Phylogeography of the Clicking Stream Frog Strongylopus grayii (Anura, Pyxicephalidae) reveals cryptic divergence across climatic zones in an abundant and widespread taxon

Abstract

The Clicking Stream Frog (Strongylopus grayii) occurs throughout southern and eastern South Africa across summer, aseasonal and winter rainfall areas. Because of its contiguous distribution and extended breeding season this species might be expected to show a phylogeographic pattern of isolation by distance rather than divergent geographical lineages. To investigate population structure and make inferences about physical processes that have influenced gene flow in this species, two mitochondrial genes (ND2 and 16S) were sequenced for 64 frogs from across the distribution of the species. Phylogenetic analyses (parsimony and Bayesian) revealed two well-supported clades partitioning the range of this taxon, with one clade restricted to the northeast (summer rainfall) and the other restricted to the south (winter and aseasonal rainfall). The magnitude of sequence divergence between these clades is higher than expected, and is typical of levels of sequence divergence found among closely related species of pyxicephalid frogs. Phylogeographic analyses of sequence networks and spatial analysis of molecular variance (SAMOVA) revealed additional geographical structure within each of these lineages. This study demonstrates the effectiveness of climatic transitions as barriers to gene flow and as potential agents for vicariant speciation.