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1. Arthropod species inhabiting disjunct xeric grasslands in the Yukon Territory, Canada may be relicts of Pleistocene steppe assemblages widespread in Beringia during glaciation, or they may be recent remnants of northward expansion of southern grassland communities during the early-Holocene Hypsithermal. To assess the likely origin of the Yukon grassland arthropod community, grassland-associated Chloropidae (Diptera) were compared from three regions: the Canadian Prairies, the Peace River region of Alberta and the southern Yukon.2. If Yukon grassland insect communities, like those in the Peace region, result primarily from northward dispersal during the Hypsithermal, chloropid assemblages in all regions would be similar, except that species richness would decline with increasing latitude. If, however, they are primarily relicts of Pleistocene steppe communities, Yukon chloropid assemblages would be distinct from southern assemblages.3. There was a latitudinal gradient of decreasing species richness and Yukon assemblages were distinct from Prairie and Peace region assemblages, based on cluster analysis, non-metric multidimensional scaling and pairwise comparisons of Morisita similarity indices.4. Community-level analyses suggest that Yukon assemblages have been separated from those in the Prairies and Peace regions since before the Hypsithermal and likely contain a mix of relict populations inhabiting Pleistocene steppe remnants in East Beringia with recent northward post-glacial dispersal from the southern Prairies. Dispersal from eastern Russia via Beringia appears to have been negligible.

BackgroundPleistocene glaciations have had an important impact on the species distribution and community composition of the North American biota. Species survived these glacial cycles south of the ice sheets and/or in other refugia, such as Beringia. In this study, we assessed, using mitochondrial DNA from three Diptera species, whether flies currently found in Beringian grasslands (1) survived glaciation as disjunct populations in Beringia and in the southern refugium; (2) dispersed northward postglacially from the southern refugium; or (3) arose by a combination of the two. Samples were collected in grasslands in western Canada: Prairies in Alberta and Manitoba; the Peace River region (Alberta); and the southern Yukon Territory. We sequenced two gene regions (658 bp of cytochrome c oxidase subunit I, 510 bp of cytochrome b) from three species of higher Diptera: one with a continuous distribution across grassland regions, and two with disjunct populations between the regions. We used a Bayesian approach to determine population groupings without a priori assumptions and performed analysis of molecular variance (AMOVA) and exact tests of population differentiation (ETPD) to examine their validity. Molecular dating was used to establish divergence times.ResultsTwo geographically structured populations were found for all species: a southern Prairie and Peace River population, and a Yukon population. Although AMOVA did not show significant differentiation between populations, ETPD did. Divergence time between Yukon and southern populations predated the Holocene for two species; the species with an ambiguous divergence time had high haplotype diversity, which could suggest survival in a Beringian refugium.ConclusionsPopulations of Diptera in Yukon grasslands could have persisted in steppe habitats in Beringia through Pleistocene glaciations. Current populations in the region appear to be a mix of Beringian relict populations and, to a lesser extent, postglacial dispersal northward from southern prairie grasslands.

BackgroundThe rarely collected genus Neossos Malloch contains three Nearctic and one western European species. Most known specimens have been collected from bird nests. Two specimens of an undescribed species of Neossos were collected by sweeping in subarctic tundra and a mesic meadow in the Yukon Territory, Canada. This represents a significant northward extension of the known Nearctic range of the genus.New informationNeossos tombstonensis sp. n. is described from the Yukon Territory. This represents the fourth described Nearctic species of Neossos. Although the type specimens were collected by sweeping, the species is predicted to be associated with bird nests, based on habits of other members of the genus. A revised key to the Nearctic species of Neossos is provided.