Faculty of Science (ETDs)

Permanent URI for this communityhttps://hdl.handle.net/10539/37933

For queries relating to content and technical issues, please contact IR specialists via this email address : openscholarship.library@wits.ac.za, Tel: 011 717 4652 or 011 717 1954

Browse

Filters

20242

Settings

Subject: search.filters.subject.Activity

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Behavioural and physiological responses of sable antelope to heat and aridity
    (University of the Witwatersrand, Johannesburg, 2024-10) Haylock, Kiara Avelyen; Hetem, Robyn; Parrini, Francesca
    The increased probability of longer, more extreme dry seasons, due to rapidly rising temperatures and the increased frequency and intensity of droughts, threatens water-dependent, selective grazers throughout Africa. Phenotypic plasticity such as behavioural adjustments and physiological flexibility may buffer the impacts of spatiotemporal variations in resource availability and climate. My project aimed to assess variations in home range size, movement distances, behavioural states of movement, fine-scale activity, microclimate selection and body temperature of sable antelope (Hippotragus niger niger), a water-dependent selective grazer, in relation to spatiotemporal variation in vegetation greenness and environmental heat load. To address the aim of my project, I measured body temperature and fine-scale activity using biologging in ten free-living GPS-collared sable antelopes in the semi-arid Bwabwata National Park of Namibia. Each collar was fitted with a miniature black globe thermometer to assess microclimate selection. A weather station with a standard black globe thermometer recorded black globe temperature and air temperature. Data collection spanned 24 months, from May 2016 to April 2018. The dry season was a critical period for sable antelopes, particularly the late dry season when high ambient temperatures compounded reduced resource availability. As conditions became hotter and browner with the progression of the dry season, home ranges elongated towards the Kavango River and increased in size by ~50% from the early dry to the late dry season. In response to increased 24-hour mean black globe temperature and increased exposure to brown vegetation, the 24-hour mean hourly displacement distance of sable antelopes increased with progression of the dry season, mostly due to the increased frequency of long, directed movements to the Kavango River during the late dry season. One sable antelope travelled between 13 and 30 kms every 4-5 days to access water from the river during the late dry season. Using Hidden Markov Models, four behavioural states were identified from the movement tracks of sable antelopes: resting, foraging, local movement and relocating. The long, directed movements to water, classified as a relocating behavioural state, predominated during the late dry season. Sable antelope displayed an increase in relocating behaviour and a decrease in foraging behaviour associated with high 24-hour mean black globe temperature and increased proportion of brown vegetation exposure. Sable antelopes also displayed an increase in local movement with increased exposure to brown vegetation and high 24-hour mean black globe temperature, but a decrease in resting behaviour with an increase in the proportion of brown vegetation exposure. Driven by decreasing vegetation greenness and increasing black globe temperatures, sable antelopes reduced their diurnal proportion of activity with progression of the dry season, associated with a reduction in activity during the heat of the day in response to increased exposure to brown vegetation, high 24-hour mean black globe temperature and an increased proportion of time spent in the shade. Sable antelopes did not fully compensate for lost diurnal activity, despite increased nocturnal activity during hot and dry conditions, as total 24-hour activity decreased with progression of the dry season. Sable antelopes also selected higher quality microclimates (i.e. microclimates that were on average 6.7 ± 0.2 oC cooler than direct sun) when increasingly exposed to brown vegetation and high 24-hour maximum black globe temperature. Fluctuations in 24-hour body temperature increased during the dry season with maximum amplitudes of body temperature rhythm of >5 oC within a single day during the late dry season. Sable antelopes displayed a reduction in minimum 24-hour body temperature in response to decreased 24-hour black globe temperature and increased exposure to brown vegetation during the early dry season, likely due to energy deprivation. While minimum body temperatures remained low during the late dry season, sable antelopes displayed an increase in maximum 24-hour body temperature in response to increased mean 24-hour black globe temperature and increased exposure to brown vegetation, likely due to water deprivation. High maximum 24-hour body temperatures, indicative of dehydration-induced hyperthermia, increased the likelihood of relocating movements to the Kavango River which in turn were associated with a subsequent decline in maximum 24-hour body temperatures. By linking body temperature to a behavioural state of movement, I am the first to demonstrate a direct link between access to a water resource and maximum body temperature in a free-living antelope species. The behavioural flexibility exhibited by sable antelopes during the dry season failed to buffer reduced resource availability as fluctuations in body temperature indicated that sable antelopes experienced nutritional and water stress. My findings highlight the importance of incorporating physiological measurements into behavioural and ecological studies to inform management decisions and improve conservation efforts in the face of climate change.
  • Thumbnail Image
    Item
    Biophysical evaluation of the kinetics, thermodynamics, and structure-stability relationship of Wuchereria bancrofti glutathione transferase in comparison with human µ and π glutathione transferases
    (University of the Witwatersrand, Johannesburg, 2024-06) Oyiogu, Blessing Oluebube; Achilonu, Ikechukwu Anthony
    Lymphatic filariasis is an endemic disease caused mainly by the Wuchereria bancrofti parasite and has been classified as a major neglected tropical disease. The emergence of drug-resistant strains of W. bancrofti and the limited efficacy of the available drugs on adult worms threatens the eradication of the disease. W. bancrofti glutathione S-transferase (WbGST) is a homodimeric enzyme central to detoxifying electrophilic compounds in the parasite due to its lack of cytochrome P-450. Therefore, WbGST is a potential therapeutic target for lymphatic filariasis. Bromosulphophthalein (BSP) and epigallocatechin gallate (EGCG) were previously shown to inhibit glutathione S-transferase activity. In this study, the interaction of WbGST with BSP and EGCG in comparison with human glutathione S-transferase P1-1 (hGSTP1-1) and human glutathione S-transferase M1-1 (hGSTM1-1) isoforms was investigated. Soluble WbGST, hGSTP1-1 and hGSTM1-1 were recombinantly produced and purified successfully to homogeneity. Glutathione and 1-chloro-2,4-dinitrobenzene conjugation assay was employed to analyse the enzyme activity, kinetics and inhibitory potency of the compounds. Spectroscopic studies were employed to investigate the functional and structural impact of ligand binding to the enzymes. Both thermal and chemical stability studies were performed, and binding energetics were analysed using isothermal titration calorimetry. The activity of WbGST was predominantly inhibited, with IC50 values of 5 μM for BSP and 12 μM for EGCG. The EGCG displayed uncompetitive and mixed modes of inhibition towards WbGST with respect to glutathione and hydrophobic binding sites, respectively. Whereas BSP showed a mixed type of inhibition for both active sites of WbGST. Ligands reduced the turnover rates (kcat) and the catalytic efficiencies (kcat/KM) of the enzymes. Upon ligand binding, 8-anilino-1-napthalene sulphonate was displaced from WbGST and hGSTM1-1 by 67%(BSP), 24%(EGCG) and 72%(BSP), 5%(EGCG), respectively; suggesting that the ligands bind to the 8-anilino-1-napthalene sulphonate binding site. Stability studies indicate that WbGST is the least stable of the three enzymes and that glutathione increases its stability. Isothermal titration calorimetry showed that BSP binds to multiple sites in WbGST with binding at site-1 (S1) and site-2 (S2), which are entropically and enthalpically driven, respectively. S1 showed a higher affinity for BSP than S2. EGCG binding to WbGST was entropically driven. BSP had a higher affinity for the enzymes than EGCG. All the results indicated that the ligands significantly impact WbGST more than the human GSTs. Further investigations, such as crystallography and molecular dynamics simulations, will shed more light on the ligan-protein interactions on a molecular level. Overall, this study suggests that BSP and EGCG are efficient inhibitors of WbGST that probably bind to both L and H-sites of WbGST, altering catalytic activity of the enzyme. The unique properties of the L-site are particularly suitable for rational drug design. Therefore, both ligands can be repurposed as new-generation therapeutics against filariasis.