Multilocus Analyses of Speciation, Hybridization, and Population Structure in Brood Parasitic Indigobirds

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Speciation, in which one ancestral population gives rise to two descendant species with distinct characteristics, is one of the fundamental evolutionary processes generating the diversity of life on earth. The possibility of sympatric speciation (i.e., without geographic isolation) has generated considerable controversy among evolutionary theorists. This research will examine the evolutionary history of the indigobirds, a group of African songbirds that provides perhaps the clearest example of sympatric speciation in vertebrates. As brood parasites, indigobirds reproduce only by laying eggs in the nests of other species, which sets the stage for speciation because songs learned from different host species serve as the principal criterion in indigobird mate choice. Field work in Tanzania will extend the geographic sampling of indigobird populations. In addition, a large set of molecular genetic markers will be analyzed using newly developed methods based on coalescent theory. These approaches are necessary to evaluate the intriguing possibility that infrequent interbreeding retards differentiation across most of the indigobird genome, even as natural selection results in divergence of the species at a small number of genes controlling host-specific adaptations.The proposed research will improve our understanding of speciation, adaptation, and the processes shaping the genetic structure of populations, which are central questions in evolutionary biology. The work will also provide training opportunities for two graduate students and will advance the field of molecular ecology by demonstrating new methods of analysis. Finally, the work will continue to raise the profile of indigobirds, whose remarkable natural history is ideal for teaching evolutionary biology and fostering interest in science and biodiversity among the public.