Testing alternative mechanisms of evolutionary divergence in an African rain forest passerine bird

Authors

  • T. B. Smith,

    1. Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
    2. Center for Tropical Research, Institute of the Environment, University of California, Los Angeles, CA, USA
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  • R. Calsbeek,

    1. Center for Tropical Research, Institute of the Environment, University of California, Los Angeles, CA, USA
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  • R. K. Wayne,

    1. Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
    2. Center for Tropical Research, Institute of the Environment, University of California, Los Angeles, CA, USA
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  • K. H. Holder,

    1. Department of Biology, San Francisco State University, San Francisco, CA, USA
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  • D. Pires,

    1. Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
    2. Center for Tropical Research, Institute of the Environment, University of California, Los Angeles, CA, USA
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  • C. Bardeleben

    1. Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA
    2. Center for Tropical Research, Institute of the Environment, University of California, Los Angeles, CA, USA
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Thomas B. Smith, Center for Tropical Research, Institute of the Environment, 610 Charles E. Young Drive South, 1609 Hershey Hall, Box 951496, University of California, Los Angeles, CA 90095-1496, USA.
Tel.: (310) 206 4712; Fax: (310) 825 5446; e-mail: tbsmith@ucla.edu

Abstract

Abstract Models of speciation in African rain forests have stressed either the role of isolation or ecological gradients. Here we contrast patterns of morphological and genetic divergence in parapatric and allopatric populations of the Little Greenbul, Andropadus virens, within different and similar habitats. We sampled 263 individuals from 18 sites and four different habitat types in Upper and Lower Guinea. We show that despite relatively high rates of gene flow among populations, A. virens has undergone significant morphological divergence across the savanna–forest ecotone and mountain–forest boundaries. These data support a central component of the divergence-with-gene-flow model of speciation by suggesting that despite large amounts of gene flow, selection is sufficiently intense to cause morphological divergence. Despite evidence of isolation based on neutral genetic markers, we find little evidence of morphological divergence in fitness-related traits between hypothesized refugial areas. Although genetic evidence suggests populations in Upper and Lower Guinea have been isolated for over 2 million years, morphological divergence appears to be driven more by habitat differences than geographic isolation and suggests that selection in parapatry may be more important than geographic isolation in causing adaptive divergence in morphology.

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