Desert Fishes Council, Death Valley, California, November 2006.
Phylogenetic patterns within Australian desert gobies.
P.J. Unmack & M. Adams
Phylogenetic patterns within Australian desert fishes remain relatively poorly known, although considerable research is underway to investigate the systematics and biogeography of this unusual fauna. A phylogenetic study was recently completed on one of the more interesting groups, the desert gobies (Gobiidae: Chlamydogobius) which have many parallels to the Cyprinodon pupfishes of North America. In both groups there are marine and freshwater species, they commonly occur as endemics in different spring complexes, they often inhabit harsh environments and as a result have extreme physico-chemical tolerances. The genus Chlamydogobius is thought to be endemic to Australia with one marine species C. ranunculus (Tadpole Goby) found across northern coastal Australia (sometimes in freshwater as well) and a radiation of five species within Central Australian Province (Lake Eyre Basin). Each species occurs within a distinct geographic area in tributaries of the largely dry Lake Eyre. Chlamydogobius squamigenus (Edgbaston Goby) mostly occurs in one small group of springs in the upper Cooper Creek catchment, C. micropterus (Elizabeth Springs Goby) occurs in one small group of springs in the middle Diamantina River catchment, C. japalpa (Finke Goby) occurs in the upper portion of the Finke River and is the only species found exclusively within riverine habitat, C. gloveri (Dalhousie Goby) occurs in Dalhousie Springs near the lowermost Finke River, and the last species, C. eremius (Desert Goby) is found in numerous small springs and creeks mostly to the west of Lake Eyre. We used the complete sequence of the mitochondrial cytochrome b gene and allozyme electrophoresis on 53 presumptive loci to examine species relationships. Results from each dataset broadly agree on species boundaries, with the exception of C. japalpa, as it was not resolved as distinct from C. eremius in the allozyme analysis. However, it was distinct in the cytochrome b dataset and can be easily morphologically distinguished. Within cytochrome b, most nodes had high bootstrap values (> 80), with C. ranunculus recovered as the basal member of the genus. The more geographically isolated and morphologically distinct species C. micropterus was basal within Central Australia, followed by C. gloveri. The remaining three species (C. squamigenus, C. japalpa, C. eremius) were all closely related which is consistent with the more recent isolation of their drainages as well as overall morphological similarity. The phylogenetic patterns observed are likely the result of an initial invasion of Chlamydogobius into Central Australia from northern drainages during Late Miocene or Pliocene during a wetter climatic phase. Once within the Lake Eyre Basin they were able to disperse widely, and due to their ability to live in small, isolated, harsh environments they were able to colonize a number of spring systems. As climate became increasingly arid, it progressively fragmented and isolated these populations, resulting in a phylogenetic pattern broadly consistent with the known climatic fragmentation of these drainages.