Contrasting phylogeographical patterns for springtails reflect different evolutionary histories between the Antarctic Peninsula and continental Antarctica

We examined the genetic structure among populations and regions for the springtails Cryptopygus antarcticus antarcticus and Gomphiocephalus hodgsoni (Collembola) to identify potential historical refugia and subsequent colonization routes, and to examine population growth/expansion and relative ages of population divergence. Antarctic Peninsula for C. a. antarcticus; Antarctic continent (southern Victoria Land) for G. hodgsoni. Samples were collected from 24 and 28 locations across the Antarctic Peninsula and southern Victoria Land regions for C. a. antarcticus and G. hodgsoni, respectively. We used population genetic, demographic and nested clade analyses based on mitochondrial DNA (cytochrome c oxidase subunit I and subunit II). Both species were found to have population structures compatible with the presence of historical glacial refugia on Pleistocene (2 Ma-present) time-scales, followed by post-glacial expansion generating contemporary geographically isolated populations. However, G. hodgsoni populations were characterized by a fragmented pattern with several 'phylogroups' (likely ancestral haplotypes present in high frequency) retaining strong ancestral linkages among present-day populations. Conversely, C. a. antarcticus had an excess of rare haplotypes with a much reduced volume of ancestral lineages, possibly indicating historical founder/bottleneck events and widespread expansion. We infer that these differences reflect distinct evolutionary histories in each locality despite the resident species having similar life-history characteristics. We suggest that this has predominantly been influenced by variation in the success of colonization events as a result of intrinsic historical glaciological differences between the Antarctic Peninsula and continental Antarctic environments.