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TESTING ALTERNATIVE HYPOTHESES FOR EVOLUTIONARY DIVERSIFICATION IN AN AFRICAN SONGBIRD: RAINFOREST REFUGIA VERSUS ECOLOGICAL GRADIENTS

Authors

  • Alexander N. G. Kirschel,

    1. Department of Biological Sciences, University of Cyprus, P.O. Box 20537, Nicosia 1678, Cyprus
    2. Edward Grey Institute, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom
    3. Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Dr. South, Los Angeles, CA 90095–1606
    4. E-mail: alexander.kirschel@zoo.ox.ac.uk
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  • Hans Slabbekoorn,

    1. Behavioural Biology, Institute of Biology, Leiden University, P.O. Box 9516, 2300 RA Leiden, The Netherlands
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  • Daniel T. Blumstein,

    1. Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Dr. South, Los Angeles, CA 90095–1606
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  • Rachel E. Cohen,

    1. Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Dr. South, Los Angeles, CA 90095–1606
    2. Department of Zoology, Michigan State University, East Lansing, MI 48824
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  • Selvino R. de Kort,

    1. Division of Biology, School of Science and the Environment, Manchester Metropolitan University, Manchester M1 5GD, United Kingdom
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  • Wolfgang Buermann,

    1. Center for Tropical Research, Institute of the Environment, University of California, La Kretz Hall, Suite 300, 619 Charles E. Young Dr. South, Los Angeles, CA 90095–1496
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  • Thomas B. Smith

    1. Department of Ecology and Evolutionary Biology, University of California, 621 Charles E. Young Dr. South, Los Angeles, CA 90095–1606
    2. Center for Tropical Research, Institute of the Environment, University of California, La Kretz Hall, Suite 300, 619 Charles E. Young Dr. South, Los Angeles, CA 90095–1496
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Abstract

Geographic isolation in rainforest refugia and local adaptation to ecological gradients may both be important drivers of evolutionary diversification. However, their relative importance and the underlying mechanisms of these processes remain poorly understood because few empirical studies address both putative processes in a single system. A key question is to what extent is divergence in signals that are important in mate and species recognition driven by isolation in rainforest refugia or by divergent selection across ecological gradients? We studied the little greenbul, Andropadus virens, an African songbird, in Cameroon and Uganda, to determine whether refugial isolation or ecological gradients better explain existing song variation. We then tested whether song variation attributable to refugial or ecological divergence was biologically meaningful using reciprocal playback experiments to territorial males. We found that much of the existing song variation can be explained by both geographic isolation and ecological gradients, but that divergence across the gradient, and not geographic isolation, affects male response levels. These data suggest that ecologically divergent traits, independent of historical isolation during glacial cycles, can promote reproductive isolation. Our study provides further support for the importance of ecology in explaining patterns of evolutionary diversification in ecologically diverse regions of the planet.

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