Rapid divergence and postglacial colonization in western North American Steller's jays (Cyanocitta stelleri)

Abstract

Post-Pleistocene avian colonization of deglaciated North America occurred from multiple refugia, including a coastal refugium in the northwest. The location of a Pacific Coastal refugium is controversial; however, multiple lines of evidence suggest that it was located near the Queen Charlotte Islands (also known as Haida Gwaii). The Queen Charlotte Islands contain a disproportionately large number of endemic plants and animals including the Steller's jay Cyanocitta stelleri carlottae. Using five highly variable microsatellite markers, we studied population structure among eight populations of Steller's jay (N = 150) from geographical areas representing three subspecies in western North America: C. s. carlottae, C. s. stelleri and C. s. annectens. Microsatellite analyses revealed genetic differentiation between each of the three subspecies, although more extensive sampling of additional C. s. annectens populations is needed to clarify the level of subspecies differentiation. High levels of population structure were found among C. s. stelleri populations with significant differences in all but two pairwise comparisons. A significant isolation by distance pattern was observed amongst populations in the Pacific Northwest and Alaska. In the C. s. carlottae population, there was evidence of reduced genetic variation, higher number of private alleles than northern C. s. stelleri populations and higher levels of divergence between Queen Charlotte Island and other populations. We were unable to reject the hypothesis that the Queen Charlotte Islands served as a refugium during the Pleistocene. Steller's jay may have colonized the Queen Charlotte Islands near the end of the last glaciation or persisted throughout the Pleistocene, and this subspecies may thus represent a glacial relic. The larger number of private alleles, despite reduced genetic variation, morphological distinctiveness and high divergence from other populations suggests that the Queen Charlotte Island colonization pre-dates that of the mainland. Furthermore, our results show rapid divergence in Steller's jay populations on the mainland following the retreat of the ice sheets.