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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ItemNo Preview AvailableStudies in population genetics(University of Melbourne, 1959)Population genetics and. population dynamics have formed two distinct avenues of approach to a field of study which has become increasingly important over the last thirty years. Each has proved highly susceptible to mathematical analysis and to quantitative, rather than merely descriptive, treatment. It is, however, surprising to find that relatively little has been done to unite these two aspects of population biology, while in each theoretical work has tended to outstrip the small foundation provided by the observations so far recorded in the literature. Thus Birch (1957.P.217) was led to say... "I am quite sceptical of the predictive value of such mathematical models as have to date been proposed for natural populations". More serious still is the fact that the attempt to fit slender experimental data to such models has often blinded the experimenter to the possibility that factors of importance other than those considered in his model may contribute to the observed properties of the population. In particular, there has been little attention given to the genetic control of the form and rate of population growth; the work of Buzzati-Traverso (1955) was the first major experimental analysis to produce useful results along these lines. Much of the work on Drosophila populations has been done on small breeding groups which have been assumed to have reached an equilibrium density, although it seems likely that laboratory populations of Drosophila develop in the same way as those of Lucilia (Nicholson, 1954 and earlier papers), in which the population number fluctuates quite widely about a mean, not absolute, "equilibrium" level. Further, the number of individuals in the populations has not usually been determined with accuracy, so that it has seldom been possible to study small changes in population size. Preoccupation with "competition" experiments involving oligogenic markers has led even experienced workers to ignore the importance of modifying influences, particularly polygenic systems, associated with the genetic background. In this connection Buzzati-Traverso (loc.cit.) stated: "The fact is that the change in frequency of a single gene (or chromosome) during a number of generations means that the individuals carrying its allele will produce more or fewer adult offspring in the next generation than the individuals not carrying it. The factor which is decisive for changing frequency is a "productivity differential" involving of necessity the whole genotype and not one gene alone, for the latter will have different survival values in different genetic milies. Some extreme mutants, like those mostly used in laboratory experiments, may affect specifically the productivity of its carriers to such an extent as to make the effects of the rest of the genotype and of interactions of the mutant with it insignificant. But under natural conditions the commonest ease is very likely that of 'small* mutants where the natural selection mechanism probably involves many genes at one time" Even in the case of 'extreme' mutants erroneous or unsupported conclusions have been published (see later discussion of the relative adaptive values of the alleles at the white locus of Drosophila given by Merrell & Underhill, 1956); while in other instances over-emphasis of one particular factor has often prevented a balanced statement of the factors operating in laboratory population experiments. The discovery of selective mating in Drosophila, for example, resulted in the application of mating test results to population cage results without regard to other factors which might be causing the observed gene frequency changes. The work of Nicoletti & Solima (1956) and Morpurgo & Nicoletti (1956), amongst others, has passed largely unnoticed, although these authors adduced considerable evidence to support their view that selective mating is in fact not a controlling factor in laboratory cage competitions even where it can be demonstrated to occur in mating tests of the genotypes involved. In the same way, a sharp distinction has not always been made between the overall adaptive value of a genotype in a particular environment. The differential migration rates reported by liar land & Jackson (1958) under the title �Advantage of the white eye mutant of Drosophila melanogaster over the wild type in an artificial environment" provides an instance of such confusion. The only real measure of "advantage" or "superiority" is the relative contribution of a genotype to the gene pool of the succeeding generation, but these authors mention no breeding experiments at all. It is, however, clear that they have identified one of the factors which might be of importance in determining the frequency of white relative to that of its wild type allele in populations maintained in a particular environment. The main object of the present work has been to investigate further the relation of the genetic structure of a population to its rate and type of growth. Some attention has been given to problems of the sex-ratio and to change in gene frequency; in each case the underlying mechanisms have been studied. Emphasis throughout has been placed on the determination of the relative importance of the possible component factors under conditions of intense competition such as those found in population cage experiments.
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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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ItemSystematics of the family Octopodidae (Mollusca:Cephalopoda) of South-Eastern Australia( 1988)The systematic of the inshore, benthic octopus of south-eastern Australia are examined. An historical survey of octopods from the region is followed by accounts of nominal species now recorded from waters of south-eastern Australia. Three genera and nine species are described and illustrated: Octopus australis, O. maorum, O. pallidus, O. superciliosus, Hapalochlaena maculosa, Grimpella thaumastocheir, plus three species of Octopus new to science. For each species, a study of external morphology and internal anatomy, type details, and distributional information, are included. Two species previously described from south-eastern Australia are reduced to synonymy: Octopus flindersi and O. duplex. Three species previously recorded from the region are excluded from the fauna: O.filamentosus, O. membranaceus and O. microphthalmus. A key to identification of valid species of octopus from south-eastern Australia is provided. The octopod fauna of the region comprises a high proportion of endemic species. Information on biogeography, and on affinities of some taxa with the fauna of New Zealand, is outlined.
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ItemThe evolution and ecology of the Gadopsis marmoratus complex( 1986)The Family Gadopsidae is the only family of fishes in South-eastern Australia which is both endemic to this region, and strictly confined to fresh water. Although several species of Gadopsis have been proposed, prior to the commencement of this study only one species, G. marmoratus Richardson, was formally recognised. This species was known to exhibit considerable geographic variation in morphology, colouration patterns, and size; and it had been suggested that the taxonomy of the genus was in need of review. This study is an attempt to: (i) determine the number of species in the, G. marmoratus complex; (ii) assess the relationships between G. marmoratus and any additional taxa in the complex; (iii) Formulate a biogeographic hypothesis to account for the geographic distributions and phylogenetic relationships of the taxa in the G. marmoratus complex; and, (iv) examine ecological characteristics of a population of Gadopsis from each side of the Great Dividing Range in Victoria. Analysis of meristic variation revealed that two sympatric taxa of Gadopsis were present in north-eastern Victoria. No evidence of hybridization between these taxa was found. The two taxa have different numbers of spines in the dorsal fin, and the specific status of the taxon with only two spines in the fin was recognised by the formal description of G. bispinosus Sanger. By adoption of an evolutionary species concept, and using univariate and multivariate statistical analyses of meristic variation, it was shown that G. marmoratus was comprised of two divergent taxa. It was proposed that these taxa be recognised as separate species, and for the purposes of this study are referred to as northern G. marmoratus and southern G. marmoratus. Multivariate statistical analyses of morphometric variation supported the proposal to recognise northern G. marmoratus and southern G. marmoratus as separate species. Electrophoretic analysis of protein variation also supported the recognition of northern G. marmoratus and southern G. marmoratus, and confirmed that hybridization was not occurring between G. bispinosus and northern G. marmoratus. The level of genetic divergence between northern G. marmoratus and southern G. marmoratus was less than that between both of these taxa and G. bispinosus. This result was interpreted to indicate a close phylogenetic relationship between northern G. marmoratus and southern G. marmoratus, and supported the relationships suggested by the phenetic analysis of meristic and morphometric variation. A biogeographic hypothesis to explain the geographic distributions and phylogenetic relationships of the three taxa was proposed. The ancestry of the Family Gadopsidae has been the subject of some dispute, and the alternative views on this subject were critically reviewed. Support was found for a basal percoid relationship for the family, and this result suggested that Gadopsis may have been of Gondwanan origin. The freshwater life-cycle of all the members of the family was interpreted as further support for a freshwater origin for Gadopsis. Several ecological characteristics of a population of G. bispinosus from the King Parrot Creek and G. marmoratus from the Yarra River system were compared. Gadopsis bispinosus in the King Parrot Creek is a small, lightly-built, short-lived species compared to G. marmoratus from the Yarra River system. The two species were found to have similar reproductive biologies. The discovery of additional species of Gadopsis has created the need for further examination of the evolution and ecology of the G. marmoratus complex, and suggestions for such further study are included at the end of this study.
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ItemThe feeding and breeding biology of the sacred ibis Threskiornis aethiopicus in southern Victoria( 1984)This study aimed to elucidate the major selective factors affecting the biology, and particularly the breeding ecology of the Sacred Ibis (Threskiornis aethiopicus) in Australia. A comparative study of the breeding ecology of the Family Plataleidae in Australia was undertaken to define the ecological niche of the Sacred Ibis. The Australian ibis and spoonbills have very similar breeding ecology to their conspecifics and congeners elsewhere in the world. However, the breeding success of Australian birds appears to be limited by food supply whereas, in African members of the Family, for example, breeding success is limited by predation. In Australia, Sacred Ibis exhibit two broad responses to their environment: some populations showed adaptations in their breeding to an unpredictable environment; and, other populations have developed complex breeding strategies that are dependent on a highly predictable set of environmental conditions. In unpredictable environments, Sacred Ibis do not breed regularly but rather breeding is closely tied to the variable environmental conditions; the ibis move away from the breeding site when the area dries out. In unpredictable environments, clutch size is adjusted to the conditions and the ibis may employ multiple brooding. Where the environment is much more predictable, Sacred Ibis breed on a very regular cycle. In these environments, ibis are highly sedentary and clutch and brood size and multiple brooding are adjusted to maximise seasonal reproductive success, that is, Sacred Ibis raise fewer offspring per brood than the apparent maximum number possible as a trade-off against raising more broods in each breeding season. The timing and duration of the breeding attempts has had a major effect on the mating system. Sacred Ibis are essentially monogamous but one case of apparent polygyny was found. The mating system is also characterised by a high rate of promiscuous copulation and changes of mate between breeding attempts. The roles of male and female in post-fledging care of young and costs/benefits to life-time fitness are discussed. The selective factors maintaining colonial nesting are reviewed and the single most important evolutionary pressure affecting the breeding ecology of the Sacred Ibis is finding food; predation was shown to be unimportant.