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.