Date of Award
Bachelor of Science Honours
School of Natural Sciences
Faculty of Computing, Health and Science
Dr Pierre Horwitz
The south-west of Western Australia is home to an endemic genus of obligate burrowing freshwater crayfish, Engaewa Riek. Riek (1967) first described three species within this genus and later Horwitz and Adams (2000) described an additional two species. Of the five species which are currently recognised three species (E. reducta, E. pseudoreducta and E. similis) form a species complex; the reducta complex. The work ofRiek and later Horwitz and Adams are the only two reviews of note dealing with this genus despite a publication by Crandall, Fetzner, Lawler, Kinnersley and Austin (1999) which suggests that Engaewa may be the sister taxon to all other Australian genera. Adding further impetus to this work is the listing of two species within the complex as being critically endangered and endangered (E. pseudoreducta and E. reducta respectively). A major concern that arises regarding the conservation status of these crayfish is the impact that their loss would create on the swamp systems that they inhabit as they are probable keystone species. As such a review of the systematics of the reducta complex was warranted to further clarify the number and distribution of species with the intention of facilitating the formation of an interim recovery program which will ensure not only the ongoing survival of this crayfish genus as a whole but also that the maximum genetic diversity is maintained. The review of the reducta complex was performed using morphological, morphometric and molecular techniques. In this regard it followed the format of the most recent review of the genus (Horwitz & Adams, 2000) by combining typical crayfish morphological characters with the results of allozyme electrophoresis in order to provide a robust taxonomic treatment of the subject. The combination of morphology and molecules is particularly useful in crayfish studies as many characters have the potential to be plastic. In addition to these techniques habitat data was analysed in an attempt to relate habitat variables to key morphological characters. Unfortunately the habitat data was unable to be applied to the systematics but it was used to create a basic profile of the habitat occupied by Engaewa. The combination of key morphological characters, in particular the inflated portion of the sternal keel and the setation pattern of the chelae, and allozyme profiles for two known useful genetic markers did however provide strong support for the recognition of the three current species. The data from this study also raises the possibility that further division of the complex may be warranted. Future work needs to be concentrated on the interface of the current species boundaries with the populations within Spearwood Creek and around Treeton State Forest a priority. The application of DNA based molecular analysis combined with further morphological treatment of the subject should provide the best resolution of the systematics of this complex.
Burnham, Q. (2005). The systematics of the reducta complex of the burrowing freshwater crayfish Engaewa Riek. https://ro.ecu.edu.au/theses_hons/1030