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Recent phylogeographic structure in a widespread ‘weedy’ Neotropical tree species, Cordia alliodora (Boraginaceae)

Authors

  • Paul D. Rymer,

    Corresponding author
    1. Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
    2. Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, NSW 2753, Australia
      Paul D. Rymer, Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia.
      E-mail: p.rymer@uws.edu.au
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  • Christopher W. Dick,

    1. Department of Ecology and Evolutionary Biology and Herbarium, University of Michigan, Ann Arbor, MI 48109-1048, USA
    2. Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancón, Republic of Panama
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  • Giovanni G. Vendramin,

    1. Istituto di Genetica Vegetale, Consiglio Nazionale delle Ricerche, 50019 Sesto Fiorentino (Firenze), Italy
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  • Anna Buonamici,

    1. Istituto di Genetica Vegetale, Consiglio Nazionale delle Ricerche, 50019 Sesto Fiorentino (Firenze), Italy
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  • David Boshier

    1. Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK
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Paul D. Rymer, Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751, Australia.
E-mail: p.rymer@uws.edu.au

Abstract

Aim  Although hundreds of tree species have broad geographic ranges in the Neotropics, little is known about how such widespread species attained disjunct distributions around mountain, ocean and xeric barriers. Here, we examine the phylogeographic structure of a widespread and economically important tree, Cordia alliodora, to: (1) test the roles of vicariance and dispersal in establishing major range disjunctions, (2) determine which geographic regions and/or habitats contain the highest levels of genetic diversity, and (3) infer the geographic origin of the species.

Location  Twenty-five countries in Central and South America, and the West Indies.

Methods  Chloroplast simple sequence repeats (cpSSR; eight loci) were assayed in 67 populations (240 individuals) sampled from the full geographic range of C. alliodora. Chloroplast (trnH–psbA) and nuclear (internal transcribed spacer, ITS) DNA sequences were sampled from a geographically representative subset. Genetic structure was determined with samova, structure and haplotype networks. Analysis of molecular variance (AMOVA) and rarefaction analyses were used to compare regional haplotype diversity and differentiation.

Results  Although the ITS region was polymorphic it revealed limited phylogeographic structure, and trnH–psbA was monomorphic. However, structure analysis of cpSSR variation recovered three broad demes spanning Central America (Deme 1), the Greater Antilles and the Chocó (Deme 2), and the Lesser Antilles and cis-Andean South America (Deme 3). samova showed two predominant demes (Deme 1 + 2 and Deme 3). The greatest haplotype diversity was detected east of the Andes, while significantly more genetic variation was partitioned among trans-Andean populations. Populations experiencing high precipitation seasonality (dry ecotype) had greater levels of genetic variation.

Main conclusions  Cordia alliodora displayed weak cis- and trans-Andean phylogeographic structure based on DNA sequence data, indicative of historical dispersal around this barrier and genetic exchange across its broad range. The cpSSR data revealed phylogeographic structure corresponding to three biogeographic zones. Patterns of genetic diversity are indicative of an origin in the seasonally dry habitats of South America. Therefore, C. alliodora fits the disperser hypothesis for widespread Neotropical species. Dispersal is evident in the West Indies and the northern Andean cordilleras. The dry ecotype harbours genetic variation that is likely to represent the source for the establishment of populations under future warmer and drier climatic scenarios.

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