Phylogeographic structure in the gilgie (Decapoda: Parastacidae: Cherax quinquecarinatus ): a south‐western Australian freshwater crayfish

The gilgie ( Cherax quinquecarinatus ) is among the more widespread of the six endemic south‐western Australian freshwater crayfish species. In the present study, the phylogeographic structure of the gilgie was investigated across its distribution to determine whether patterns reflected those identified earlier in a co‐distributed congeneric, the koonac ( Cherax preissii ). Gilgies were sampled from 20 localities, a 412‐bp fragment of the cytochrome c oxidase subunit I mitochondrial DNA gene was amplified from 75 individuals, and allozyme variation was assayed at nine loci. As in the koonac, three geographically‐restricted lineages were identified: from the north‐western, southern coastal, and intermediate/south‐western regions. Phylogeographic breaks appeared to be congruent with those in the koonac. The extent of genetic differentiation among lineages was comparable to that in the koonac, suggesting temporal congruence of the historical events responsible for the observed structure. A relaxed Bayesian molecular clock suggested that the major clades and lineages in each species diverged in the Late Miocene–Early Pliocene (4.0–9.6 Myr ago), possibly resulting from increasing pulses of aridity. The retrieval of almost‐identical phylogeographic structure in two co‐distributed species suggests that biogeographic regions can be more accurately defined in south‐western Australia. With the geographic fidelity of these lineages, the present data also provide evidence of the translocation of a single individual from the north‐west to the south coast. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society , 2010, 101 , 385–402.