School of BioSciences - Theses
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ItemThe effect of cardiovascular diseases on resistance vasculature and the efficacy of different treatments( 2019)Diabetes and hypertension are conditions that contribute to cardiovascular disease, which is a major cause of morbidity and mortality in the developed world. As the prevalence of obesity rises, the health burden will only increase. Vascular dysfunction, characterised by endothelial dysfunction and increased arterial stiffness, is a hallmark of cardiovascular disease and a major risk factor for the development of further cardiovascular events. Animal models are a necessary tool for diabetes research to elucidate disease pathologies and investigate potential treatment options. However, the precise disease pathology in different animal models of diabetes remains unknown. Further characterisation of vascular dysfunction in cardiovascular disease will help determine treatment options. Annexin-A1, an anti-inflammatory molecule that acts as a second messenger of the glucocorticoid pathway, has beneficial effects in diseases like diabetes, ischaemia-reperfusion injury and stroke. However, its effects on the vasculature remain unknown. The peptide hormone relaxin has shown some promise as a vasoprotective agent. My thesis first aimed to increase understanding of the pathogenesis of vascular disease in different animal models of diabetes. I then investigated the effects of annexin-A1 deficiency on the vasculature to determine the potential therapeutic role of annexin-A1. Finally, I explored the efficacy of relaxin treatment in a hypertensive model of vascular dysfunction. In Chapter 3, I describe the mesenteric vascular phenotype in moderate hyperglycaemia (20mM blood glucose) compared to severe hyperglycaemia (< 30mM blood glucose). While both models showed increased arterial stiffness, only severe hyperglycaemia caused endothelial dysfunction, indicating that arterial wall mechanics are more sensitive than endothelial function to increased blood glucose. Chapter 4 further investigated the effects of type 2 diabetes on the mesenteric vasculature. This study utilised a high fat diet with low dose STZ in mice to induce insulin resistance. Furthermore, this study characterised the effects of annexin-A1 deficiency on arterial remodelling in both insulin resistance and insulin deficiency. The main findings were that insulin resistance induced significant outward remodelling but had no effect on passive stiffness. Interestingly, insulin resistant annexin-A1 gene knockout mice had significantly increased vascular stiffness. Insulin deficiency induced outward remodelling and increased volume compliance in the mesenteric artery, regardless of genotype. Relaxin treatment reverses endothelial dysfunction in the mesenteric artery in hypertension and diabetes over a short treatment duration (<72 hours). However, the effect of a longer treatment duration in hypertension has not been investigated. Chapter 5 demonstrated that 10 days of continuous relaxin treatment reversed mesenteric artery endothelial dysfunction in hypertension by augmenting NO and EDH-mediated relaxation. Overall, my thesis further characterised the vascular phenotype in animal models of type 2 diabetes, which is important in understanding the disease process and for testing potential treatments. Additionally, I showed that both annexin-A1 and relaxin have the potential to be used as successful treatments in vascular dysfunction in the setting of diabetes and hypertension.
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ItemThe physiological effects of artificial light at night on the Australian black field cricket( 2018)The presence of artificial light at night (ALAN) is one of the fastest growing, most pervasive and, until recently, under-appreciated forms of global pollution. Current ALAN levels in urban environments are associated with changes to animal behaviour, dramatic shifts in the timing of life history events, reductions in individual fitness and disrupted physiological processes, including immune function. This thesis explores the physiological effects of ecologically relevant levels of ALAN on a model invertebrate species, the Australian black field cricket, Teleogryllus commodus. In Chapter 1, I reviewed the literature with a particular emphasis on the physiological effects of ALAN, including growth, survival, reproductive success, and immune function. I also speculate as to the potential mechanistic links behind these ALAN induced biological effects. In Chapter 2, I explored experimentally the effects of ecologically relevant levels of ALAN (1, 10 and 100 lux) on life history and fitness traits of the black field cricket. Under controlled laboratory conditions, I reared crickets from egg to adult in an environment with either no ALAN (0 lux) or one of the above dim-ALAN intensities and assessed the consequences of ALAN for growth, survival and reproductive success. I demonstrated that egg hatch, adult survival and reproductive measures were largely unaffected by the presence of ALAN, however juvenile development time was longer and adults were larger when crickets were exposed to any light at night (1, 10 or 100 lux). In Chapter 3, I examined the effects of ALAN (1, 10 and 100 lux) on three key measures of adult immune function (haemocyte concentration, lytic activity, and phenoloxidase activity). The presence of any ALAN (1, 10 or 100 lux) had a clear negative effect on the cellular immune response. Specifically, individuals exposed to any ALAN were unable to increase their haemocyte concentration in response to a stressor challenge. In Chapter 4, I investigated a novel method for the measurement of circulating melatonin in small samples of cricket haemolymph using high-performance liquid chromatography tandem mass spectrometry, with methyl tert-butyl ether (MTBE)/ethyl acetate as an extraction agent. The calibration curve for melatonin was linear in the range of 0.25 and 10 pM (R2 = 0.999), and the limit of detection was 0.25pM. When applied to a set of pilot data from crickets reared under different ALAN environments (0, 1, 10, and 100 lux), the results were however inconclusive, due to small sample sizes. In Chapter 5, I discuss the significance of these findings and their ecological implications. My thesis advances our understanding of the biological ef fects of ALAN for invertebrates, a key taxon contributing to ecological community structure and composition. It is one of the first set of studies to simultaneously investigate multiple traits in the same individuals exposed to lifelong ALAN, and to assess changes in immune function throughout their adult life. Combined, the results presented demonstrate a disruption to physiological processes, and highlight the potential for ALAN to alter the phenology of communities and reduce the overall fitness of individuals.
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ItemEvaluating uncertainty when applying the trait-based protocol for climate-change vulnerability in freshwater crayfish( 2018)Climate change has been recognized as one of the greatest threats to the persistence of biodiversity. Several approaches have been used to assess species’ vulnerability to climate change such as correlative niche models, mechanistic models, trait-based models, and combination of these model outputs. The trait-based protocol for climate-change vulnerability assessment (TVA) is increasingly used in a variety of taxa due to its suitability for assessing data-poor species. Yet, TVA has thus far remained unevaluated for potential uncertainties. In TVA, climate change-relevant traits are selected and scored against three dimensions: sensitivity, adaptive capacity, and exposure to climate change. In this thesis, I applied TVA to assess climate-change vulnerability in a data-poor invertebrate taxon (freshwater crayfish; 574 species) and explored the potential sources of uncertainty in TVA. I found that climate-change vulnerable crayfish are distributed globally with high concentrations in the USA and Australia, reflecting global pattern of crayfish richness. Ninety-one species are already identified as vulnerable to climate change in the IUCN Red List. I identified hotspots of species vulnerable to climate change that require additional conservation action. I assessed multiple sources of uncertainty including trait selection, the use of arbitrary thresholds for quantitative traits, and climate model choices. I quantified that in TVA, it is likely that as more trait variables are included in the study, more species are identified as vulnerable to climate change. The use of arbitrary thresholds in TVA was relatively robust to produce species’ vulnerability ranking. However, I found that the number of species identified as vulnerable to climate change varied greatly (79-156) depending on which individual climate model was used. TVAs are an effective tool to understand climate change vulnerabilities of data-poor species, however, assessors applying the protocol should be aware of these uncertainty sources and perform sensitivity analyses to better understand their impact on TVA results.
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ItemCharacterisation of seed germination in sea rockets (Cakile spp.)( 2017)The sea rocket genus (Cakile) includes several species; two of these are C. edentula and C. maritima. Both are invasive and have become widely distributed throughout the world. C. edentula was introduced earlier than C. maritima in Australia, and quickly expanded. However, after C. maritima was introduced to Australia, C. edentula disappeared from many regions. This replacement of C. edentula by C. maritima has occurred in other areas of the world. An exception also exists where the two species show coexistence in climates where the winters are cold and summers are wet. Several hypotheses have been raised to explain this replacement. In this thesis, a difference in the germination timing of the two species was hypothesised to be of importance in different climates. In order to work towards understanding and predicting germination of Cakile species, the germination of C. edentula from two different climates was examined in this thesis. A hydrothermal time model was used to describe seed germination. The results showed that populations from different climates differ in seed germination behaviour. The C. edentula population from temperate area showed lower base temperature and smaller hydrothermal time accumulation requirement than that from sub-tropical area. Overall, the sub-tropical population germinated more readily than the temperate population across almost all experimental conditions. Dormancy was found in C. edentula seeds during the germination experiment. Further study therefore investigated methods in relieving dormancy of the two Cakile seeds to see whether they responded differently. Two treatments (i.e. damage on seed coat and cold stratification) were applied. The results indicate that C. edentula generally had a higher percentage germination than its counterpart in each treatment (including the control group) while C. maritima germinated faster than C. edentula under most damage levels. The data generated by this thesis could be used as the basis of comparing germination timing between the two Cakile species. For predicting the germination timing more effectively, populations of both species from more climates are required, and dormancy needs to be studied under field conditions.
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ItemSources of variation for heat resistance in Drosophila hydei: developmental rearing and hardening acclimation, cross generational effects, (sex) and laboratory adaptation( 2016)Temperature is often seen as being the most important intrinsic variable which shapes how successfully an ectotherm persists in its environment. How ectotherms respond to increases in temperature, a likely occurrence given current climate change trends, will therefore often shape their future survival and distribution patterns. Drosophila is a widely used model to study adaptation to changing thermal conditions, with studies focussing on both genetic and non-genetic factors associated with adaptation. Plastic effects on thermal resistance have been studied in Drosophila with short term (thermal shock hardening) and long term (acclimation) exposure to temperature eliciting non-genetic responses. The evolution of these plastic effects are not currently well understood, but the field remains important in determining short term responses in nature. Selection experiments measuring the underlying genetic potential of populations to modulate their upper and lower thermal limits have been carried out on several species, with both the thermal assay used as well as the environmental conditions being used for testing considered important in dictating the selection response. In this thesis, the main theme which permeates throughout involves the sources of variation which influence heat resistance in Drosophila hydei. In the second Chapter of this thesis, the presence of cross generational effects was investigated for heat resistance in D. hydei. A thermal rearing regime was developed to investigate whether these short term effects were detectable at different stages of introduction in the laboratory environment and for how long they persist. Weak evidence for cross generational effects were detected in populations newly introduced into the laboratory, however these effects were not consistent in direction. When populations were re-tested, no evidence for cross generational effects was found. As a by-product of the re-testing process, a uniform increase for both populations and experimental condition was detected for increased heat resistance. The possibility for laboratory adaptation was posed and laid the groundwork for the third Chapter of this thesis. To investigate potential laboratory adaptation, an experimental protocol involving multiple populations of D. hydei with different times spent in the laboratory but tested for their heat resistance at the same time was used. As well as using two developmental rearing temperatures, the effects of sex, and of heat hardening were incorporated into the experiment. Two experimental timepoints were used with six months separating them. Most populations were re-tested at the second timepoint which allowed direct comparison for the evolution of those populations. Evidence for laboratory adaptation was found, with the oldest population displaying significantly lower levels of heat resistance compared to all other populations. Unusually high heat resistance levels were recorded for populations newly introduced into the laboratory, while populations showed an increase in resistance between the two experimental timepoints. The effects of developmental rearing temperature were substantial, and were matched only by population differences. The influence of hardening was non-significant as a standalone variable, but it did interact significantly with the sex of an individual. This thesis has added knowledge to the field of thermal biology and has supplemented other studies showing the ability of Drosophila to modulate its thermal resistance in response to differing environmental variables. The effects of laboratory adaptation on heat resistance have rarely been considered in the literature, and this study, whilst not definitive, suggests the importance of this factor in adaptation.
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ItemManagement structures of Tiwi indigenous landowners and responses to changing resource values( 2015)The Tiwi people of northern Australia have managed their land and natural resources continuously for 6000–8000 years. The elegance of traditional governance structures and decision making strategies discussed in this thesis illustrates how they did it; how reliable harvests were sustained, and how land and resources were maintained through generations. This study also includes more recent [from 1960] contrasts of post traditional land use highlighting impacts and responses of managers and landowners through their continuing transition from traditional to a market economy. Impacts and responses of this kind readily accord with a focus on social ecological systems and their management which frame the theoretical approach undertaken in this thesis. The reasons for this emerge from the prominence and persistence of Tiwi decision making techniques that influence land management actions and responses. Managers gathering information for their decisions rely upon embedded elements now vulnerable to changing meanings and beliefs. For example, traditional aspirations were attainable through knowledge and monitoring of landscape systems, and access sanctions that assured sustainable harvests. These elements are no longer available to post traditional decision makers. Landowner participation is no longer required to access or harvest resources; and the value of those resources, once a community consumption satisfaction, has been monetised. Achieving aspiration levels continues; the meanings have changed. Governance structures that once supported traditional processes with sanctions and verifications preserving their influence need also adapt to different meanings and beliefs. Impacts shaping social-ecological systems also shape the minds of those people managing them. None more so than monetised resources and rational economics. As task environments change they provide contrasts accentuating responsive Tiwi principles of adaptive management. Impacts can be identified through indicators revealed by these contrasts. Modifying the effects of impacts requires decisions for the use and management of developed land focus on the resilience of landscapes; be open to scientific collaboration to achieve it, and set within transparent and legitimate own governance structures. We provide a framework of indicators to reference Tiwi responses in these categories. Each category is touched by aspirations of land owners and managers asserting their own controls through Tiwi decision strategies. They are strategies that exploit the structure and attributes of the environment within which decision(s) are made. Aspirations change when a changed environment alters the categories of benefits sought from land resources. Decision strategies are then open to attributes of a new environment accommodating values of rational economics. Where aspirations once satisfied immediate resource needs they contained attributes capable of delivering long term sustainable resource management. Tiwi aspirations can no longer be relied upon to achieve those outcomes. By evaluating the relationship between changing land use and aspirations to benefit from that use, adaptive management systems can be observed evolving as aspirations change. Indicators are able to capture the changes occurring. They illuminate impacts occurring to Tiwi governance structures and to the principles that governance has relied on. Primarily, traditional governance established aspiration pathways and provided guidance for their attainment. Short cuts to attainment were strictly contained. This significant doctrine enshrining aspiration management techniques remain within traditional memory of the current generation. The capacity of adaptive governance to manage new aspirations by way of revised sanctions and achievement pathways suggests some prescriptions are possible for effective environmental management and conservation of Tiwi land in the longer term.
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ItemPhytoextraction of cadmium by species of the Brassicaceae( 2015)This thesis contributes to the knowledge of metal-tolerant and metal-accumulating plant species for use in the field of phytoremediation. A broader range of species of Brassicaceae has been assessed for cadmium tolerance and uptake than has previously been tested. Cadmium (Cd) was chosen as the target metal for phytoremediation due to its high toxicity at low contaminating concentrations. The Brassicaceae family is an important potential source of species for phytoremediation as it is host to the largest number of metal hyperaccumulating species and also includes metal-tolerant species capable of accumulating various metals, including Cd. The capability of untested members of the family Brassicaceae to accumulate and tolerate Cd, the effect of Cd exposure and concentration on shoot nutrient homeostasis and the effect of Cd exposure and concentration on the expression of metal transporter HMA4 was investigated in hydroponic experiments. The feasibility of candidate species to phytoextract Cd from contaminated soils and biosolids was assessed in both glasshouse and field conditions. In addition, the localisation of Cd in aerial tissue was investigated. Of 19 previously untested species encompassing four genera of the Brassicaceae, five species, B. oleracea gongylodes (kohl rabi), B. oleracea capitata (cabbage, variety Golden Acre), B. oleracea (collards), B. oleracea acephala (kale, Half Scotch Tall) and Erysimum scoparium (wall flower), were identified as Cd tolerant from hydroponic studies. The concentration of Cd in the aerial tissue in the species tested varied from 60 to 370 µg Cd g–1 DW. Cadmium tolerance was not correlated with aerial Cd concentration (µg g-1 DW), however, total aerial Cd (µg plant–1 DW) was proportional to total aerial biomass (mg plant–1 DW) (r=0.92), demonstrating the importance of biomass in the phytoextraction of Cd. Exposure to Cd resulted in decreased Fe and Zn concentrations and increased Ca, Na and Mg concentrations in aerial tissues. Orthologues of HMA4, a gene encoding a metal transport protein capable of root-to-shoot transport of Cd, were detected in kohl rabi, pak choi, collards, wild mustard, senposai, kale, turnip and radish. Putative paralogues were observed in half of these species. The presence of identical sequences in Brassica species originating from different genomic backgrounds as well as more distantly related species of Brassicaceae, suggests an ancestral duplication event of HMA4 occurred before the evolution of these species. An expression analysis using reverse-transcriptase PCR of turnip, senposai, kohl rabi and kale detected HMA4 in the root tissue only, with no expression detected in kale. When plants were exposed to increasing Cd concentrations, HMA4 expression increased in both turnip and senposai, corresponding to medium to high levels of Cd accumulation respectively. Expression of this gene did not change in kohl rabi, which is consistent with low levels of Cd accumulation in this species. This finding supports the role of HMA4 in root to shoot transport of Cd. In the glasshouse pot trial, the candidate species (radish, tsoi sim, kale and senposai) demonstrated the capability to grow in biosolids provided as 100% substrate and survived in soil and biosolids contaminated with 8 µg Cd g-1 and 25 µg Cd g-1, respectively. In contrast to the high values observed in the hydroponics trial, the Cd concentrations in the aerial tissues of the candidate species ranged from 2 to 8 μg g-1 when grown in contaminated soil, and from 15 to 40 μg g-1 when grown in contaminated biosolids. There was no measurable reduction of Cd content in the contaminated soil or biosolids in which the plants had been grown. Biomass production of plants grown in contaminated biosolids was more substantial in the field trial. This was reflected in the greater amount of Cd extracted per plant than in the glasshouse pot trial, despite lower aerial tissue concentrations (5 to 9 µg g-1 DW). Kale and senposai extracted 100 and 50 µg Cd per plant respectively, however, this is too low to be economically viable. The attempt to identify the major sequestration sites within the aerial tissue of senposai and radish plants grown in the biosolids field using micro- Proton-Induced X-ray Emission/ Energy-Dispersive X-ray (PIXE/EDX) was not successful. The localisation of Cd in aerial tissue of these species remains elusive. Naturally occurring, high biomass, Cd accumulating plant species suitable for the phytoextraction of Cd from contaminated substrates are yet to be identified. Two major approaches to develop phytoextraction technologies are through breeding and transgenics. Of all the species examined, kale and senposai have the greatest potential for the phytoextraction of Cd. They tolerate and accumulate Cd, produce an extensive multi-branched root mass, are fast growing and easily harvested and they extracted more Cd per plant than the other species tested. Kale and senposai should be considered as suitable candidates for improving phytoextraction through genetic transformation with key hyperaccumulating genes such as MTP1 and HMA3 & -4.