Australian Society for Fish Biology, Fremantle, Australia, June 2009.

Comparative phylogeography of Australian freshwater fishes

P.J. Unmack

Freshwater aquatic systems are different biogeographically to other habitat types due to their different distribution and connectivity patterns. Because obligate freshwater aquatic organisms are only able to move via direct connections between habitats, drainage basins greatly limit opportunities for movement due to their isolated nature. Potential physical connectivity between drainage basins is largely limited to two factors: changes in sea level, which allow drainages to coalesce when sea level falls; and drainage rearrangements, which result in changed catchment boundaries. Several freshwater fish groups were chosen for phylogeographic analysis based on their broad ranges, number of species, geographic overlap and to provide maximum coverage of Australia. When phylogenetic patterns for each fish group were combined, there was little congruence in their patterns of divergence across Australia despite a high degree of co-occurrence. Two factors are proposed to explain this result. The first is that dispersal across freshwater biogeographic barriers may be more common than previously thought. The second is that vicariance in freshwater systems does not appear to be a powerful structuring force. Over-arching biogeographic hypotheses are inadequate to explain the independent histories of each group. My research adds to the growing body of literature that suggests independent biogeographic patterns are common. Therefore, finding broader explanations for patterns may be the exception rather than the rule.