Clock genes and their role in migratory phenotype among Passer sparrows

Abstract

Across the avian lineage, closely related species, or even populations within the same species may display differing migratory phenotypes. The many components of migratory behaviour are inherited as one migratory gene package leaving most, if not all, birds with the necessary machinery to migrate. The appropriate selection pressure can thus cause a switch from migratory to sedentary behaviour over relatively few generations. My study species, the hybrid Italian sparrow and its parental species, the house sparrow and the Spanish sparrow serve as an example of this. The house sparrow and the Italian sparrow are both predominantly sedentary species, while the Spanish sparrow differs by being migratory throughout most of its native habitat. Interestingly, different patterns of migration are observed even within species. Among Spanish sparrows, certain island-living populations have ceased to migrate while a subspecies of the house sparrow living in Central Asia has retained the putatively ancestral migratory phenotype. Although migratory behaviour is known to be under genetic control, less is known regarding which genes are involved. In this study, I attempted to shed light on associations between migratory phenotype and genotype in my focal species by employing a candidate gene approach combined with data from whole genome resequencing. As migration is a seasonal behaviour it is likely to be under the influence of circadian rhythm. I therefore selected 20 candidate genes reported to have a function influencing the circadian clock. Within these genetic regions, I performed a search for fixed differences between migratory and sedentary populations as well as population genetics analyses. However, these tests did not reveal any signs of selection acting on any of the candidate genes. My results are nevertheless consistent with much of the research to date. Any attempts at uncovering the genetics of migration thus far have failed to reveal associations that can be generalized across taxa, highlighting the need for further research.