Past and present patterns of connectivity among populations of four cryptic species of freshwater mussels Velesunio spp. (Hyriidae) in central Australia.

We examined genetic structure and levels of connectivity among subpopulations within each of four cryptic species belonging to the freshwater mussel genus Velesunio. We used allozymes and a fragment of the mitochondrial cytochrome c oxidase I gene to examine genetic variation in populations from isolated waterholes, belonging to four major inland drainages in eastern Australia. Based on evidence from other invertebrates in the region we predicted that, in each species, we would find evidence of historical connectivity among populations from different drainages. This was clearly not the case, as for the two species that occurred in more than one drainage there was evidence of both current and past restriction to gene flow. Moreover, given the potential for extensive dispersal of these mussels through the river systems during flood times via their fish hosts, we predicted low levels of genetic variation among populations from waterholes in the same drainage. Contrary to our expectations, all four species showed some evidence of restricted gene flow among waterholes within drainages. This suggests that either (a) mussel larvae are not produced during flood times, when their fish hosts would be free to move between waterholes, or (b) mussel larvae are attached to their hosts at these times, but the fish movement is limited between waterholes.