The molecular systematics of Leiopotherapon unicolor (Günther, 1859): testing for cryptic speciation in Australia’s most widespread freshwater fish

<i>Leiopotherapon unicolor</i> is the most widespread freshwater fish species in Australia. A comprehensive allozyme and mitochondrial DNA 16S rRNA data set was assembled from 141 specimens of <i>L. unicolor</i> collected Australia-wide in order to test for cryptic speciation in this far-ranging species. Surprisingly, little genetic diversity was observed within <i>L. unicolor</i> and provided no evidence for the existence of cryptic species within this lineage. In contrast, a small sample set of <i>L. aheneus</i> used as the outgroup showed two highly divergent haplotypes strongly suggestive of cryptic speciation. <i>L. unicolor</i> has a number of ecological and life history attributes that may explain the lack of significant genetic divergence over substantial geographical distances. The occurrence of other widespread fish and crustacean species that also display only limited genetic diversity indicate that climate conditions more favourable to dispersal across central and northern Australia than is suggested by the extent of present-day aridity have occurred in the relatively recent geological past.<br />