, Volume 43, Issue 2, pp 73-85

Possible drivers of biodiversity generation in the Siphonaria of southeastern Australia

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Abstract

An inter-species approach may reveal insights into biodiversity that are not available by studying single-species phylogeography. Here, we have used this approach to investigate biodiversity generation in Siphonaria, a prominent component of the intertidal fauna of a biogeographically complex region of southeastern Australia. We collected DNA sequences of cytochrome c oxidase (COI) and internal transcribed spacer 2 (ITS-2) from the five species of Siphonaria in the region to study factors such as contemporary hydrology and historical geographic barriers that are known to be important in intra-species phylogeography. Except for the closely-related Siphonaria funiculata and S. tasmanica, the genetic divergences between studied species were deep and could not be related directly to intra-regional factors. In particular, isolation induced by the Bassian Isthmus landbridge at glacial maxima, which is the principal known historical barrier within southeastern Australia, has few detectable effects. Hydrological currents have apparently played only minor roles in determining the contemporary ranges of species or clades within them. Notably, species’ range limits in southern NSW are maintained despite the long-term flow of the East Australian Current. ITS-2 sequences were difficult to interpret phylogeographically as genetic divergence within species was absent for most taxa. All species had considerable numbers of low frequency COI haplotypes between which genetic divergence was shallow. Recently derived disequilibrium was revealed as an important driver of intra-species diversity for this gene. Inter-species comparisons favour demographic expansion over selective sweeps as explanations of the disequilibrium.