School of BioSciences - Theses
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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.