Mitochondrial DNA phylogenetic structuring suggests similarity between two morphologically plastic genera of Australian freshwater mussels (Unionoida : Hyriidae)

Abstract

In the Lake Eyre Basin, the Australian hyriid genus Velesunio is represented by three undescribed species, each of which are highly divergent genetically, but morphologically similar to Velesunio wilsonii (Lea 1859). A fourth species, Velesunio ambiguus (Philippi 1847), occurs not only in the Lake Eyre Basin but throughout much of eastern Australia, including the Murray-Darling Basin. In this study, we show that another hyriid, Alathyria jacksoni (Iredale 1934), which is sympatric with V. ambiguus, is genetically deeply nested within the Velesunio species complex, such that the genus Velesunio is paraphyletic with respect to A. jacksoni. Moreover, our mitochondrial phylogenetic reconstructions indicate that A. jacksoni is closely allied to one of the cryptic Velesunio species occurring in the Lake Eyre Basin, but distinct from V. ambiguus and the two other Velesunio species. These data suggest that the genera Alathyria and Velesunio are in need of revision. The shells of A. jacksoni and Velesunio spp. vary with local conditions and sometimes are difficult to distinguish. Our analyses also show that shell characters of these taxa do not closely match the phylogenetic data, and it appears that the traditional taxonomic emphasis on these plastic characters has obscured evolutionary relationships between these, and possibly other, Hyriidae.