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The systematics and zoogeography of the freshwater crayfish genus Engaeus Erichson (decapoda; parastacidae)
thesisposted on 2023-05-26, 20:16 authored by Horwitz, P
The taxonomy of the freshwater crayfish genus Engaeus has been investigated using the techniques of allozyme electrophoresis, multivariate morphometrics and classical taxonomy. The use of these three techniques allows an investigation of both genetic and morphological variation in the genus. It is proposed to synonymize 4 of the previously described species and to erect 14 new species, taking the total number of species in the genus to 34. Based on morphological characters, a partial key to the genera of the Parastacidae and a key to the species in the genus Engaeus is given. The description of each species includes a diagnosis, a description of an adult male and an adult female, a discussion of the morphological variation and comments on aspects of the species' life history. The genealogical relationships of closely related species have been determined from the distance data presented in the electrophoresis section. These relationships are supported with an analysis of ancestral and derived morphological character states, to result in a dendrogram depicting the phylogenetic relationships of the species in Engaeus and its allied genera. This dendrogram is compared to previous phylogenies proposed for the parastacids. In general terms the distribution of Engaeus can be described as conforming to the 'Bassian biogeographical region' in south-eastern Australia. Here it has been found to exhibit a high degree of regional endemism; for instance of the 34 species only 2 species occur in both Victoria and Tasmania. In Victoria, 20 endemic species have been recorded. A trend of high diversity and high endemism of the crayfish fauna has been found in highland regions, whilst low levels of both diversity and endemism are recorded for lowland regions. This is attributed to an increase in the number of available habitats in topographically diverse areas of the State. The situation in Tasmania, where 12 species are endemic, is somewhat more difficult to interpret. It seems that the western portion of the island, with its more predictable climatic conditions, can be characterized by broad distributional ranges of a few species, whilst the heterogeneous north-east of the island exhibits many species with reduced, often restricted, geographical ranges. Four modes of speciation are proposed. The fluctuating sea-levels in the Bass Strait region which accompanied successive glacial and interglacial periods are suggested as the major mechanism in the establishment of geographical barriers between populations. An absence in the literature of similar studies (on diverse monophyletic groups in the same area) prevents the examination of zoogeographical concordance. Further research is proposed to test the ideas presented in this thesis.
Rights statementCopyright 1986 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Appendix I (1) appears to be the equivalent of a post print version of an article published as: Horwitz, P., (1988), Secondary sexual characteristics of females of the freshwater crayfish genus Engaeus (decapoda, parastacidae), Crustaceana, 54(1), 25-32 Appendix I (2) has been removed for copyright reasons. It is a published article: Horwitz, P. H. J., Knott, B., 1983, The burrowing habit of the koonac, Cherax plebejus (Decapoda: Parastacidae), Western Australian naturalist, 15, 113-117 Appendix I (3) is a published article: Horwitz, P. H. J., Richardson, A. M. M., Boulton, A. 1985b, The burrow habitat of two sympatric species of land crayfish, Engaeus urostrictus and E. tuberculatus (Decapoda: Parastacidae), Victorian naturalist 102, 188-197. Appendix I (4) is a published article: Horwitz, P. H. J., Richardson, A. M. M., Cramp, P. M., 1985a, Aspects of the life history of the burrowing freshwater crayfish Engaeus leptorhyncus at Rattrays Marsh, north east Tasmania, Tasmanian naturalist, 82, July, 1-5 Appendix I (5) has been removed for copyright reasons. It is a published article: Horwitz, P. H. J., Richardson, A. M. M., 1986, An ecological classification of the burrows of Australian freshwater crayfish, 37(2), 237-242