine Species Revealed by Molecular Markers, PLoS ONE, 9, 6, (e101106), (2014).
    • , The genomic landscape underlying phenotypic integrity in the face of gene flow in crows, Science, 344, 6190, (1410), (2014).
    • , Morphological differentiation despite gene flow in an endangered grasshopper, BMC Evolutionary Biology, 14, 1, (2014).
    • , Evolutionary history and population genetics of a cyprinid fish (Iberochondrostoma olisiponensis) endangered by introgression from a more abundant relative, Conservation Genetics, 15, 3, (665), (2014).
    • , Introgressive hybridization as a promoter of genome reshuffling in natural homoploid fish hybrids (Cyprinidae, Leuciscinae), Heredity, 112, 3, (343), (2014).
    • , Nuclear and plastid markers reveal the persistence of genetic identity: A new perspective on the evolutionary history of Petunia exserta, Molecular Phylogenetics and Evolution, 70, (504), (2014).
    • , Hybridization, Introgression, and the Nature of Species Boundaries, Journal of Heredity, 105, S1, (795), (2014).
    • , Genetics of Cryptic Speciation within an Arctic Mustard, Draba nivalis, PLoS ONE, 9, 4, (e93834), (2014).
    • , Progression of molecular and phenotypic diversification in resynthesized Brassica juncea (L) gene pool with determinate inflorescence, Euphytica, 199, 3, (325), (2014).
    • , Back to the wilds: Tapping evolutionary adaptations for resilient crops through systematic hybridization with crop wild relatives, American Journal of Botany, 101, 10, (1791-1800), (2014).
    • , The polyploidy revolution then…and now: Stebbins revisited, American Journal of Botany, 101, 7, (1057-1078), (2014).
    • , Turnover and accumulation of genetic diversity across large time-scale cycles of isolation and connection of populations, Proceedings of the Royal Society B: Biological Sciences, 281, 1794, (20141369), (2014).
    • , Morphological Findings of Deep Cutaneous Fungal Infections, The American Journal of Dermatopathology, 36, 7, (531), (2014).
    • , Genomics of homoploid hybrid speciation: diversity and transcriptional activity of long terminal repeat retrotransposons in hybrid sunflowers, Philosophical Transactions of the Royal Society B: Biological Sciences, 369, 1648, (20130345), (2014).
    • , Genome-Wide Congealing and Rapid Transitions across the Speciation Continuum during Speciation with Gene Flow, Journal of Heredity, 105, S1, (810), (2014).
    • , Contemporary and future studies in plant speciation, morphological/floral evolution and polyploidy: honouring the scientific contributions of Leslie D. Gottlieb to plant evolutionary biology, Philosophical Transactions of the Royal Society B: Biological Sciences, 369, 1648, (20130341), (2014).
    • , Plant speciation through chromosome instability and ploidy change: Cellular mechanisms, molecular factors and evolutionary relevance, Current Plant Biology, 1, (10), (2014).
    • , Unidirectional hybridization and reproductive barriers between two heterostylous primrose species in north-west Yunnan, China, Annals of Botany, 113, 5, (763), (2014).
    • , Reinforcement generates reproductive isolation between neighbouring conspecific populations of spadefoot toads, Proceedings of the Royal Society B: Biological Sciences, 281, 1789, (20140949), (2014).
    • , Reexamination of a Putative Diploid Hybrid Taxon Using Genetic Evidence: The Distinctiveness ofPhlox pilosasubsp.deamii(Polemoniaceae), International Journal of Plant Sciences, 175, 7, (781), (2014).
    • , Diversification of the Alpine Chipmunk, Tamias alpinus, an alpine endemic of the Sierra Nevada, California, BMC Evolutionary Biology, 14, 1, (34), (2014).
    • , Extensive Hybridization and Introgression between Melastoma candidum and M. sanguineum, PLoS ONE, 9, 5, (e96680), (2014).
    • , Identification of naturally occurring hybrids between two overexploited sciaenid species along the South African coast, Molecular Phylogenetics and Evolution, 76, (30), (2014).
    • , Growth of channel catfish (Ictalurus punctatus), blue catfish (I. furcatus), and their F1, F2, F3, and F1 reciprocal backcross hybrids in earthen ponds, Journal of Animal Science, 92, 10, (4297), (2014).
    • , Admixture of two phylogeographic lineages of the Eurasian beaver in Poland, Mammalian Biology - Zeitschrift für Säugetierkunde, 79, 5, (287), (2014).
    • , Speciation in Freshwater Fishes, Annual Review of Ecology, Evolution, and Systematics, 10.1146/annurev-ecolsys-120213-091818, 45, 1, (621-651), (2014).
    • , Interploidy hybridization in sympatric zones: the formation of pidendrum fulgens × . puniceoluteum hybrids (Epidendroideae, Orchidaceae), Ecology and Evolution, 3, 11, (3824-3837), (2013).
    • , Hybridization is important in evolution, but is speciation?, Journal of Evolutionary Biology, 26, 2, (256-258), (2013).
    • , Repeated and predictable patterns of ecotypic differentiation during a biological invasion: lake–stream divergence in parapatric Swiss stickleback, Journal of Evolutionary Biology, 26, 12, (2691-2709), (2013).
    • , Pulling together or pulling apart: hybridization in theory and practice, Journal of Evolutionary Biology, 26, 2, (294-298), (2013).
    • , Individual mating decisions and hybridization, Journal of Evolutionary Biology, 26, 2, (252-255), (2013).
    • , The unpredictable impact of hybridization, Journal of Evolutionary Biology, 26, 2, (274-275), (2013).
    • , Conditions when hybridization might predispose populations for adaptive radiation, Journal of Evolutionary Biology, 26, 2, (279-281), (2013).
    • , Beyond hybridization: diversity of interactions with heterospecifics, direct fitness consequences and the effects on mate preferences, Journal of Evolutionary Biology, 26, 2, (270-273), (2013).
    • , Hybridization and the build‐up of genomic divergence during speciation, Journal of Evolutionary Biology, 26, 2, (261-266), (2013).
    • , Hybridization: its varied forms and consequences, Journal of Evolutionary Biology, 26, 2, (276-278), (2013).
    • , The targets of selection during reinforcement, Journal of Evolutionary Biology, 26, 2, (286-287), (2013).
    • , Hybrid zones, barrier loci and the ‘rare allele phenomenon’, Journal of Evolutionary Biology, 26, 2, (288-290), (2013).
    • , Hybridization and the origin of species, Journal of Evolutionary Biology, 26, 2, (247-251), (2013).
    • , Does hybridization influence speciation?, Journal of Evolutionary Biology, 26, 2, (267-269), (2013).
    • , Hybridization, speciation and novelty, Journal of Evolutionary Biology, 26, 2, (291-293), (2013).
    • , Hybridization may rarely promote speciation, Journal of Evolutionary Biology, 26, 2, (282-285), (2013).
    • , GENETIC HITCHHIKING AND THE DYNAMIC BUILDUP OF GENOMIC DIVERGENCE DURING SPECIATION WITH GENE FLOW, Evolution, 67, 9, (2577-2591), (2013).
    • , Distribution, host plant affiliation, phenology, and phylogeny of walnut‐infesting hagoletis flies (Diptera: Tephritidae) in Mexico, Biological Journal of the Linnean Society, 110, 4, (765-779), (2013).
    • , Multilocus analyses indicate a mosaic distribution of hybrid populations in ground squirrels (genus Ictidomys), Ecology and Evolution, 3, 13, (4448-4460), (2013).
    • , Transposable elements and microevolutionary changes in natural populations, Molecular Ecology Resources, 13, 5, (765-775), (2013).
    • , Evidence for past and present hybridization in three Antarctic icefish species provides new perspectives on an evolutionary radiation, Molecular Ecology, 22, 20, (5148-5161), (2013).
    • , Steep clines within a highly permeable genome across a hybrid zone between two subspecies of the European rabbit, Molecular Ecology, 22, 9, (2511-2525), (2013).
    • , Widespread evidence for incipient ecological speciation: a meta‐analysis of isolation‐by‐ecology, Ecology Letters, 16, 7, (940-950), (2013).
    • , Widespread phenotypic and genetic divergence along altitudinal gradients in animals, Journal of Evolutionary Biology, 26, 12, (2527-2543), (2013).
    • , What is a genome?, Molecular Ecology, 22, 13, (3437-3443), (2013).
    • , Adaptive introgression in animals: examples and comparison to new mutation and standing variation as sources of adaptive variation, Molecular Ecology, 22, 18, (4606-4618), (2013).
    • , Recent rapid speciation and ecomorph divergence in Indo‐Australian sea snakes, Molecular Ecology, 22, 10, (2742-2759), (2013).
    • , Genetic drift or natural selection? Hybridization and asymmetric mitochondrial introgression in two Caribbean lizards (nolis pulchellus and Anolis krugi), Journal of Evolutionary Biology, 26, 7, (1458-1471), (2013).
    • , Outcomes of Extensive Hybridization and Introgression in Epidendrum (Orchidaceae): Can We Rely on Species Boundaries?, PLoS ONE, 8, 11, (e80662), (2013).
    • , Natürliche Hybridisierung bei Primaten, BIOspektrum, 19, 3, (253), (2013).
    • , Experimental hybridization and backcrossing reveal forces of reproductive isolation in Microbotryum, BMC Evolutionary Biology, 13, 1, (224), (2013).
    • , Hybridization may facilitate in situ survival of endemic species through periods of climate change, Nature Climate Change, 3, 12, (1039), (2013).
    • , Perspectives on the conservation of wild hybrids, Biological Conservation, 167, (390), (2013).
    • , Mitochondrial DNA Variation and Introgression in Siberian Taimen Hucho taimen, PLoS ONE, 8, 8, (e71147), (2013).
    • , The timetable for allopolyploidy in flowering plants, Annals of Botany, 112, 7, (1201), (2013).
    • , Crossing the Species Barrier: Genomic Hotspots of Introgression between Two Highly Divergent Ciona intestinalis Species, Molecular Biology and Evolution, 30, 7, (1574), (2013).
    • , Acoustic communication in insect disease vectors, Memórias do Instituto Oswaldo Cruz, 108, suppl 1, (26), (2013).
    • , Methodological challenges to realizing the potential of hybridization research, Journal of Evolutionary Biology, 26, 2, (259), (2013).
    • , Spatiotemporal dynamics of gene flow and hybrid fitness between the M and S forms of the malaria mosquito, Anopheles gambiae, Proceedings of the National Academy of Sciences, 10.1073/pnas.1316851110, 110, 49, (19854-19859), (2013).
    • , Evolutionary and ecological implications of sexual parasitism, Trends in Ecology & Evolution, 28, 5, (297), (2013).
    • , Genomewide Variation in an Introgression Line of Rice-Zizania Revealed by Whole-Genome re-Sequencing, PLoS ONE, 8, 9, (e74479), (2013).
    • , Do Heliconius butterfly species exchange mimicry alleles?, Biology Letters, 9, 4, (20130503), (2013).
    • , Genetic variation and relationships of seven sturgeon species and ten interspecific hybrids, Genetics Selection Evolution, 45, 1, (21), (2013).
    • , Rapid Speciation with Gene Flow Following the Formation of Mt. Etna, Genome Biology and Evolution, 5, 9, (1704), (2013).
    • , Genetic and morphological structure of a spruce hybrid (Picea sitchensis × P. glauca) zone along a climatic gradient, American Journal of Botany, 100, 8, (1651-1662), (2013).
    • , Discordance Between Spatial Distributions of Y-Chromosomal and Mitochondrial Haplotypes in African Green Monkeys (Chlorocebus spp.): A Result of Introgressive Hybridization or Cryptic Diversity?, International Journal of Primatology, 34, 5, (986), (2013).
    • , Geographic Mode of Speciation and Genomic Divergence, Annual Review of Ecology, Evolution, and Systematics, 44, 1, (73), (2013).
    • , The genomics of incompatibility factors and sex determination in hybridizing species of Cottus (Pisces), Heredity, 111, 6, (520), (2013).
    • , Local adaptation within a hybrid species, Heredity, 111, 4, (286), (2013).
    • , Rates of molecular evolution and diversification in plants: chloroplast substitution rates correlate with species-richness in the Proteaceae, BMC Evolutionary Biology, 13, 1, (65), (2013).
    • , Phylogenetic evidence for recent diversification of obligate coral-dwelling gobies compared with their host corals, Molecular Phylogenetics and Evolution, 69, 1, (123), (2013).
    • , Modes and Mechanisms of Speciation, Reviews in Cell Biology and Molecular Medicine, (60-93), (2016).
    • , Role of Chromosomal Reorganisations in the Human–Chimpanzee Speciation, eLS, (2014).
    • , The complex hybrid origins of the root knot nematodes revealed through comparative genomics, PeerJ, 10.7717/peerj.356, 2, (e356), (2014).
    • , Speciation through the looking‐glass, Biological Journal of the Linnean Society, , (2016).
    • , Widespread introgression of mountain hare genes into Fennoscandian brown hare populations, PLOS ONE, 10.1371/journal.pone.0191790, 13, 1, (e0191790), (2018).
    • , Analysis of a Plant Complex Resistance Gene Locus Underlying Immune-Related Hybrid Incompatibility and Its Occurrence in Nature, PLoS Genetics, 10.1371/journal.pgen.1004848, 10, 12, (e1004848), (2014).
    • , Genetic architecture of traits associated with reproductive barriers in Silene: Coupling, sex chromosomes and variation, Molecular Ecology, , (2018).
    • , LOSP: A putative marker of parasperm lineage in male reproductive system of the prosobranch mollusk Littorina obtusata, Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, , (2018).
    • , Comparative primate genomics: emerging patterns of genome content and dynamics, Nature Reviews Genetics, 10.1038/nrg3707, 15, 5, (347-359), (2014)., (2014).
    • , Genomewide evidence of environmentally mediated secondary contact of European green crab (Carcinus maenas) lineages in eastern North America, Evolutionary Applications, , (2018).
    • , Conflict between heterozygote advantage and hybrid incompatibility in haplodiploids (and sex chromosomes), Molecular Ecology, , (2018).
    • , Parallel evolution of site‐specific changes in divergent caribou lineages, Ecology and Evolution, , (2018).
    • , When homoplasy mimics hybridization: a case study of Cape hakes ( Merluccius capensis and M. paradoxus ) , PeerJ, 10.7717/peerj.1827, 4, (e1827), (2016).
    • , Extreme Environments Facilitate Hybrid Superiority – The Story of a Successful Daphnia galeata × longispina Hybrid Clone, PLOS ONE, 10.1371/journal.pone.0140275, 10, 10, (e0140275), (2015).
    • , Climate-Driven Reshuffling of Species and Genes: Potential Conservation Roles for Species Translocations and Recombinant Hybrid Genotypes, Insects, 10.3390/insects5010001, 5, 1, (1-61), (2013).
    • , Evidence for suppression of immunity as a driver for genomic introgressions and host range expansion in races of Albugo candida, a generalist parasite, eLife, 10.7554/eLife.04550, 4, (2015).
    • , Mixing It Up: The Role of Hybridization in Forest Management and Conservation under Climate Change, Forests, 10.3390/f8070237, 8, 7, (237), (2017).
    • , The evolution of sexual imprinting through reinforcement, Evolution, , (2018).