NSF has awarded a predoctoral fellowship to Matt Wilkins for his thesis research on sexual selection and incipient speciation in barn swallows. Matt leaves in a few days for Israel and Turkey, so try to congratulate him before he disappears. The title and abstract for the project are below, as well as two photos taken by Matt last year in Turkey.
Can divergent sexual selection reduce hybridization between sympatric subspecies?
Comparative and theoretical work from a wide variety of animal taxa suggest that sexual selection plays an important role in speciation. However, very few field studies have attempted to directly assess whether divergent sexual selection pressures may be involved in the formation of reproductive barriers. In the current study, I will characterize sexual selection pressures between two subspecies of the barn swallow (Hirundo rustica transitiva and Hirundo rustica rustica) with overlapping ranges in southern Turkey. I have already established a collaboration with a researcher from Akdeniz University and a new study population near the town of Bogazkent. Because H. r. transitiva and H. r. rustica have divergent female mating preferences in allopatry, these subspecies provide an ideal opportunity to test the role of mate choice behavior in the establishment of reproductive barriers in sympatry. I will use microsatellite markers to assign paternity and derive precise measures of reproductive success in order to estimate selection pressures for morphological and song features. The same genetic markers will also be used to determine rates of gene flow between subspecies in the contact zone. Because it is known that these subspecies have different patterns of migration, feather isotopic analysis will indicate subspecies membership for individuals with intermediate phenotypes. Collectively, these data will allow for a thorough characterization of multimodal sexual selection pressures, migratory behaviors, and gene flow between two barn swallow subspecies in a contact zone. This study will determine if divergent sexual selection pressures found between subspecies in allopatry collapse in sympatry, or whether divergent mate choice cues result in stable reproductive barriers when sister taxa come into contact. This work represents the most comprehensive examination of sexual selection pressures between sympatric taxa to date, and will contribute to our understanding of how the evolution of mating behavior affects population divergence.
