Migratory behavior and its genetic basis in willow warblers Phylloscopus trochilus

Sammanfattning: Right before northern hemisphere’s summer shifts to autumn small insect-eatingbirds start lengthy journeys to tropical regions. It is well established that temporarylack food and annual changes in weather are the ultimate reasons for this behavior.On a proximal level however, the process is poorly understood. Yet crosscontinental bird migration is a widespread phenomenon that has evolved severaltimes independently. Different species execute specific migration routes withremarkable precision, over narrow species-specific time windows. Even moreremarkable is that songbirds migrate alone thus relying only on internal cues. Routesand exact winter locations can vary substantially even between populations of onespecies. Crossbreeding experiments have proved that migration direction and timingare highly heritable. However, we are still clueless on which exact genes encodeinformation necessary for migration. I studied the willow warbler Phylloscopustrochilus, a common songbird that breeds across the whole of northern Eurasia andspends the non-breeding period exclusively in tropical Africa. The far east Siberiansubspecies P.t. yakutensis winters in south-east Africa and begin the journey byflying NW. Northern and Eastern European willow warblers P.t. acredula aremigrating towards southern Africa and start the migration by heading SSE. WesternEuropean and southern Scandinavian populations P.t. trochilus head towards WestAfrica and initiate fall migration by flying SSW. European trochilus and acredulaare nearly identical genetically except for two inversion polymorphisms onchromosomes 1 and 5, and presence or absence of a large repeat block (MARB-a).Far east Siberian yakutensis are genetically almost inseparable from Scandinavianacredula, except for a set of nearly fixed differences on a small region onchromosome 6. I deployed small tracking devices to record migratory routes ofwillow warblers from breeding sites in Sweden and eastern Russia andsupplemented the tracking results with molecular methods to search for genesassociated with the migratory behaviors.