Old lake vs. young taxa: a comparative phylogeographic perspective on the evolution of Caspian Sea gastropods (Neritidae: Theodoxus)

The Caspian Sea has been a highly dynamic environment throughout the Quaternary and witnessed major oscillations in lake level, which were associated with changes in salinity and habitat availability. Such environmental pressures are considered to drive strong phylogeographic structure in species by forcing populations into suitable refugia. However, little is actually known on the effect of lake level fluctuations in the Caspian Sea on its aquatic biota. We compared the phylogeographic patterns of the aquatic neritid snail genus Theodoxus across the Pontocaspian region with refugial populations in southern Iran. Three gene fragments were used to determine relationships and divergence times between sampled populations in both groups. A dated phylogeny and statistical haplotype networks were generated in conjunction with analyses of molecular variance and calculations of isolation by distance using distance-based redundancy analyses. Extended Bayesian skyline plots were constructed to as...