To what extent do genes influence the migratory routes of birds? The factors that determine the long-distance migrations of seabirds are not yet fully understood. Now, a study published in the journal Molecular Ecology reveals that, in the case of Cory’s Shearwater, an individual’s genetic ancestry is a more significant factor in their migratory decisions than their social environment in the breeding colony. Among the study’s lead authors are Raül Ramos and Jacob González-Solís, from the Seabird Ecology Lab team at the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona.

The study indicates that combining individual genomics with movement tracking could help design protection strategies, better understand birds’ migratory routes and identify the key marine areas they use throughout the year.

“Beyond the example of the shearwaters, this study shows that, in other migratory species, individuals sharing the same breeding colony can have different migratory strategies depending on their genetic origin,” the authors indicate.

Hybrids of the two species follow intermediate routes

The Mediterranean Cory’s shearwater (Calonectris diomedea) and the Atlantic Cory’s shearwater (C. borealis) are migratory birds that travel long distances across the oceans. They usually breed in separate areas, but in the Strait of Gibraltar they meet and even coexist in mixed colonies where they can eventually interbreed and produce hybrid individuals.

“The research results reveal that birds breeding in the same colony may follow different migratory strategies depending on their genetic background, rather than on social learning within the breeding colony,” says Raül Ramos, from the Department of Evolutionary Biology, Ecology and Environmental Sciences at the UB.

“Moreover, when the two species hybridize, the resulting individuals follow migratory patterns that lie between those of the two species. This provides solid evidence that the long-distance migrations of these species have a genetic basis,” notes the professor.

The fact that hybrids exhibit intermediate migratory strategies shows that hybridization can generate individuals with movement patterns different from those of the parental species. “Therefore, it is necessary to take into account contact zones and introgression processes — the transfer of genes from one species to another — when interpreting connectivity between populations, and when developing conservation strategies that preserve these evolutionary processes,” explains Professor Jacob González-Solís, head of the Seabird Ecology Lab.

The study, whose first author is Beñat Garcia-Urdangarin, a PhD student in the UB’s Biodiversity doctoral programme, also involves teams from the University of Milan (Italy), Colorado State University (United States), the Association of Naturalists of the Southeast (ANSE), the Institute of Marine Sciences (ICM-CSIC) and the Doñana Biological Station (EBD-CSIC), among others. The team used geolocators, devices reconstruct movements from light-level data, to track the annual migration of around 50 individuals from six breeding colonies. The data were combined with whole-genome sequencing to determine their genetic ancestry and identify any potential hybrids.