Zoology - Theses
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ItemThe Australian freshwater malacostraca and their epizoic fauna( 1964)Because of their disjunctive distribution, the Parastacidae (Crustacea, Decapoda) and the Phreatoicoidea (Crustacea, Isopoda) have long been of considerable zoogeographic interest. The Phreatoicoidea are known from South Africa, India, Australia and New Zealand; the Parastacidae from Madagascar, New Guinea, Australia, New Zealand and South America. Of potentially great value, then, is a study of the epizoic fauna found closely associated with these fresh-water crustacea, and in some cases, sharing the disjunctive distribution. When new species of the peritrichous ciliate Lagenophrys were discovered on the cuticle of those crustacea, the opportunity was taken to initiate an investigation into zoogeographical implication of the distribution of a host-epizooid complex. The hosts were of established interest. Lagenophrys was of presumed interest because of low vagility during its dispersal phase, and because of the apparently high specificity of northern hemisphere members of the genus. In this thesis attention has been concentrated on the peritrichous epizooids. Although ideally a study should ultimately analyse the whole complex, the difficulties involved in such disparate taxonomies allowed of brief notes only on the other groups. Observations of the genus Temnocephala are included in the systematic section below but the other groups will be merely mentioned. Half the thesis is devoted to problems directly concerning the Parastacidae. For maximum value from the data on the epizoic fauna, precise determinations of host species were essential. In the course of investigation, it became clear that a review of Parastacidae systematics would be a prerequisite. (It will be seen that the Parastacidae form the most important group of hosts for the peritrichs investigated.) This situation arose partly from the lack of facilities at present obtaining in Australia for identification of the Parastacidae, and partly from ambiguities in the currently accepted systematics. These problems are posted in the section on Parastacidae, and their influence on problems of specificity is discussed in the final section.
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ItemFactors influencing egg survival in Aedes eggs with special reference to some Victorian species (Diptera: Culicidae)( 1962)Detailed information on the layers comprising the shell of Aedes eggs is important from an ecological point of view. The eggs in this genus are usually deposited above waterline in a variety of habitats which are subjected to period drying. They are especially adapted to those conditions and appear to withstand long periods of drought. These eggs very seldom hatch except under favourable conditions which occur when the breeding sites are inundated by rising water level during heavy rain or irrigational flooding. Thus the fact that these eggs which are primarily dependent on water for survival are able to withstand prolonged periods of desiccation is of particular significance. It would appear that this adaptation is the feature which ensures the continuance of the species in areas where such long periods of drought are common e.g. Mallee in Victoria. Thus a thorough knowledge of the chemical composition, structural morphology and development changes of the protective coverings of the shell in Aedes is a necessary pre-requisite for any ecological study of these species. As far as Aedes is concerned, little work has been accomplished in this area before. The eggs of these mosquitoes are able to remain dormant for a year or more (Christophers, 1960). During this dormancy a fully developed embryo is present within the egg. This is in contrast to the situation in grasshopper eggs, which may also remain viable for extended periods but in which the embryo is in an arrested stage of development (diapause). Because their embryonic development is complete, conditioned eggs of Aedes may hatch in a matter of minutes after sub-mergence. The term “conditioned” refers to previous exposure to environmental factors favouring a rapid and uniformly high incidence of hatching. It has been established that the removal of oxygen from the surrounding medium must occur before hatching takes place. Presumably in these high temperature regions this occurs very rapidly due to the activity of the microorganisms in the soil after precipitation. However, in addition to this need for a reduced oxygen tension during flooding, a pre-exposure to certain environmental conditions is essential to ensure an uniform and a high rate of hatching. These environmental factors which facilitate hatching vary with each species and have been collectively termed “conditioning” by Borg and Horsfall (1953) and Horsfall (1956). The failure to appreciate the conditioning process has been a serious handicap to work on the genetics and developmental physiology of species investigated for their medical importance.