Browsing by Author "Truter, Johannes Christoff"
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- ItemAspects of the thermal ecology of the group-living lizard, Cordylus cataphractus : a spatial and temporal analysis(Stellenbosch : University of Stellenbosch, 2011-03) Truter, Johannes Christoff; Van Wyk, Johannes H.; Mouton, P. le Fras N.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Thermal ecology is a central theme in reptilian biology because of the thermodynamic rate dependence of virtually all biological processes in these ectothermic animals. Thermoregulation includes active processes (with associated energetic costs related to altered behaviour and physiology) functioning to maintain body temperatures within a preferred temperature range, so that the majority of physiological functions occurs optimally, despite natural variation in the animal’s thermal habitat. The recent development of quantitative thermal indices now allows researchers to describe the thermal habitat and thermoregulatory functioning of an ectotherm within its environment from a cost-benefit perspective. The use of such quantitative biophysical approaches to reptile thermal ecology studies is however limited in the African context. Cordylus cataphractus is one of the best studied cordylids, and exhibits various characteristics atypical for the family, such as permanent group-living, seasonally lowered surface activity, a low resting metabolic rate and large fat bodies. These characteristics are generally thought to be associated with groupliving in a semi-arid habitat, yet, the possible links to thermal ecology remains unexplored. The objectives of the current study was: firstly, to characterize the preferred temperature range (Tp) of C. cataphractus through the use of ecologically realistic laboratory thermal gradients; secondly, to explore seasonal and geographical variation in thermal preference, by comparing Tp among individuals captured from a coastal and inland population and during different seasons (autumn and spring); thirdly, to describe the thermal habitat of a C. cataphractus population during summer, autumn, winter and spring and to then relate these findings to the seasonal activity patterns reported in literature for the species; fourthly, to describe the seasonal patterns of thermoregulation (during summer, autumn, winter and spring) in a C. cataphractus population through quantitative thermoregulatory indices; fifthly, to assess geographic variation in the thermal habitat and IV associated patterns of thermoregulation in C. cataphractus among a coastal population (western range limit) and an inland population (eastern range limit). The thermal habitat of C. cataphractus was described by measuring operative environmental temperatures (Te) with hollow copper lizard models placed around rocks according to the natural surface movement patterns of the species. Variation in thermal habitat quality was subsequently calculated (de = |Te – Tp|) and averaged. Field body temperatures (Tb) of lizards were measured with dorsally attached miniature temperature loggers. Thermoregulatory indices were calculated from Te, Tb and Tp, describing: thermoregulatory accuracy, the effectiveness of thermoregulation and thermal exploitation for each population (coastal and inland) for the respective sampling periods. The preferred body temperature range of C. cataphractus is the lowest recorded among cordylids to date (mean Tp = 29.8oC) and was conserved among different populations and within these populations among seasons, despite the fact that environmental temperatures are known to vary geographically and seasonally. Thermal habitat quality varied significantly at micro spatial scale around rocks in the coastal population. Since C. cataphractus males are territorial, competition for thermal habitat quality around rocks may therefore occur. Such effects will be a function of the time of year since the variability in thermal habitat quality among rock aspects (around rocks) varied seasonally. Thermal habitat quality of crevices varied among seasons and was typically higher in the open, outside rock crevices, during the cooler winter and spring periods, whereas in summer and autumn the crevice environments were more favourable. Thermal habitat quality was high in crevices during autumn, suggesting that the observed repressed surface activity of C. cataphractus described for the time is not necessarily, as previously thought, only due to food constraints. Moreover, in contrast to earlier reports, the current results (Tb versus Te) indicate that individuals emerged from crevices in summer. The geographical assessment indicated that lizards from the coastal population, with generally larger groups, thermoregulated more successfully than those from the inland population. The higher thermoregulatory success in the coastal population occurred in spite of the fact that thermal habitat quality was significantly lower at the coastal locality. The higher thermoregulatory success in the coastal population was likely due to reduced predation risk associated with increased group-size. The seasonal trends in thermoregulation at the coastal and inland population corresponded to the patterns predicted by the cost-benefit model of thermoregulation, accuracy of thermoregulation and the effectiveness of thermal exploitation being higher during the thermally more favourable autumn.
- ItemTesting for endocrine disruptors in South African waters : a comparative study employing in vitro and in vivo screening approaches(Stellenbosch : Stellenbosch University, 2016-12) Truter, Johannes Christoff; Van Wyk, Johannes Hendrik; Oberholster, Johan Paul; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: Numerous natural and synthetic chemicals are known to interfere with the endocrine systems of wildlife and humans, i.e., endocrine disruptive chemicals (EDCs). Surface water bodies represent a major sink of EDCs and aquatic vertebrates including fish and amphibians are, therefore, at risk. Although research in the field of endocrine disruption has proliferated globally in the past two decades, only limited work describing the status of surface water has been performed in the South African context. The aims of this dissertation are: (1) to provide a detailed overview of the present literature on endocrine disruptive potential, i.e., EDC associated biological activity in South African surface waters; (2) address certain literature gaps by screening surface water, collected from different South African water bodies, using in vitro reporter gene assays (RGAs) and gene expression based biomarkers in Mozambique tilapia, Oreochromis mossambicus, exposed in vivo; (3) to compare the results of the in vitro hormone receptor RGAs and the in vivo gene expression based biomarkers to assess whether the risks predicted correspond; (4) evaluate the potential of O. mossambicus as environmental sentinel and source of biomarkers for potential disruption of the reproductive, thyroid and interrenal endocrine systems. The majority of research on endocrine disruption in South African surface waters has been focused on reproductive targets, whereas potential disruption of the thyroid, adrenal, pancreatic and other metabolism linked endocrine pathways are less well described. An inter-seasonal assessment of the Upper Olifants River (Mpumalanga) indicated alarmingly high concentrations of steroid estrogens and potent estrogenic activity in vitro in water collected from the close proximity of a waste water treatment plant (WWTP), indicating local fish may be adversely affected. Future studies evaluating the reproductive systems of wild captured fish inhabiting the Upper Olifants River will be of value. No association could be shown between altered endocrine signalling and the incidence of obesity and pansteatitis in the O. mossambicus population inhabiting Loskop Dam (Mpumalanga). Evidence of disrupted thyroid signalling was, however, observed in Loskop Dam fish relative to an alternative population. Gene expression biomarkers representing the reproductive, thyroid and interrenal systems in juvenile O. mossambicus suggest limited effects associated with exposure to surface water contaminated with neutralized acid mine drainage, containing high concentrations of Al, Mn, Ni, Co and Cu. In addition, evidence is given indicating the potential risk of crude oil contamination in fresh water to the reproductive and thyroid systems as well as lipid metabolism in wildlife. No significant changes in the expression of a selection of endocrine linked genes was, however, observed in Xenopus laevis tadpoles exposed for a short period to surface water collected from a freshwater pan into which crude oil contaminated water is periodically discharged. Further investigation, and in particular longer term exposures, as well as the evaluation of aquatic fauna collected from (environmental) fresh water bodies contaminated with crude oil are required. Surface water collected from river mouths and harbours in the eThekwini Metropolitan and City of Cape Town was shown to exhibit estrogenic and anti-androgenic activity in vitro, suggesting the reproduction of fish populations may be impaired. Future studies evaluating the endocrine systems of wild-captured fish from the aforementioned coastal systems are needed. The risks associated with exposure to surface water predicted by in vitro RGAs did not in all cases correspond to the potential biological activity indicated by in vivo gene expression based biomarkers. This study, therefore, provides evidence supporting the use of a combination of in vitro and in vivo techniques to evaluate surface water for endocrine disruptive activity/risk. Juvenile O. mossambicus exposed for a short period was not sensitive to estrogenic substances, but biomarkers relating to thyroid disruption are more promising.