Mechanisms of population differentiation and speciation in birds

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Speciation is commonly defined as the evolution of reproductive isolation between populations. Understanding mechanisms of speciation is important both for understanding evolution and for successful conservation. However these mechansims, especially the barriers that initiate speciation, are multi-faceted, and many questions remain unanswered. For example, can philopatry (the tendency to breed at the natal site) alone promote speciation in highly mobile organisms? Does segregation during the nonbreeding season prevent gene flow between populations of migratory animals? Can sympatric populations (conspecific organisms that coexist in time and space) form new species? My research team addresses questions such as these in seabirds. Specifically, we conduct detailed analyses of recently diverged or diverging taxa to catch speciation in action, and apply state-of-the-art methods to test explicit, a priori hypotheses designed to discriminate between alternative models of speciation. Seabirds provide useful models for evolutionary genetics because their ecology is generally well understood, and they are easy to sample in large numbers. Our work initially involved temperate and arctic species, and then expanded to include tropical and subtropical seabirds. In the previous funding cycle, we found strong evidence for sympatric speciation, and also showed that, contrary to general theory, population differentiation and speciation in seabirds can occur in the absence of geographic barriers to gene flow. In the present application, I am proposing to use seabirds to test three general questions: (1) the importance of isolation-by-time (separation of breeding seasons) in promoting population differentiation and speciation; (2) the potential for foraging segregation to promote population differentation; and (3) whether strong selection can lead to genetic differentiation and speciation in populations that lack a geographic barrier to gene flow. This program will provide training for 8 graduate and 10-15 undergraduate students, and will aid both our understanding of evolution and the conservation of biodiversity.