Zoology - Theses
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ItemAn electrophysiological study of muscle in tissue culture(University of Melbourne, 1975)
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ItemThe endocrine control of reproduction in the harlequin bug, dindymus versicolour (herr.-sch) (hemiptera : pyrrhocoridae)(University of Melbourne, 1972)The work presented in this thesis is an attempt to provide further insight into the endocrine factors which initiate and control the development of eggs in the female insect. It was therefore imperative that part of this study was directed towards an understanding of the neuro-endocrine system of the insect studied. One characteristic feature of the reproductive cycle of Dindymus is the prolonged and continuous copulation. Copulation is essential for the initiation of the vitellogenic cycle; interruption of copulation results in a retardation or cessation of vitellogenesis. Consequently, special attention was given to the manner in which copulation influenced the endocrine system.
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ItemEmbryonic diapause in the field cricket Teleogryllus Commodus(University of Melbourne, 1972)The mechanism of control of embryonic diapause in Teleogryllus commodus was investigated by experiments aimed firstly at studying the parental role in diapause determination and secondly, at analysing some of the biochemical changes associated with diapause initiation and termination in the egg. Implantation procedures were used to investigate the possibility that maternal endocrine effects, of the type demonstrated in the silkworm Bombyx mori, operate in Teleogryllus. Endocrine organs were transferred from diapausing T. commodus adult females to adult females of the non-diapausing T.oceanicus species. The organs implanted included the suboesophageal ganglion, brain, corpus cardiacum and corpora allata. The T. oceanicus females were mated with both T. oceanicus and T. commodus males, and the diapause characteristics of the eggs were assessed. The implants were shown to have no positive effect on diapause in the egg. However the experiments did reveal that the T. oceanicus ? x T. commodus ? hybrid has an embryonic diapause. This was contrary to the results of previous hybridization studies with these two species. It was in fact considered generally that diapause is absent in hybrids between diapausing and non-diapausing crickets. The presence of diapause in the T. oceanicus ? x T. commodus ? hybrid was confirmed in an experiment which compared the respiratory rates and morphological development of the hybrid and parent species. A genetical model proposed to fit this result has suggested that diapause in Teleogryllus is controlled by both a cytoplasmic factor produced by the parent female and by factors determined by the embryonic genome. Biochemical investigations were aimed at elucidating the nature of these factors. It was shown that rises in the level of free amino acids associated with proteolytic activity occur at diapause initiation and during diapause development in T. commodus. The rise at diapause initiation was shown to precede water absorption and is likely to be associated with this activity. The occurrence of proteolysis during diapause development would seem to be of significance to the process of diapause termination. Diapause development was shown to involve changes in the acrylamide patterns of soluble proteins and a 20% reduction in the amount of lipoprotein. It was shown to be accompanied by an increase in the in vitro activity of a phenoloxidase enzyme. The activity was dependent on the pH, molarity and lipoprotein concentration of the homogenate. No role for this enzyme in the process of diapause termination could be suggested. A proposal for a biochemical mechanism of diapause is made. It is suggested that diapause is initiated by the inactivation of an enzyme or enzymes essential for embryonic growth beyond the diapause stage. Diapause development is then considered as a process of activation of this enzyme (enzymes) either by the removal of an inhibitor or the production of an activator.
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ItemA comparative study of the flora and fauna of exotic pine plantations and adjacent, indigenous eucalypt forests in Gippsland, Victoria( 1978-01)The introduction and establishment of a new and markedly different environment within a long established natural system provides an excellent opportunity to study the principles of adaptation and colonisation by native species. In Australia, an example is furnished by the conversion of large areas of native eucalypt forests to mono-cultured plantations of Monterey Pine (Pinus radiata). The principal aim of this study was to assess which species of native mammals, birds and higher plants are able to utilise or occupy such plantations. Successional aspects of community structure, and colonisation in pine forest systems, were investigated by considering stands of different ages. A variety of adjacent native eucalypt forests provided controls and indicated the range of potential colonisers. Various habitats in both forest types were studied with regard to potential nest sites and availability of food, in order to determine those habitats most favourable for mammals and birds. The effect, on wildlife, of clearing eucalypt forests, but leaving forest remnants along gullies, was also assessed.
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ItemLife-history strategies of five species of intertidal limpet( 1977)The life-long strategies of five species of intertidal limpet, Cellana tramoserica, Notoacmea petterdi, Patella peroni, Patelloida alticostata, and Siphonaria diemenensis, which occur on the same shore but in different tidal zones, are considered in relation to their different environments. Attention is focused upon reproductive effort, which is defined as the percentage of assimilated energy devoted to reproduction, and which is measured for each species by using annual energy budgets. Environmental and demographic factors, which previous workers have suggested may have important influences on the level of reproductive effort, are investigated. In particular, interspecific differences in reproductive effort are compared with differences in the availability of food resources, differences in the magnitude of density-independent causes of mortality, differences in adult mortality rates and differences in extrinsic adult mortality rates (i.e. the adult mortality rates that would occur in the absence of expenditure of energy in reproduction.) The results of the present study indicate that reproductive effort is correlated with the availability of food resources, but that the primary determinant of the optimum level of reproductive effort is the rate of extrinsic adult mortality.
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ItemThe evolutionary significance of postmating isolation in anuran amphibians( 1974)Levels of intertaxon genetic incompatibility were determined within three south-eastern Australian amphibian species groups: the genus Ranidella; the Geocrinia laevis complex; and the Litoria ewingi complex. These groups include, wide-ranging taxa in which an assessment of regional differentiation could be made, as well as a variety of intertaxon interactions ranging from broad intergradation to extensive sympatry. Particular emphasis was placed on analysis of narrow zones of interaction between taxa in an attempt to determine the relative importance of the various types of reproductive isolating mechanisms outlined by Littlejohn (1969). The major method employed in these studies was in vitro artificial hybridization. Data derived from this investigation were combined with other available information on aspects of reproductive isolation and general biology of the included taxa, both to assess the significance of reproductive isolation, and to determine phylogenetic relationships and patterns of speciation within the three species groups. The wide-ranging taxa show a high level of genetic uniformity throughout their ranges, suggesting that levels of organization higher than local populations (i.e. biological species) exist in nature. The operation of two fundamentally different kinds of potential postmating isolating factors is suggested. Firstly, a significant level of intrinsic postmating isolation between species, where present, results in their effective and irreversible separation. However, it was found that cognate taxa were generally not characterized by high levels of genetic incompatibility. Secondly, ecological differences between interacting taxa, arising from adaptations to discontinuous, heterogeneous habitats, could provide significant isolation which, in terms of natural selection, has the same effect as intrinsic postmating factors. Premating isolating mechanisms are clearly highly adaptive in terms of reproductive efficiency and success. However the adaptive significance of premating isolation is manifest only in situations where selection acts against individuals which mismate. Hence isolation between interacting taxa dependent solely on premating isolating mechanisms is tenuous and likely to break down. It is proposed that future research on the mechanisms of divergent evolution should be directed more towards detailed studies of extensively sympatric cognate species, particularly their ecological interactions, and less towards the genetic aspects of hybrid zones.
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ItemEcological and physiological studies of Sminthopsis crassicaudata (Marsupialia : Dasyuridae)( 1976)This study aimed to identify the major adaptations enabling a small insectivorous marsupial, Sminthopsis crassicaudata, to inhabit a variety of open grassland and desert environments. A series of integrated investigations of behaviour, reproduction and physiological ecology was carried out. S. crassicaudata displays a "drifting home range" pattern of social organization, there is little evidence of territorial behaviour, and individuals are solitary during breeding but gregarious in autumn and winter. In both arid and comparatively mesic habitats, breeding occurs from late winter until early autumn; there is no evidence that opportunistic breeding takes place in late autumn or early winter. During the breeding season each female attempts to raise two litters; few individuals of either sex breed in more than one season. All these characteristics are interpreted as adaptations to both long-term (seasonal) and short-term variability in food supply. S. crassicaudata can survive without drinking water when fed on a diet of insects. This independence is made possible by the high water content of the food, and not by physiological restriction of water loss as is seen in granivorous desert-dwelling rodents. Similarly, the energy metabolism of S. crassicaudata shows no evidence of specific adaptations to aridity. The apparent physiological specializations - brief diurnal torpor and fat storage - seem to be related to the problem of fluctuation in food supply, and not to aridity as such. Thus the biology of S. crassicaudata is interpreted as reflecting specific adaptation to variability in food supply; this variability seems to be the major problem facing a nocturnal insectivore inhabiting open environments.