Population genetic structure and phylogeography of common eiders (Somateria mollissima)

Abstract

Population genetic structure of Common Eiders (Somateria mollissima) was assessed at increasing spatial scales (microgeographic [<1 km] to throughout their circumpolar distribution), using molecular markers with varying modes of inheritance and rates of evolution. Population genetic subdivision was observed at all spatial scales; however, the degree of structure differed among marker types. Relatively lower levels of spatial genetic structuring were observed at bi-parentally inherited markers, and high levels of structuring were observed at a maternally inherited locus. Differences in the degree of subdivision between marker types may be attributable to the breeding biology of eiders. Pair formation occurs on the wintering grounds; where several populations of eiders interact. Female eiders exhibit high natal and breeding philopatry; whereas, males accompany females back to breeding sites and may disperse long distances between breeding seasons. Significant structuring observed at microgeographic scales indicates that eiders may nest in kin groups. Though the underlying mechanism enabling female eiders to discriminate kin is unknown, waterfowl may achieve kin recognition indirectly through association during brood rearing. Genetic signatures of philopatry among Common Eider populations do vary among Alaskan populations. No genetic structuring at mitochondrial DNA (mtDNA) was observed among islands in the Beaufort Sea in close geographic proximity (1-49 km apart). However, high structuring was observed among island groups, suggesting females are philopatric to island groups rather than individual islands. In contrast, moderate levels of genetic partitioning for mtDNA were observed among Yukon-Kuskokwim Delta (YKD) colonies (9-63 km apart); therefore, female eiders may be philopatric to individual colonies. MtDNA haplotypes representing Aleutian and YKD populations are more genetically similar to Canadian and Scandinavian populations than northern Alaska populations, indicating that southern Alaskan populations were colonized from central Canadian refugia. Data indicate that the North Slope may have been a refugium for eiders but contributed little to the post-glacial colonization of North America and Scandinavia. Finally, philopatry and winter site fidelity observed in waterfowl have predictable effects on population genetic structure. Researchers characterizing populations using molecular techniques could under- or over-estimate the degree of population genetic differentiation if estimates are based on a single marker type.