Genetic Basis For Epic Songbird Migration Uncovered

The Swainson's thrush (Catharus ustulatus) migrate thousands of kilometers. Double Brow Imagery/Shutterstock

From wildebeests to sea turtles to butterflies, animals around the world are always on the move. Often traveling thousands of kilometers during their journeys, how the creatures manage this amazing feat is still largely a mystery. A recent study on migrating songbirds in the US has found that their movements across the country may be hardwired into them, and it even identified a small cluster of genes that could be responsible.

“It's amazing that the routes and timing of such complex behavior could be genetically determined and associated with a very small portion of the genome,” explains Kira Delmore, who led the study published in Current Biology. “What's even more amazing is that differences in this behavior could be helping to maintain the huge diversity of songbirds we see in the natural world.”

From the Pacific Coast of North America, the Swainson’s thrush partakes in an epic migration each year. Only weighing in at around 30 grams, the little songbird manages to fly south from its breeding grounds along the west coast, through the states, and then to Central and South America. Yet that is not the only route the birds take. While some go south, another population of the thrushes instead head south-east, before baring fully south to end up in Central America.

Researchers attached tiny sensors to the back of the birds to track their migrations. Kira Delmore/University of British Columbia

Despite these differing routes, the two populations are still evolutionarily and genetically related, and even mate to produce hybrid thrushes. What is interesting is that these hybrids don’t follow the migration pattern of either of their parents, but instead follow a route intermediary of the two. This middle route, through which the birds cross deserts and mountains, means the hybrids have lower reproductive success and are less fit than their parents, resulting in fewer surviving. This therefore reduces the gene flow between the two normal groups of thrushes, effectively segregating the populations, something that could eventually lead to the single species becoming two.

The researchers looked into the genetics behind the two migrating groups of thrushes, and the hybrids they produce when they mate, and were able to pinpoint the section of DNA that seems to be influencing their patterns. The cluster, found on a single chromosome, contains about 60 genes and is thought to largely account for the differences in migration routes, while also being involved with the birds’ circadian, nervous, and cell signaling.

“Smaller scale studies have associated some genes in this region with migratory behavior in organisms as diverse as butterflies, fish and other birds,” says Darren Irwin, senior author of the paper. The results provide yet more evidence for a genetic basis to migration, and that this in turn can lead to the evolution of new species.

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