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Swainson's Thrush

A new study has shown that there is a genetic basis to the migratory routes flown by songbirds and have found that it is a relatively small cluster of genes that may govern this behaviour.

Scientists from the University of British Columbia (UBC) conducted the research, supported by The Natural Sciences and Engineering Research Council and Environment Canada, which was published in Current Biology.

Seasonal migration is one of the most remarkable phenomena in the natural world, with routes spanning thousands of kilometres and involving billions of animals.

Songbirds can travel up to 15,000 kilometres and undertake these journeys alone at night, returning to the same locations year after year.

Dr. Kira Delmore from the university’s department of zoology who led the study said. "”t's amazing that the routes and timing of such complex behaviour could be genetically determined and associated with a very small portion of the genome.

“What's even more amazing is that differences in this behaviour could be helping to maintain the huge diversity of songbirds we see in the natural world.”

Dr. Delmore and her colleagues used tiny light-level geolocators to track the migration ofclosely related groups of Swainson’s thruhses in British Columbia and their hybrids.

They then applied next-generation sequencing techniques to get and in-depth view of their genomes.

While the groups are evolutionary and genetically related, they take different routes on migration each year.

A coastal group migrates down the west coast of Canada, soutward to Mexico and Central America, while an inland group found near Kamloops migrates southeastward to the southeastern USA and then on to South America.

The two groups interbreed northeast of Vancouver, in the coastal mountains.

Previous work conducted by the team had shown that birds from the hybrid population take intermediary migration routes, which cross deserts and mountainous regions.

These inferior routes likely cause hybrid birds to have lower reproductive success, resulting in less gene flow between the groups and more differentiation between them.

By linking the migratory behaviour of hybrids to their genetic makeup, the team of scientists pinpointed a single cluster of roughly 60 genes on one chromosome that largely accounts for the difference in migration routes.

These genes play an important role in the birds’ circadian, nervous and cell signaling systems. They are also located in regions of the genome that have reduced movement of genes from one population of thrushes to the other .

"Smaller scale studies have associated some genes in this region with migratory behavior in organisms as diverse as butterflies, fish and other birds," said UBC zoologist Darren Irwin, senior author of the study.

"These results provide even stronger evidence that evolution of this genetic cluster can cause different migratory routes, facilitating the evolution of two species from one."

Swainson's thrushes were named after the English ornithologist William Swainson. They are medium sized, olive coloured thrushes with a beautiful voice typical for their genus Catharus.

Dr. Delmore has since moved from the UBC and is now with the Max Planck Institute for Evolutionary Biology, where she will continue to winnow down the set of genes responsible for migration, and use the same cutting edge techniques to investigate other populations of birds.

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