Science Collected Works - Theses
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ItemThe value of zoos : a quantitative assessment of the prevailing paradigm(University of Melbourne, 1998)The roles of zoological gardens in modem society is controversial. Zoos or 'menageries' of the past were for human entertainment. Animals did not behave like those in the wild and thus portrayed distorted images of wildlife. Under increasing pressure from welfare organisations (hereafter referred to as animal liberationists) and conservationists, the role of zoos is evolving. The release of 'The World Zoo Conservation Strategy' (WZCS) (International Union for Directors of Zoological Gardens (lUDZG) / Captive Breeding Specialist Group of lUCN/SSC (CBSG), 1993) articulated the commitment of modem zoos to play a role in species and habitat conservation, education, research, and recreation. Education is an essential role of modem zoos (lUDZG/CBSG, 1993) and it relies on zoos displaying animals that represent those in the wild. This study aimed to examine the status of zoos in Australia and New Zealand, with an emphasis on the modem zoos' aim of education (lUDZG/CBSG, 1993; Appendix A). It assessed a range of captive environments. These included 'typical' metropolitan zoos and the more modem approach to animal management represented at Victoria's Open Range Zoo at Werribee (VORZ). Visitors to the latter view savanna animals in more 'natural' surroundings during a safari tour which takes them amongst the animals. The educational value of exhibits was assessed by measuring animal behaviour and school students' perceptions of the animals. This employed a model zoo species from a savanna habitat; the Plains or Burchell's Zebra Equus burchelli. More general visitor attitudes to zoos and conservation were also investigated. The low intensive management of animals at VORZ allowed a large degree of 'natural' behaviour to be displayed, evident through the social organisation and behaviour, group dynamics, time budgets, and night behaviour of the animals. Hence this population potentially provided a valuable educational resource. In contrast, the behaviour of zebras in most metropolitan settings was characterised by unnatural time budgets (particularly feeding times), high levels of aggression, unnatural mare / stallion relationships, and restricted behavioural repertoires of stallions. These settings provided the animals with little control over their behaviour, which was largely influenced by a number of exhibit and husbandry characteristics. This indicated little potential educational value of the metropolitan animals and poor animal welfare. The VORZ exhibit, while more successful than Royal Melbourne Zoo (RMZ) at representing the 'real' animal and simulating an African savanna for students, did little to promote positive attitudes towards wild animals and their conservation, and to provide accurate knowledge of wild animals. A number of factors potentially limiting the educational value of the VORZ exhibit were discussed, including students holding traditional preconceptions of captivity, and the age of students. Zoo exhibits, irrespective of how 'natural' they are, may have limited educational impact if not complemented by appropriate educational aids. The RMZ exhibit did little to enhance student knowledge. It played a more traditional role, with evidence of students perceiving the animals as the 'exhibit', and the animals and their surroundings as 'unnatural'. Hence the RMZ exhibit did not play an educational role. Visitors to VORZ and RMZ largely supported the roles of zoos in educating visitors, helping conserve threatened animals, and providing a modern approach to animal management. VORZ was more successful than RMZ at promoting positive attitudes towards conservation and the role of zoos in conservation. Additionally, VORZ was perceived as a more appropriate environment for practicing conservation, through education and breeding threatened animals. Traditional attitudes towards zoos were also evident by visitors to both zoos. The present study suggested that open-range zoos, such as VORZ, are a positive step towards meeting the standards set by both the world zoo community (lUDZG/CBSG, 1993) and animal liberationists (World society for the protection of animals (WSPA) / The Born Free Foundation (BFF), 1994). However appropriate educational aids, such as the tour guide commentary at VORZ, may be essential to the value of 'naturalistic' exhibits. The contribution that metropolitan zoos can make to conservation, through exhibiting non territorial equids such as Plains zebras, is negligible. Typical' metropolitan zoos of today may have little potential to be education facilities, and must accept their current role as primarily entertainment. Zoos committed to increasing their conservation roles need to do more than simply develop more 'natural' exhibits. This study supports the need for specialisation of exhibits (lUDZG/CBSG, 1993; Chapter 1), such as sanctuaries for threatened species, native wildlife parks and open-range zoos. Metropolitan zoos need to improve educational tools for visitors, and to re-assess the purpose of exhibited species with respect to education. They must present an environment that evokes learning in an entertaining way. Recommended animal management and educational aids for all zoos committed to playing a role in conservation education are detailed, with particular emphasis on enhancing the educational value of exhibiting non-territorial equids.
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ItemSuperoxide production, hypersensitive response and phytoalexin accumulation during interactions between tobacco and phytophthora isolates(University of Melbourne, 1998)Plant and animal cells challenged by pathogens undergo an oxidative, rapidly release active oxygen species (AOS) at the cell surface. Active oxygen species, including the superoxide anion and hydrogen peroxide, are involved in a range of environmental responses in plants, although their precise role in disease resistance remains unclear (Low and Merida 1996; Sutherland 1991). The aim of this study is to examine the relationship between superoxide release and plant disease resistance responses, including hypersensitive cell death and accumulation of the sesquiterpenoid phytoalexin, capsidiol, in infected tobacco cell suspension cultures. Preliminary studies have shown that race-cultivar specificity in whole plants is retained in suspension cultures (Able et al 1998). Suspension cell cultures of the near isogenic N. tabacum cultivars Hicks (susceptible) and NC 2326 (resistant) of this cultivars maintained on MS liquid medium at 24�C, were inoculated with zoospores of the Black Shank pathogen Phytophthora parasitica var. nicotianae and the non-host pathogen Phytophthora palmivora. Inoculated suspension cells were examined at regular intervals from inoculation until pathogen sporulation in compatible interactions (approximately 30 hours). Superoxide release was monitored by staining with nitroblue tetrazolium (NET) for 15 minutes before each observation. Inhibition of staining by superoxide dismutase or Mn(III)-desferal, indicates stain specificity for the superoxide anion. Phytoalexin accumulation was monitored using gas chromatography, and cell viability was monitored using hypertonic red staining. Cell suspension cultures of N. tabacum respond to inoculation with incompatible strains of Phytophthora parasitica var. nicotianae or Phytophthora palmivora by rapidly releasing the superoxide anion in a zone surrounding the infection court. Superoxide release, indicated by SOD-inhibited NET reduction, is more intense in incompatible or non-host interactions than in compatible interactions. Later defence responses in cell suspension cultures, including cytoplasmic aggregation, nuclear migration, hypersensitive cell death, deposition of lignin and callose and phytoalexin accumulation, are also more rapid and intense in incompatible interactions. This hypothesis was tested by blocking superoxide release using the naturally- occurring enzyme, superoxide dismutase (SOD), or its analogue, Mn(III)-desferal. When present during attempted penetration and host colonisation, both suppress NET staining and capsidiol accumulation. SOD is less active than Mn(III)-desferal, possibly because its size excludes intimate contact with the plant cell membrane, the putative site of superoxide release. This work supports the hypothesis that superoxide release plays a role in the activation of defence responses, possibly through its ability to cause host cell membrane damage, leading to hypersensitive cell death and other responses. Superoxide release appears to be a key link in the signalling cascade leading to the elicitation of phytoalexins and other defence responses in this interaction. Further studies will examine the mechanism by which superoxide release elicits host defence responses.
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ItemThe evolution of cryptomonads and chlorarachniophytes(University of Melbourne, 1998)Cryptomonads and chlorarachniophytes are unicellular algae whose plastids are associated with a miniature nucleus called the nucleomorph. Both groups have acquired the ability to photosynthesise by engulfing and retaining a eukaryotic endosymbiont with a plastid. The nucleomorph is the highly reduced nucleus of the photosynthetic endosymbiont. Evolution and phylogeny within cryptomonads has not been well studied using molecular techniques. An 18S ribosomal ENA phylogeny of cryptomonads is presented here (chapter 2) . Cryptomonas sp. ?, the model organism for studies of cryptomonad plastid evolution and cell biology, is also characterised and confusion regarding its identity resolved (chapter 3). Although cryptomonads and chlorarachniophytes habour a eukaryotic endosymbiont with a plastid, the nucleus of this endosymbiont (the nucleomorph) does not appear to contain a complete complement of genes for photosynthesis-related proteins. Instead these genes are thought to have relocated to the host nucleus. I demonstrate that cryptomonad and chlorarachniophyte light-harvesting complex proteins are encoded in the host cell nucleus and are apparently targeted to the plastid. The plastid targeting mechanism of cryptomonad and chlorarachniophyte light-harvesting complex proteins is investigated (chapter 4). The possibility that chlorarachniophytes have host-encoded endosymbiont tubulins is also examined (chapter 5)
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ItemDevelopmental biology of the pollen wall in Arabidopsis(University of Melbourne, 1998)By selectively removing individual genes in mutant plants, the processes involved in pollen development can be dissected and characterised. Arabidopsis thaliana seeds were mutagenised by various EMS (ethylmethane sulfonate) concentrations and various exposure times. The Ml Arabidopsis plants were grown and M2 seeds of each line were collected and stored. Some M2 seeds were sown for M2 screening. About 10,000 M2 plants were screened for ms (male sterile) mutants and about a hundred ms mutants were found. Some of them were selected for light and electron microscopical analysis of pollen wall development. Several ms mutants, ms5, ms9 and ms12, have already been partially characterised by colleagues and this work reinvestigated these with a focus on exine development. From ultrastructural analysis, all the mutants characterised in this study were classified according to aberrations in exine development: 1. Thin exine mutants, which have very thin exines compared to those of wild type; 2. Primexine mutants that have defects in exine development and produce no mature pollen or rarely a few exceptionally large pollen grains; 3. Other exine mutants that develop exines with incomplete or abnormal sculpture. These mutants have been ordered according to their aberration time in Chapter 8. A male sterile mutant, ms5, was found to be a pollen wall mutant. The promoter of the mutant gene has previously been fused with a GUS reporter gene and transformed into wild type plants. Here, expression of the gene was determined with a GUS enzyme assay. This study further explained the important roles of both tapetum and pollen cytoplasm in exine development. The new mutants developed here did not develop pollen with a complete exine structure because either the cytoplasm or tapetum had defects in it. Characterising genes involved in exine development may enable future biosynthesis of sporopollenin which is remarkable for its resistance to both physical and enzymic degradation. The characterisation of pollen wall mutants produced in this study gave a clearer understanding of the processes involved in the formation of the wall in wild type pollen. A proposed model detailing the ultrastructural changes in pollen wall development is also presented here.
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ItemCuticular hydrocarbon mimicry of the ant Oecophylla smaragdina by the salticid spider Cosmophasis bitaeniata(University of Melbourne, 1998)Social insects use cuticular hydrocarbons to differentiate between species, but the evidence that cuticular hydrocarbons are used to differentiate between non-nestmate conspecifics is inconclusive. The salticid spider Cosmophasis bitaeniata is a myrmecophile that lives within and on the arboreal nests of the green tree ant Oecophylla smaragdina. Remarkably this spider preys on the larvae of its highly territorial and aggressive host. Gas chromatography and mass spectrometry reveal that C. bitaeniata mimics the cuticular hydrocarbons of O. smaragdina. Recognition bioassays involving the extraction of cuticular hydrocarbons from ants and spiders, the transfer of these substances to discs of filter paper, and the behavioural response of foraging major workers, reveal that the cuticular hydrocarbons of spiders appear to be chemically �invisible� to foraging major workers. While the cuticular extracts of non-nestmate workers are attacked by foraging workers, those of nestmates are given attention that is not aggressive. These data together with additional bioassays reveal that the qualitative chemical resemblance of ants by spiders, combined with the spiders ability to avoid contact with major workers, function to avoid detection by major workers of O. smaragdina. The relative proportions of the cuticular hydrocarbons of social insects may constitute a colony recognition cue that workers use to differentiate between nestmate and non-nestmate conspecifics. Hydrocarbon proportions are also used to differentiate between different castes within a species. The relative proportions of the cuticular hydrocarbons of spiders are colony-specific, with the variation in the hydrocarbon proportions of spiders within a colony being less than the variation in hydrocarbon proportions between colonies. Major workers of O. smaragdina also have colony-specific cuticular hydrocarbon proportions. However, these proportions are not mimicked by spiders. This suggests that spiders may mimic either the minor workers or the larvae of their hosts. Recognition bioassays involving the capture of larvae in the presence of major and minor workers and the behaviour of ants and spiders when combined with nestmates and non-nestmates were conducted. These bioassays revealed that colony-specific cuticular hydrocarbon mimicry may function more to obtain prey from minor workers than to avoid eliciting aggression from nestmate major workers. These data also suggest that cuticular hydrocarbon proportions are used as colony recognition cues in ants. Myrmecophiles may obtain their mimetic cuticular hydrocarbons either directly from their host via direct contact or by biosynthesising them. Experiments reveal that C. bitaeniata avoids contact with workers, does not lose its mimetic hydrocarbons when isolated from workers, and does not biosynthesise its cuticular hydrocarbons. Additional experiments involving raising spiderlings on artificial diets reveal that the mimetic hydrocarbons of spiders are acquired by consuming the larvae of O. smaragdina. These data suggest that dietary acquired hydrocarbons can be transferred directly to the cuticle of spiders, via the haemolymph. Furthermore, the spiders have colony-specific hydrocarbon proportions if they eat the larvae from a single colony of O. smaragdina. The larvae of O. smaragdina also possess cuticular hydrocarbon proportions that are colony-specific. These data suggest that spiders chemically mimic the cuticular hydrocarbons of the larvae of their host.
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ItemThe dispersal distance of sessile benthic marine invertebrates, its predictors and consequences(University of Melbourne, 1998)This study focussed on an assemblage of sessile benthic marine invertebrates living on the pilings of a pier at Queenscliff in Port Phillip Bay, Victoria. I aimed to measure the dispersal distance of a suite of taxa from this assemblage, investigate the mechanisms behind any differential dispersal distance, look for simple predictors of dispersal distance and finally to determine whether differential dispersal was important for structuring populations and assemblages of these invertebrates. I measured the decline in recruitment density with distance from the pier (an isolated larval source) over a scale of approximately 40 m and in this way obtained a measure of realised dispersal distance for each of 27 taxonomic groups, including representatives of the sponges, bryozoans, ascidians and polychaetes. I found that for one group of taxa, recruitment was predicted to decline to 50% within 100 m of the pier (short-distance dispersers) while for another group of taxa there was no predicted decline to 50% within 1 km of the pier (long-distance dispersers). There were short and long dispersers within the sponges, bryozoans, ascidians and polychaetes so phyla did not predict dispersal distance. Developmental biology did appear to predict dispersal distance to some extent as the taxa with known planktonic spawning and external development had long distance dispersal. I investigated whether laboratory swimming time, swimming speed or other physical characteristics of larvae predicted dispersal distance but found that they did not. I measured the percentage abundance of each taxa that developed over a total period of 19 months at different distances from the pier (1 m to approx. 40 m). I used MDS and ANOSIM analyses to determine that distance from the pier resulted in significantly different assemblages, both at the recruit stage and the more mature stage of assemblage development. Thus, recruitment variation due to differential dispersal distance can result in significantly different assemblages developing at different distances from a source of larvae.