Migratory behavior and its genetic basis in willow warblers Phylloscopus trochilus

Right before northern hemisphere’s summer shifts to autumn small insect-eating
birds start lengthy journeys to tropical regions. It is well established that temporary
lack food and annual changes in weather are the ultimate reasons for this behavior.
On a proximal level however, the process is poorly understood. Yet cross
continental bird migration is a widespread phenomenon that has evolved several
times independently. Different species execute specific migration routes with
remarkable precision, over narrow species-specific time windows. Even more
remarkable is that songbirds migrate alone thus relying only on internal cues. Routes
and exact winter locations can vary substantially even between populations of one
species. Crossbreeding experiments have proved that migration direction and timing
are highly heritable. However, we are still clueless on which exact genes encode
information necessary for migration. I studied the willow warbler Phylloscopus
trochilus, a common songbird that breeds across the whole of northern Eurasia and
spends the non-breeding period exclusively in tropical Africa. The far east Siberian
subspecies P.t. yakutensis winters in south-east Africa and begin the journey by
flying NW. Northern and Eastern European willow warblers P.t. acredula are
migrating towards southern Africa and start the migration by heading SSE. Western
European and southern Scandinavian populations P.t. trochilus head towards West
Africa and initiate fall migration by flying SSW. European trochilus and acredula
are nearly identical genetically except for two inversion polymorphisms on
chromosomes 1 and 5, and presence or absence of a large repeat block (MARB-a).
Far east Siberian yakutensis are genetically almost inseparable from Scandinavian
acredula, except for a set of nearly fixed differences on a small region on
chromosome 6. I deployed small tracking devices to record migratory routes of
willow warblers from breeding sites in Sweden and eastern Russia and
supplemented the tracking results with molecular methods to search for genes
associated with the migratory behaviors.