Genetic variation within and among populations of an arctic/alpine sweat bee (Hymenoptera: Halictidae)

Abstract

AbstractWe present the results of electrophoretic analyses of allozymes for eight population samples of the arctic/alpine sweat bee,Lasioglossum(Evylaeus)borealeSvensson, Sakagami and Ebmer. This holarctic species is found at high latitudes and at increasingly high elevations in the mountains of western North America as far south as southern Arizona. Our samples encompass a large proportion of the species' range; three samples are from Arizona, one from Utah, two from northern Canada, one from Mount Washington (the highest point in the eastern United States), and one from Sweden. Most samples had high levels of genetic variation compared with other bees, but the one from Sweden had low heterozygosity, suggesting that this location may have been comparatively recently colonized. The three northern North American samples were genetically similar despite the large geographic distances separating the localities (average > 3000 km). In contrast, the southern United States samples were (with the exception of one pairwise estimate) genetically divergent despite the small geographic distances separating them (average < 500 km). These results are consistent with earlier divergence among the southern populations, which are currently separated by regions of low elevation and inhospitable desert, than among the more northern ones. Although the data are not conclusive, they are suggestive of northward dispersal from refugia south of the ice sheets since the last glaciation.