The migratory behavior includes a suite of traits that the animals need for travelling between areas of reproduction and survival. Ultimately, these traits should be coordinated so that the journey is optimal regarding three key elements; timing, direction and distance. In studies of blackcaps it has been shown that these traits have a genetic basis.
Our long term goal is to identify the genes involved in the migratory program and as a model species we focus on the willow warbler, one of the most common breeding species in Sweden. Very useful for our research, it shows a sharp migratory divide in central Scandinavia. Birds in south are on average smaller and greener and migrate towards SW for wintering in West Africa, whereas northern birds are larger and greyer and migrate towards SEE for wintering in southern Africa. This migratory divide is located in a 150 km wide zone in the provinces of Jämtland and Medelpad and is probably a result of Scandinavia being colonized from two different directions after the last ice age. At the contact zone - the migratory divide - selection is acting against mixing of birds with different migratory behaviors.
We use stable isotope analyses of feathers grown at the moulting sites in Africa to infer the wintering ground and migratory direction of individual birds. To search for the genetic basis of the migratory program we have been using standard microsatellite markers, AFLP and nuclear gene sequencing, and recently microarray analyses for gene expression and Roche 454 transcriptome sequencing.
Bensch, S.,Grahn, M., Müller, N., Gay, L. & Åkesson, S. 2009. Genetic, morphological, and feather isotope variation of migratory willow warblers show gradual divergence in a ring. Molecular Ecology 18: 3087-3096.