Isolating barriers and microevolution in sympatric populations of the blackcap (Sylvia atricapilla)

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Speciation is the core topic of evolutionary biology, but the mechanisms leading to reproductive isolation between populations are often unknown as they have to be identified in retrospective. Incipient ongoing isolation in sympatric populations thus offers a unique window to evaluate the relative importance of different isolating barriers. The blackcap [Sylvia atricapilla) is an ideal model system because it developed a migratory shiff with a known genetic basis in the last 60 years. We found that sympatric populations with distinct migratory routes differ genetically. We will study genetic and phenotypic characters of these populations to analyse local adaptation and infer the mode of selection. We account for genetic driff using neutral genetic markers and assess genetic adaptation analysing an avian clock gene. We combine genetic with behavioural analyses of spring arrival and courtship to assess alternative hypotheses on the evolution of reproductive isolation. This approach allows to evaluate whether incipient reproductive isolation is a by-product of non-selective assortative mating or whether it is adaptive driven by premating behavioural isolation or postmating isolation owing to hybrid inviability. We can thus quantify the evolutionary significance of the shift in migratory behaviour that occurred 60 years ago.