Triton's trident: cryptic Neogene divergences in a marine clam (Lasaea australis) correspond to Australia's three temperate biogeographic provinces

Abstract

The southern coast of Australia is composed of three distinct biogeographic provinces distinguished primarily by intertidal community composition. Several ecological mechanisms have been proposed to explain their formation and persistence, but no consensus has been reached. The marine clam Lasaea australis is arguably the most common bivalve on southern Australian rocky shores and occurs in all three provinces. Here, we tested if this species exhibits cryptic genetic structuring corresponding to the provinces and if so, what mechanisms potentially drove its divergence. Variation in two mitochondrial genes (16S and COIII) and one nuclear gene (ITS2) was assayed to test for genetic structuring and to reconstruct the clam's phylogenetic history. Our results showed that L. australis is comprised of three cryptic mitochondrial clades, each corresponding almost perfectly to one of the three biogeographic provinces. Divergence time estimates place their cladogenesis in the Neogene. The trident-like topology and Neogene time frame of L. australis cladogenesis are incongruent with Quaternary vicariance predictions: a two-clade topology produced by Pleistocene Bass Strait land bridge formation. We hypothesize that the interaction of the Middle Miocene Climate Transition with the specific geography of the southern coastline of Australia was the primary cladogenic driver in this clam lineage. Additional in-depth studies of the endemic southern Australian marine biota across all three provinces are needed to establish the generality of this proposed older framework for regional cladogenesis.

Phylogeography of the Hypnea musciformis species complex (Gigartinales, Rhodophyta) with the recognition of cryptic species in the western Atlantic Ocean

“…Marine–terrestrial patterns of either phylo‐ or biogeographic concordance have also been observed for floristic composition in other parts of the world, such as western and southern Australia (e.g., Li et al. , Gurgel et al. , Colgan , Teske et al.…”

Commensal associations and benthic habitats shape macroevolution of the bivalve clade Galeommatoidea

“…Both developmental modes have free-living and commensal representatives. However, case studies on galeommatoideans have shown that direct developers can have extensive geographical ranges [29,61] and that indirect developers can be geographically quite restricted [62]. It is known that molluscan species with similar developmental modes can show drastically different population structures [63].…”

Differential adaptations between cold-stenothermal environments in the bivalve Lissarca cf. miliaris (Philobryidae) from the Scotia Sea islands and Antarctic Peninsula

“…Over time, distinct phenotypes can become genetically canalised, even when faced with moderate levels of gene flow (Knowlton, 1993;Schluter, 2009). This may be particularly true for brooding species where life history traits prevent genetic transfer between populations, as studied in the genus Lasaea (Crisp and Standen, 1988;Ó Foighil and Smith 1996;Li et al, 2013).…”