Inter-boundary comparison between Bass Strait and southeastern Tasmania reveals taxon-specific effects of phylogeographic determinants in marine Mollusca

Comparative analysis may help elucidate how interacting influences have shaped regional phylogeography. The coasts of southeastern Australia potentially offer an opportunity for such analysis by comparison of southeastern Tasmania and Bass Strait. The latter has been extensively studied but there are fewer phylogeographic studies in southeastern Tasmania and these have mostly shown little evidence of genetic structure. The possibility that snails of the Austrocochlea constricta s.l complex have such structure was investigated here using nuclear and mitochondrial DNA sequences. Similarly to the few known examples of geographically-structured taxa in the region, especially the gastropod genus Nerita, most differentiation in A. constricta s.l. occurs between localities east and west of the Tasman Peninsula. In contrast, Nerita and A. constricta s. l. differ in their phylogeographic structure around Bass Strait. Possible explanations of inter-regional phylogeographic differences include the interaction of breeding season and current variability, whether the geographically partitioned genetic lineages represent intra-specific or species-level divergence and the decoupling of landbridge formation and sea surface temperature at the beginning and end of glacial maxima.