American Society of Ichthyologists and Herpetologists, New Orleans, LA, July 2006.

Historical biogeographic patterns across multiple Australian freshwater fish groups.

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. Three freshwater fish groups, Craterocephalus, Melanotaenia and Nannoperca 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. This is due to the widespread presence of low drainage divides which may allow fishes to move across catchment boundaries during high rainfall periods without drainage rearrangement. The second is that vicariance in freshwater systems does not appear to be a powerful structuring force. Although vicariant events are occurring on a regular basis, the fish fauna may not be equally affected by these events due to differences in ecology and climate. 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.