Systematics and phylogeny of the Tasmanian freshwater crayfish genus Parastacoides (Decapoda: Parastacidae)

The endemic Tasmanian freshwater crayfish genus Parastacoides is confined to the western parts of the State. The most recent review of the genus recognised only one species, consisting of three sub-species. Since that review, extensive collection in remote areas of Tasmania had been undertaken and the diversity revealed by these collections suggested the need for a review. This thesis presents a complete review of the systematics of the genus, investigating morphological, molecular and biogeographical aspects of the taxon. Two genera consisting of fourteen species are now recognised; suggested nomenclature, full descriptions, illustrations, distribution maps and keys are provided. Three species comprise the new genus Spinastacoides and 11 species comprise the new genus Ombrastacoides. The main diagnostic feature separating the two genera is the presence/absence of a terminal mesial spine on the uropod exopod. All species were found to be highly conservative morphologically, with few useful diagnostic characters. Paradoxically, a large degree of within-species plasticity was noted. Despite the high degree of morphological conservatism displayed, morphometric analyses confirmed that there was significant variation in shape between genera and species groups. Distributions of genera and species were mapped and discussed, and possible influences determining the distribution are discussed. Distinctive differences were noted in the distributional patterns of the two genera. The genus Spinastacoides occupies the south-western region, with each species having similar distributions of similar area. The genus Ombrastacoides occurs throughout the western half of the state, however it is absent from the much of the region occupied by Spinastacoides species. Ombrastacoides species have widely differing ranges, with some species having extremely restricted distributions. The main factor limiting the distribution of the two genera to the western regions of Tasmania appears to be a combination of rainfall and evaporation rate; the rate must be sufficient to retain a degree of burrow moisture through the dryer summer months. Molecular studies, involving allozyme electrophoresis, COI mtDNA and 16S mtDNA analyses, suggest that genetic distances between species are very high, and that the speciation events are ancient, occurring well before the Pleistocene glaciations, most probably during the Miocene. A study into the ecological niches occupied by the different species suggested that most species were generalists, able to exploit a wide variety of vegetation, substrate, temperature and altitude variables. Adaptive radiation could therefore be eliminated as a major determinant for the speciation and distribution of the species. A combination of ecological (the increasing aridity of the Australian climate, the vegetation turnover from C3 to C4 plants, the decrease in atmospheric CO2 levels) and vicariant events (glaciations, volcanic activity, the Australian mainland and Tasmania becoming separated by the formation of Bass Strait) occurring during the Miocene are suggested as causes of speciation. While some closely related sister-taxa clades are geographically based, overall the relationships between the phylogeny of these species and their geographic distributions are not straight forward, and some possible explanations are given. The sister-group relationship with South American and New Zealand taxa suggest the origin of the ancestral taxon during the Cretaceous, when these land masses were still connected. The origin was also most likely somewhere near the vicinity of the extant taxa.