Molecular phylogenetic analysis of 28S rDNA supports a Gondwanan origin for Australasian Hyriidae (Mollusca : Bivalvia : Unionoida)

The Hyriidae (Mollusca: Bivalvia: Unionoida) have a disjunct distribution, occurring on South America, Australia, and New Zealand. Most previous macro evolutionary studies of the Hyriidae pre-dated widespread acceptance of bot h continental drift and phylogenetic systematics. For this study, we applie d molecular phylogenetic techniques to test the hypothesis that the observe d disjunction of Australasian hyriids across the Tasman Sea is due to the d isintegration of Gondwanaland (>80 million years ago). We sequenced a fragm ent of 288 rDNA for representative hyriid Velesunionini (Australia), Hyride llini (Australia and New Zealand), and Hyriinae (South America) and for out groups belonging to the unionoid families Margaritiferidae and Unionidae. T he topology of the single 288 tree [i.e., (Margaritiferidae, Unionidae, (Ve lesunionini, (Hyridellini, Hyriinae)))] recovered by both maximum parsimony and maximum likelihood did not support a monophyletic Australasian clade, and the branch lengths were consistent with Mesozoic vicariance. We also ac quired COI sequences for the Australian subset of mussels to corroborate th e 28S branch lengths. Our results suggest that (1) the Hyriidae pre-date th e break up of Gondwanaland and (2) the New Zealand Hyridellini are relies r ather than colonizers. Alternative long-distance dispersal hypotheses are d iscussed in the context of our results, historical geology, and mussel life history.