Do Deep Mitochondrial DNA Divergences within Intertidal Gastropods Reveal Phylogeographic Signals from Earlier Glacial Cycles?

Abstract

Climatic cycles have frequently been hypothesised to influence the phylogeography of temperate marine organisms through such factors as hydrological changes and landbridge formation at glacial maxima. However, it is rarely considered whether observed phylogeographic patterns are predominantly influenced by the most recent cycle or those that preceded it. Whether high genetic divergences within intertidal taxa provide an opportunity to investigate such questions is studied here. Three southeastern Australian gastropod taxa that exhibit such divergence were studied, namely, Ascorhis tasmanica, Phallomedusa solida and the regions’ two species of the genus Nerita. Maximum likelihood phylogenetic analyses revealed bootstrap-supported clades within Nerita atramentosa, N. melanotragus and P. solida each of which may have been influenced by climatically induced isolation in previous glacial cycles. These clades are all now very widely distributed within the ranges of their respective species. The loss of variants resulting in the divergence of the haplotypes in the clades may be stochastic but was more likely due to selection, at least for P. solida. Ascorhis tasmanica was revealed to have a comparatively large number of sporadically distributed divergent groups; however, their evolution may have been more influenced by factors other than climate cycles.