Abstract
This study investigates the impact of paleoclimate on the evolutionary history of Coxiella (Tomichiidae), a group of 15 species of aquatic snail in four putative genera that are endemic to Australian salt lakes. It used a time-calibrated phylogeny, based on mitochondrial DNA ( COI ) sequence variation from 938 individuals from 14 species, to estimate the timing of diversification events in Coxiella . The four putative genera of Coxiella were estimated to have evolved in the late Miocene to late Pliocene, followed by speciation within these genera during late Pliocene to Pleistocene and subsequent divergence within species during the Pleistocene. We also used COI data from 872 individuals to compare the phylogeographic patterns and genetic diversities amongst six species. These species showed three distinctly different phylogeographic patterns, ranging from deep phylogeographic structuring to a very shallow structure in a species that appears to have undergone a range expansion after a severe bottleneck. Overall, the recent evolutionary history of Coxiella shows important parallels with those of many other taxa from southern Australia which implies a common cause, which is usually identified as the trend of increasing aridification of the Australian climate over the last ~ 15 mya.