CAREER: Seasonal migration as an ecological barrier to gene flow between hybridizing species

About This Grant

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). This project will test the role of migration in maintaining and generating biodiversity using state-of-the-art tracking and genomic technology. Individuals from nearly every animal group migrate and billions of individuals, migrate thousands of kilometers each year. Considerable variation in migration route has been documented but what is less well understood is the underlying genetic basis for that variation and the consequences for maintaining species boundaries or even promoting diversification of new species. This research will make use of a global network of radio towers to collect data on migration routes in the Swainson’s thrush, a migratory bird with eastern- and western-migrating subspecies. Individuals of this species, like many others, migrate from breeding grounds in the northwestern North America via central America and south into Chile each year. This project will evaluate the underlying genetics of migration route and the consequences of routes intermediate between the classical eastern and western routes for survival and the maintenance of the subspecies. Many of the radio towers are hosted by schools. Thus, research themes and infrastructure from this project will also be used as inspiration for teaching resources for elementary, secondary, and undergraduate students across the Americas. Education modules focused on migration and evolution will be designed for teachers, provided in English and Spanish, and offered to students internationally across the migration routes of the thrush. These modules will integrate ‘nature of science’ pedagogy while featuring international coordination as key to the protection of migrating species. Migration’s importance for speciation was proposed nearly three decades ago but has received far less attention. Many migrants breed next to one another but use different migratory routes. These routes are largely genetically determined and often involve navigation around large geographic barriers. Accordingly, hybrids in these systems are predicted to take intermediate routes that bring them over these barriers, reducing their fitness and gene flow between species. This project will test migration’s role in speciation. Specifically, state of the art infrastructure for tracking birds and genomic resources developed to genotype hundreds of individuals at low coverage will be used to (1) compare survival rates of parental and hybrid thrushes, (2) identify genetic variants underlying migratory traits, and (3) test if selection against hybrids is acting on these variants. No direct test of migration’s role in speciation has been conducted to date, leaving critical gaps in our understanding of speciation, given that differences in migration are taxonomically widespread and could help explain the predominance of young species pairs in the temperate region. Migration could also be a compelling example of an extrinsic postzygotic isolating barrier, given that reductions in hybrid fitness derive from mismatches between their intermediate behavior and parental environments. Extrinsic isolation is thought to be important in speciation, but its extent in nature is unknown, especially in vertebrates. This work will reach fields beyond speciation as well, including the genetics of complex behavior and conservation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.