Phylogeography, gene flow, and the influence of Pleistocene climate changes on great basin sky island populations of the montane stonefly Doroneuria baumanni (Plecoptera: Perlidae)

Many species distributions shifted dramatically in arid regions of western North America at the end of the last glacial period. However, genetic data supporting Pleistocene divergence scenarios in sky-island populations of the Great Basin is scarce because it can be difficult to determine the mechanism underlying genetic structuring of populations. In this study, we used mtDNA to study patterns of genetic structure in the stream-dwelling montane stonefly Doroneuria baumanni. Gene trees were inferred using maximum parsimony, maximum likelihood, and Bayesian analyses. Nested clade analysis (NCA), AMOVA, coalescent modeling, and mismatch distributions were used to determine levels of genetic structure and discriminate between alternative biogeographic hypotheses. The program MDIV was used to determine whether the timing of population divergence was coincident with Pleistocene climatic fluctuations. Populations of D. baumanni in the Great Basin showed significant genetic structure that is consistent with geography. At high nesting levels, the NCA indicated that the pattern of genetic differentiation was consistent with allopatric fragmentation, but at an intermediate nesting level it was not able to discriminate between contiguous range expansion, long distance colonization, or past fragmentation. Coalescent analyses suggest that Nm < 1 for most pairwise comparisons at intermediate nesting levels. Likewise, mismatch distributions did not detect evidence for demographic expansions. These results suggest that allopatric fragmentation played a major role in shaping the genetic structure of these stonefly populations. Finally, estimated divergence times ranged from 14,600-227,000 ybp indicating that fragmentation of these Great Basin sky-island populations occurred during Pleistocene climatic fluctuations.