Highlighting convergent evolution in morphological traits in response to climatic gradient in African tropical tree species: The case of genus Guibourtia Benn.

Abstract Adaptive evolution is a major driver of organism diversification, but the links between phenotypic traits and environmental niche remain little documented in tropical trees. Moreover, trait‐niche relationships are complex because a correlation between the traits and environmental niches displayed by a sample of species may result from (a) convergent evolution if different environmental conditions have selected different sets of traits, and/or (b) phylogenetic inertia if niche and morphological differences between species are simply function of their phylogenetic divergence, in which case the trait‐niche correlation does not imply any direct causal link. Here, we aim to assess the respective roles of phylogenetic inertia and convergent evolution in shaping the differences of botanical traits and environmental niches among congeneric African tree species that evolved in different biomes. This issue was addressed with the tree genus Guibourtia Benn. (Leguminosae and Detarioideae), which contains 13 African species occupying various forest habitat types, from rain forest to dry woodlands, with different climate and soil conditions. To this end, we combined morphological data with ecological niche modelling and used a highly resolved plastid phylogeny of the 13 African Guibourtia species. First, we demonstrated phylogenetic signals in both morphological traits (Mantel test between phylogenetic and morphological distances between species: r = .24, p = .031) and environmental niches (Mantel test between phylogenetic and niche distances between species: r = .23, p = .025). Second, we found a significant correlation between morphology and niche, at least between some of their respective dimensions (Mantel's r = .32, p = .013), even after accounting for phylogenetic inertia (Phylogenetic Independent Contrast: r = .69, p = .018). This correlation occurred between some leaflet and flower traits and solar radiation, relative humidity, precipitations, and temperature range. Our results demonstrate the convergent evolution of some morphological traits in response to climatic factors in congeneric tree species and highlight the action of selective forces, along with neutral ones, in shaping the divergence between congeneric tropical plants.


| INTRODUC TI ON
Historical and environmental factors contribute both to variation in traits across species (Freckleton & Jetz, 2008). In the basic theory of quantitative genetics, a rapid evolutionary change in traits that are selectively sensitive to labile environmental variables is expected (Labra, Pienaar, & Hansen, 2009). But these expectations met complications since it is difficult to discard relative role of environmental determinants and phylogenetic effects in plant species traits variation (Grafen, 1989;Desdevises, Legendre, Azouzi, & Morand, 2003;Diniz-Filho, de Sant'Ana, & Bini, 1998;Westoby, Leishman, & Lord, 1995;Wiens & Graham, 2005). In modern phylogenetic comparative methods, this problem is particularly complex when related species have related environmental niches (Labra et al., 2009;Losos, 2008;Price, 1997;Wiens & Graham, 2005). It is then crucial to distinguish the similarity between traits of related species and niche that can be attributable to common ancestry (phylogenetic inertia) from similarity to convergent evolutionary change.
Species traits can evolve in response to selective pressures but also neutrally (Freckleton & Jetz, 2008). Adaptive processes are suspected when particular traits are associated with particular environmental conditions. However, demonstrating causal links is difficult in macroevolution. To understand what drives the evolution of species traits and niches, phylogenetic comparative methods assess the correlation between characters among species, while accounting for their phylogenetic relationships, to decipher whether trait similarity between species reflects phylogenetic inertia ( Convergent evolution is the independent evolution of a set of similar traits in organisms from different lineages subject to similar abiotic or biotic agents of natural selection (Cody & Mooney, 1978).
It is considered as an evidence of adaptation (McLennan & Brooks, 1993;Pagel, 1994) and implies causal traits-niche relationships.
Alternatively to adaptation, phylogenetic inertia has been viewed as taxon-specific limitations that force a taxon into certain combinations of traits regardless of the niche in which that taxon occurs (Morales, 2000). An apparent trait-niche association in a set of species may thus occur if the most phylogenetically related species tend to share both similar traits and similar environmental niches due to many possible processes, including genetic drift, stabilizing selection, and constraints.
To date, the mechanisms underlying plant species diversification and the evolution of their morphological traits in tropical forests remain little known. Botanists seek traits that allow distinguishing species or higher taxa but the risk that convergent evolution affects these traits is rarely assessed. Moreover, the role of environmental variation as a potential driver of adaptive morphological evolution (Ortiz-Medrano, Scantlebury, Vázquez-Lobo, Mastretta-Yanes, & Piñero, 2016) has received little attention in African tropical tree species. Understanding these mechanisms can provide important insights into the evolution of African biomes and guide strategies for their conservation (Linder, 2014).
If natural selection by abiotic factors is a main driver of the evolution of species traits, a close relationship between species traits and the environmental conditions can be expected (Ricklefs, 1987;Schluter, 1988). However, this statement remains to be demonstrated, especially for congeneric tropical tree species, because morphologically similar tree species can occur in contrasted environments, for example from dense rain forests to dry woodlands/ savannahs, so that the relative importance of adaptive processes in shaping the morphological traits that discriminate them remains unclear.
A comparative approach to explore evolutionary patterns driven by environmental variation (Freckleton & Jetz, 2008) requires a well-resolved phylogeny of the compared species to distinguish convergent evolution from spurious trait-niche association due to phylogenetic inertia (Giarla & Esselstyn, 2015). To study the relationships between traits and environmental drivers following an ecomorphological approach (Motta & Kotrschal, 1991;Wiens & Graham, 2005), Broennimann et al. (2012) proposed multivariate techniques to quantitatively compare the environmental niches between pairs of species (e.g., indices of niche overlap, niche equivalency and niche similarity). These new niche modelling tools combined with phylogenetic information (a) help to assess how the realized niches (see Soberón, 2007) of closely related species have evolved over time (e.g., Guisan & Thuiller, 2005;Ortiz-Medrano et al., 2016), and (b) allow to explain the observed biogeographical patterns and to test ecological hypotheses (Rato et al., 2015).
The present work aimed to understand the relationships between environmental niche and morphological (dis)similarity among congeneric tropical tree species while accounting for phylogenetic 4. Our results demonstrate the convergent evolution of some morphological traits in response to climatic factors in congeneric tree species and highlight the action of selective forces, along with neutral ones, in shaping the divergence between congeneric tropical plants.

K E Y W O R D S
evolutionary ecology, Guibourtia, niche comparison, phenotypic adaptation, Phylogenetic Independent Contrast, phylogenetic signal, speciation, taxonomy inertia. More specifically, we addressed the following questions: (a) Do species morphological traits and environmental niches display phylogenetic signals?, (b) are morphological and environmental (dis) similarity between species correlated?, (c) are morphological and environmental (dis)similarity still correlated after factoring out the impact of phylogenetic inertia suggesting convergent evolution? By answering these questions, we tested whether the association between morphological traits and environmental niche within congeneric species supports one of the four scenarios detailed in Figure 1.
We addressed this issue using the genus Guibourtia Benn.
(Leguminosae and Detarioideae), which includes 13 African tree species (Tosso, Daïnou, Hardy, Sinsin, & Doucet, 2015). This genus represents a good model for our questions because (a) its species occur over a wide range of habitat types (rainforests, dry forests/ savannas), and (b) a well-resolved phylogeny of this genus is now available (Tosso et al., 2018) and shows three clades, each including species occupying contrasting environments.

| Study species
The African Guibourtia species occur in a variety of vegetation types, across the Sudano-Sahelian Region, the Guineo-congolian Region, and the Zanzibar-Inhambane regional Mosaic (Tosso et al., 2015). The 13 species can be roughly categorized into species inhabiting relatively dry and seasonal climates harboring tropical dry forests (dense dry forests and woodlands) or wooded savannahs, hereafter identified by the # symbol, and species inhabiting wet/ moist and weakly seasonal climates favouring dense wet forests  Figure S1).  Léonard (1950), Aubreville (1970), Tosso et al. (2015) and Fougère-Danezan, Herendeen, Maumont, and Bruneau (2010) ( Table 1). Concerning flowers, once removed, the parts to be measured were rehydrated F I G U R E 1 Four hypothetical scenarios (Sc1 to Sc4) regarding the association between a morphological trait (M) and a dimension of the environmental niche (E) among six closely related species of known phylogeny (P). The trait and niche values are represented by the size of each gray (M) or black (E) circle. Under Sc1, species morphological traits and environmental niches evolved quickly, showing no phylogenetic signal, and independently, showing no M-E correlation. Under Sc2, morphological trait and environmental niche evolved quickly but show strong M-E correlation due to convergent evolution (same M traits selected in similar E niches). Under Sc3, both morphological trait and environmental niche evolve slowly, leading to phylogenetic signals and resulting in a M-E correlation, but there is no remaining M-E correlation when applying a PIC (Phylogenetic Independent Contrast) analysis factoring out the correlation due to phylogenetic dependence because they evolved independently. Under Sc4, a strong M-E correlation is due both to phylogenetic inertia and convergent evolution (significant PIC analysis). We expect the M-E correlation to be stronger than the M-P and E-P correlations in scenarios 2 and 4 implying convergent evolution, and to be less strong than the M-P and E-P correlations in scenario 3 implying only phylogenetic dependence in boiling water at 90°C for 3 min. The flowers (1-3) were then dissected and observed. The floral pieces were measured with a micrometer incorporated into a binocular microscope (Nachet GLI 154), at magnification ×10-40. The microscope was also used to check for the presence of glands and hairs on the leaflets, flowers, and fruits (Table 1).

| Environmental data
Environmental data corresponding to occurrence points of the 13 Guibourtia species were used to model the species environmental niches. To this end, in addition to the geographical coordinates of the 281 specimens used for the morphological characterization, we extracted georeferenced data of reliably determined specimens from Kew herbarium (K) and Naturalis herbarium (L), giving us a total of 401-presence records after removing duplicates. Climate and soil data were extracted from the Climatic Research Unit (CRU) of the University of East Anglia (Mitchell & Jones, 2005;New, Hulme, & Jones, 1999) and "FAO Digital Soil Map of the World, version 3.6." Both climatic and soil data were interpolated at 0.5° spatial resolution. To avoid redundancy in environmental information, a principal component analysis (PCA) was used as a data reduction technique (Heikkinen et al., 2006). We chose the least correlated variables that best explain the distribution of Guibourtia species: monthly means of temperature (°C), precipitation (mm), solar radiation (w/m 2 ), relative humidity (%), temperature range (°C), Potential evapotranspiration (mm), wind speed (m/s), and soil pH.

| Phylogenetic data
In a previous study, we built a high-resolution phylogeny of the genus Guibourtia using the whole chloroplast genome ( Figure S2, Tosso et al., 2018). We reconstructed the phylogeny and performed molecular dating for the 13 African species using a Bayesian MCMC analysis

| Morphological similarity
To describe the morphological similarity between species, we proceeded in the following steps. First, a morphometric distance matrix between the 281 analyzed specimens was obtained by calculating the Gower distance (Gower, 1971) using the R package "FD" (Laliberté, Legendre, & Shipley, 2014

| Environmental niche comparison
The environmental niche of species was described using a principal coordinates analysis, as done for morphological data, to facilitate the analysis of the morphology-niche relationship. Here, we considered the environmental variables extracted from the 281 specimens for which morphological data were available. We then computed the Gower distance between specimens to perform a PCoA and kept the three first axes explaining 90.10% of the total variation in environmental variables. The mean species scores along these axes were used to describe the environmental niche of the species, and the Euclidean distance between mean species scores along the three axes provided niche distances between species.
We conducted complementary environmental niche comparison analyses using the 401-presence records to further describe the degree of niche similarity and niche overlap between species, applying the approaches developed by Broennimann et al. (2012). First, to determine the limits of the area occupied by the 401-presence records (Burgman & Fox, 2003), we applied the α-hull polygons technique using the R package Alphahull (Pateiro-López & Rodrıguez-Casal, 2010). We then obtained the background data (Warren, Glor, & Turelli, 2010) for the 13 species taken together by using a buffer zone of 2,000 km around this area (except in the ocean). The buffer extent was based on preliminary analysis following the method of VanDerWal, Shoo, Graham, and Williams (2009) to optimize the predictive power of the explaining factors. We built several models for each species from a sample, varying buffer extent. Then, the area under the ROC curve (AUC) was plotted as a function of buffer extent and we selected the buffer extent corresponding to the minimal value still producing an appreciable AUC increase. The background was used to perform a smoothing technique described in Broennimann et al. (2012), which implemented an ordination technique (PCA-ent) that divides the environmental space in cells and applied a kernel density function to determine the "smoothed" density of each species occurrence in each cell.
To determine the degree of shared environmental niche between a pair of species, we calculated an index of niche overlap. This index quantifies the proportion of niche shared by the considered couple of species and can be computed by means of the Schoener's D statis-

| Testing phylogenetic signal in morphology and environmental niche
We inferred pairwise phylogenetic distance between species [P] (patristic distance; function "cophenetic.phylo" in R package "ape"; Paradis  Ives, Midford, and Garland (2007). Second, for pairwise distances, we performed Mantel tests (Mantel, 1967) between phylogenetic distance and PCoA-based morphological or niche distances. We increased the power of the test using the square root of phylogenetic distance matrix (P 1/2 ) as suggested by Hardy and Pavoine (2012).

| Assessing the morphology-environmental niche relationship
To assess whether environmental niche divergence (PCoA-based niche distance) and environmental niche overlap (D statistic) were related to morphological divergence (PCoA-based morphological distance), we used Mantel tests. To further assess the morphologyniche relationship among Guibourtia species, we applied two-block partial least squares (2B-PLS; Rohlf & Corti, 2000) analysis to explore patterns of covariation between the mean species scores along the same number of PCoA morphological and PCoA environmental niche axes. We retained ten axes to summarize 100% of the total variation in the two datasets. The Rv coefficient (Robert & Escoufier, 1976) was used to summarize the amount of covariance in each dataset that is accounted for the other dataset. The significance of all 2B-PLS summary statistics was assessed via permutation of the rows of each dataset.

| Morphological adaptation and niche divergence accounting for phylogenetic inertia
Furthermore, to verify whether the morphology-niche relationship is not simply due to phylogenetic inertia, we performed two types of analyses. First, partial Mantel test examined whether environmental niche was still related to morphological traits after accounting for phylogenetic relationships (using a matrix of phylogenetic raw distance as covariate). Second, we employed the Phylogenetically Independent Contrasts (PIC) approach (Felsenstein, 1985) to test the correlation between species scores along each of the first two morphological PCoA axes with each of the first two niche PCoA axes.
PIC analyses were also done on each morphological trait weighting in the first two niche axes in order to identify the specific morphological traits selected by each niche axis. The null hypothesis for PIC test assumes no evolutionary link between two traits (evolution by purely random genetic drift without selection). All the analyses were performed in the R platform (R Development Core Team, 2013), using the functions "pic" (R package "ape") and "mantel.partial" (R package "vegan").

| Morphological variation among species and phylogenetic signal
The first two components of the PCoA-based morphological distance explained 32.50% and 26.40% of the total variation, respectively ( Figure 2). The results showed that species associated with wet/moist climates (G. ehie and G. arnoldiana excepted) were characterized by the combination of the following main characters: large and long leaflets exhibiting marginal venation, subcoriaceous limb, apex of leaflet acuminate, axillary inflorescence, persistent and pilose bracteoles, and no pedicels and no venation on the fruit (Table S1). By contrast, the species associated with dry and seasonal climates showed small leaflets with submarginal venation, coriaceous limb, apex of leaflet obtuse, axillary and terminal inflorescence, obsolete and glabrous bracteoles, and venation on the fruit.
We detected significant phylogenetic signal for six out of 45 morphological traits (Table S1). Overall morphological similarity was significantly correlated to phylogenetic distance (Mantel test: r = .24, p = .031). This trend was also confirmed when Blomberg's K test was performed on PCoA-based morphological axes: The first axis showed significant phylogenetic signal (K = 1.2, p = .017) while the second one not (K = 0.80, p = .130). Among the 11 quantitative morphological traits, only four displayed significant K values (number of secondary suprabasilar leaf veins, length of leaflets, petiole length, and width of sepals; Table S1).

| Pattern of environmental niche evolution
The  Table S2).
F I G U R E 3 Environmental niches of the 13 African Guibourtia species in two main environmental axes produced by the principal component analysis (PCA-ent) applied on 401 occurrences. For each species, the gray-to-black shading represents the grid cell density of the species' occurrences (black being the highest density). The dashed and solid lines delimit respectively 50% and 100% of the available environment conditions in the study area. The last panel presents the contribution of variables for loading the main PCA-ent axes and the percentage of inertia explained by axes one and two. The geographical distribution of each species is presented below each PCA-ent

| Relationships between morphology and environmental niche without accounting for phylogenetic inertia
We found statistically significant correlations between species

| Morphological similarity and environmental niche resemblance accounting for phylogenetic inertia
The partial Mantel test between PCoA-based niche distance and morphological similarity using phylogenetic distances as a third matrix of covariates was statistically significant (r = .24, p < .030; Figure 4). This result must be interpreted with caution because partial Mantel tests are liberal (Guillot & Rousset, 2013 Phylogenetically Independent Contrasts analysis of the four pairwise comparisons between the two first PCoA-based environmental niche axes and morphological axes was significant only between Axis 2-morphology and Axis 1-environmental niche and marginally significant between Axis 1-morphology and Axis 2-environmental niche ( Table 2). The morphological PCoA axis 2 gathered principally flower traits (inflorescence position, type of inflorescence, pedicel, bracts, bracts hairiness, and pilosity on the external face of the sepals of flower buds) and some leaflets and fruit traits (leaflets dimension and venation, veins on the fruit surface) while axis 1 essentially summarized fruit traits (type of fruit, thickness of the fruit, gland on fruit, stipe of the fruit), seeds (arillus on the seed) and some leaflets and flowers traits (number of leaflet veins, aspect of bracteoles, and sepals; Tables S1 and S3).
Concerning the environmental niche axes, niche PCoA axis 1 was correlated with solar radiation, relative humidity, precipitations, and temperature range. This axis exhibits rainforest-dry woodland gradient whereas axis 2 was related to wind speed and potential evapotranspiration.

| D ISCUSS I ON
In this study, we demonstrated that morphological differences between African Guibourtia species are significantly associated with niche divergence, even after factoring out the impact of phylogenetic inertia. This trend was particularly evident when floral traits and leaf dimensions were considered along a rainforest-dry woodland gradient. These findings validate a set of scenarios highlighting (a) both phylogenetic inertia and convergent evolution (scenario 4) and (b) an independent evolution of some morphological traits and F I G U R E 4 Phylogeny of African Guibourtia species with species scores along the first two PCoA axes of morphological data (Ma1 and Ma2) and environmental niche data (En1 and En2)

Niche optimum
Axis 1 (solar radiation, relative humidity, precipitations and temperature range) Axis 2 (wind speed and potential evapotranspiration)

Morphology
Axis 1 (fruit, seed, leaflet and flower traits) The bold values show significance at the 5% level. environmental niche (scenario 1). They suggest that both selection forces and neutral ones contributed to the morphological divergences and similarities among Guibourtia species.

| Relationship between morphology, phylogeny, and environmental niche: evidence of adaptive forces
The recent incorporation of phylogenetic and functional information into biogeographical analyses provides a more complete understanding of evolutionary and ecological processes (Molina-Venegas, Aparicio, Slingsby, Lavergne, & Arroyo, 2015). In this study, six morphological traits, and one morphological PCoA axis representing c. a third of the morphological variation, showed significant phylogenetic signals. This finding is consistent with works of Lee and Collins (2001), Blomberg et al. (2003) and Valverde-Barrantes, Smemo, and Blackwood (2015) who found that similarity in morphometric forms largely reflects genealogical relationships.
We also proved that some Guibourtia morphological traits were correlated with environmental features. This correlation was not only due to phylogenetic inertia, as revealed by three arguments. The overall signal between morphology and environmental niche was significant in rainforest species especially when only the reproductive traits were considered. It was also significant for woodland species when all the morphological characters were taken into account together. Among species having dehiscent fruits and arillate seeds dispersed by animals, three are found in rainforests (G. tessmannii, G. pellegriniana, and G. leonensis) and one in woodlands (G. coleosperma). Except the latter one, dry forest and woodland species have indehiscent fruits with nonarillate seeds dispersed either by wind or water. This finding was highlighted by Turner (2001) and Chazdon, Careaga, Webb, and Vargas (2003) and confirms the domination of animal dispersed plants in rainforest.
Besides, the relation between PCoA-based niche distance and morphological dissimilarities was stronger for the PCoA axes considering principally flower traits and leaflets dimension along the rainforestdry woodland gradient, which evokes selection forces acting on these phenotypic characters. Rainforest species (e.g., G. tessmannii * , G. pellegriniana * , G. leonensis * etc.) have longer and larger leaflets than woodland species (G. sousae # , G. conjugata # , G. carrissoana # etc.). As specific leaf area is among the best indicator to assess the adaptation of species to light conditions and water stress for photosynthesis (Hoffmann et al., 2005), a relationship between leave size and environmental niche is expected. Species living in rainforests invest much more in leaf area (adaptation for a competitive light environment) in comparison with species of more open woodlands, while the latter invest more in root development to improve their capture of soil water during the dry season (adaptation to water stress, Hoffmann & Franco, 2003). We also observed that floral traits could be selected. Rainforest Guibourtia species have axillary inflorescences while the woodland species have axillary and terminal inflorescences. Herrera (1996) explained this phenomenon by an adaptation to insect pollinators. This kind of adaptation deserves to be more deeply investigated in African biomes.
Even though it is known that each species has specific morphological responses depending on the environmental conditions to which it is subjected to (Gratani, Meneghini, Pesoli, & Crescente, 2003), our results are among the few in Africa that prove that part of the morphological differences between congeneric tree species result from environmental adaptation. This is in line with some studies conducted within various genera, which have found the same association (Cicero & Koo, 2012;Fontanella, Feltrin, Avila, Sites, & Morando, 2012;Fort, Jouany, & Cruz, 2015). Ribeiro, Lloyd, Dean, Brown, and Bowie (2014) also demonstrated that niches differences among species are an evolutionary force shaping diversification, but studies did not clearly demonstrate a direct correlation between morphology and environmental niche. Besides, Couvreur, Porter-Morgan, Wieringa, and Chatrou (2011) by examining whether speciation was dominated by niche changes found that adaptation to climatic differences between sisters species has not been a major driver of speciation in trees of African tropical rain forests.
However, as shown in our results, the relationship between morphology and environmental niche was not evident for all morphological traits. When some leaflets and flowers traits (number of leaflet veins, aspect of bracteoles and sepals) are considered along the rainforest-woodland gradient, no significant link was detected between morphology and environmental niche. This result underlines the possible action of genetic drift as an evolutionary force, although one cannot rule out the hypothesis that selection acted again but in response to other factors and climate (Felsenstein, 1985).

| Speciation and evolutionary hypotheses within the genus Guibourtia
Considering that geographical and ecological factors could contribute to species divergence, two main hypotheses could be proposed to further understand species evolution within the genus Guibourtia. The first hypothesis is disruptive ecological adaptation (Knouft, Losos, Glor, & Kolbe, 2006), which assumes that ecological niches tend to diverge in near relatives, reducing interspecific competition (Losos et al., 2003). The second one deals with the fragmentation of favorable habitat of related species described by Acevedo, Melo-Ferreira, Real, and Alves (2014). This hypothesis supposes that the ancestor of related species occupied a large range that became fragmented in different allopatric refuges following past climatic fluctuations. Tosso et al. (2018) (Tosso et al., 2018) ultimately lead to three clades corresponding to the subgenera Gorskia, Guibourtia, and Pseudocopaiva described by Léonard (1949). This period coincides with the second major environmental perturbation that occurred from the Early to the Mid-Miocene (23-15 Mya): Humid vegetation disappeared in the Sahara, the continent moved northward, down positioning the Equator, and the rainforest belt shifted southward (Maley, 1996). During the Late Miocene and Early Pliocene, and especially with the onset of the glacial-interglacial cycles of the Quaternary, the African rainforest probably became fragmented while drier ecosystem types (dry dense forest, woodland, and savannah) expanded (Dupont, Rommerskirchen, Mollenhauer, & Schefuß, 2013). Our results, in combination with the above-mentioned work, could help hypothesize that the common ancestor of Guibourtia species probably occupied a large range in Africa. However, the common ancestor may also have had a restricted area and speciation occurred mainly during geographical expansions.
In addition to the two main hypotheses mentioned previously, it is important to underline three important points. First, each subgenus or clade ( Figure S2)  and G. schliebenii in the subgenus Gorskia). Based on all these observations, it is difficult with the current data to favor a particular mode of speciation within African Guibourtia taxa although a certain convergent evolution in morphological traits.

| CON CLUS ION
This study is the first in Africa that clearly demonstrated that similar phenotypes evolve independently in different lineages by using new genomic data set and environmental niche modelling techniques with morphological characterization using herbaria collections. We characterized the main environmental variables that constrain the potential distribution of African Guibourtia species. We also assessed the diversity and similarity of the environmental niches of these species and demonstrated phylogenetic signals of environmental niche, at some morphological traits and significant correlation between niche divergence and morphological divergence, even after accounting for phylogenetic inertia, at least for some of their respective dimensions. These results are congruent with the scenario 4 (Figure 1, Sc.4) suggest that convergent evolution has occurred. The significant differences in environmental niches spaces also reflect the morphological distances within African Guibourtia species due both to neutral processes (e.g., drift) and selection forces at a certain level.
The demonstrated link between morphology and the environmental niche for African Guibourtia species could also serve as a basis for predicting long-term phenotypic changes at the species level in the genus.

ACK N OWLED G M ENTS
This work was financially supported by the Fonds pour la