4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Morphological changes in the lungs and air sacs of the Japanese quail (Coturnix japonica) exposed to heat stress(University of the Witwatersrand, Johannesburg, 2023-08) Abdulkadir, Abdurrahman; Reddy, DeranThe Japanese quail presents a potential protein food security alternative in rural sub-Saharan Africa because of its small size and easy husbandry. The nutritional and therapeutic value of its meat and egg makes it an interesting and better choice than chicken in some parts of the world. In addition, researchers used Japanese quail as an animal model of human genetic and developmental disorders because of its short generational interval. However, global warming threatens its welfare by propagating heat stress. The physiological response of Japanese quail under heat stress causes negative performance and sometimes instant mortality. Hence, in this study, lung of the quail under heat stress was microscopically examined as it is the most important organ for survival under heat stress. All other organs depend on the lungs for oxygen, and it is also the most crucial in evaporative cooling. A total of 38 Japanese quail were used in this study. A pilot study was conducted that used eight quails, to ensure the possibility of survival under the proposed experimental temperatures. Afterwards, 30 quails were randomly allocated — based on initial body mass— to five groups of six quails each. The control groups (CT and CT2) were maintained at a thermoneutral temperature of 25°C throughout the experiment while acute heat stress group (AH) were maintained at 38°C for 24 hours only. The chronic heat stress groups (CH1 and CH2) were maintained at 35°C for seven days and 28 days respectively. Body mass, cloacal temperature, and respiratory rate of quails were measured daily to monitor health and detect any serious ill health from heat exposure. Food and water were provided ad libitum. At the end of the experiment, all quails were terminated using an overdose of anaesthetic and lungs were harvested and processed for microscopy. Lung weight, volume and size were measured before sampling. Tissue samples were processed, and sections were cut with a microtome and stained with Mayers H&E, new pentachrome stain and Gomori’s one-step trichrome stain. Other tissue samples were triple immunolabelled with anti-α-SMA and Collagen 1 antibody and DAPI nuclear stain. Tissue samples were also processed for scanning and transmission electron microscopy. No significant difference in body mass, cloacal temperature, respiratory rate and lung parameters was found in heat-stressed quails compared with control. However, microscopic examination revealed blood congestion and excessive leakage of blood into airway of lungs in heat-stressed groups compared with the control. In addition, there was structural damage to parenchyma and blood vessels, which incites an inflammatory response causing deposition of collagen fibres in some areas of the lungs in heat-stressed groups. Interestingly, these effects occur in a time-dependent pattern. The most impact is seen in AH and CH1 groups while CH2 shows signs of recovery. In conclusion, Japanese quail lung was negatively impacted by heat stress, which can lead to instant mortality or long-term reduction of performance. Despite the evidence from this study suggesting that Japanese quail can adapt to the effects of heat stress if it survives the initial impact, a conscious effort must be made to alleviate or remove heat stress for quality outcomes.Item A documentation of the morphology of the lungs of the Sprague Dawley rat after chronic heat exposure(University of the Witwatersrand, Johannesburg, 2023) Peya, Yolanda; Reddy, DeranClimate change is a natural phenomenon that is exacerbated by mul4ple human ac4vi4es in the environment. These ac4vi4es lead to a rise in global temperatures. This increases the occurrence of heatwaves which pose a major threat to ecosystems, biodiversity, and the conserva4on of species on Earth. This study, aimed to document the effects of chronic heat exposure on the lungs of the Sprague Dawley rat using histological and immunofluorescence techniques. Twenty-four (24) rats were assigned to three groups; each exposed to different temperatures; (i) group A (n = 8) exposed to 25 °C (ii) group B (n = 8) exposed to 33 °C and (iii) group C (n = 8) exposed to 34 °C. This was done for a period of 4 weeks and the rats were euthanised therea`er. Methods employed included Intratracheal instillation, and histological and immunofluorescence techniques. This study found that rats in group A (25 °C) displayed no structural adapta4ons in comparison to groups B and C. Enlarged blood vessels with thick smooth muscle and prominent elas4c fibres, bronchus-associated lymphoid 4ssue (BALT), and increased collagen deposi4on were observed in group B (33 °C). These indicate the ac4va4on of immune responses and adapta4on to new environmental temperatures. In group C (34 °C), the lung morphology was severely damaged. There was an increased loss of epithelial integrity, oedema, pulmonary alveolar proteinosis (PAP), and a severe decrease in the lung- to-surface area ra4o. The significant changes caused by the 1 °C temperature difference between groups B (33 °C) and C (34 °C) illustrate the detrimental effects of chronic heat stress. It is evident that increasing environmental temperatures due to climate change is harmful to life and immediate interven4ons are necessary to combat rising temperaturesItem South African Podocarpaceae distribution interpreted from a physiological and population genetics perspective(University of the Witwatersrand, Johannesburg, 2023-09) Twala, Thando Caroline; Fisher, Jolene T.; Glennon, Kelsey L.Podocarpaceae (podocarp) are the most diverse conifer family with a Southern Hemisphere distribution. Podocarps occur in Afrotemperate and Afromontane forests at high elevations that are cool and humid. Podocarps once dominated the forest canopy but due to their slower growth rate and photosynthetic rates they have are in competition withangiosperms which have faster growing and higher photosynthetic rate. Due to the competition between podocarps and angiosperms, Bond (1989) proposed that podocarps were excluded to nutrient poor and unfavourable environments due to their limited competitive ability. However, podocarps persist under the forest canopy until conditions become favourable. This power dynamic shifts with climate oscillations where podocarps distributions expand and dominate when conditions become cooler. Owing to podocarps being the most diverse and widespread conifers they make for a good study system. This thesis focuses on understanding the climatic variables driving the current and future distribution of podocarps, how their seedling physiology may influence their ability to recruit and establish under climate change, and how this can influence their ability to disperse in their South African distribution. Ensemble species distribution modelling was used to characterise the current and future distribution of podocarps and identify the climatic variables that influence their distribution. The current and future environmental niche was quantified using environmental niche modelling. I found that variables predicting rainfall seasonality were the most important at determining the distribution of podocarps in South Africa. Afrocarpus falcatus and P. latifolius were predicted to have the largest geographic distribution, with P. henkelii and P. elongatus having restricted distributions. Both A. falcatus and P. latifolius were predicted to occur in the Limpopo, Mpumalanga, KwaZulu-Natal, Eastern Cape and Western Cape provinces of South Africa. Podocarpus henkelii was predicted to occur in the KwaZulu-Natal and Eastern Cape provinces. Podocarpus elongatus is endemic to the Western Cape Province. All four podocarps were predicted to expand to higher altitudes (up the escarpment) under climate change and contract in its coastal distribution. Although P. elongatus was predicted to occupy the smallest geographic distribution it was predicted to have the widest environmental niche than the other species, which was predicted to contract under climate change. The environmental niche of P. latifolius and P. henkelii was predicted to remain stable. Afrocarpus falcatus, P. latifolius, and P. henkelii showed niche conservatism, however, P. elongatus under RCP 4.5 → current and the RCP 8.5↔ current niche comparisons showed niche divergence. Podocarpus elongatus was predicted to expand to an environment it currently does not occupy. Ecophysiological and morphological experiments were conducted to understand how podocarp seedlings respond to drought and elevated temperatures. The experiments indicated that P. henkelii seedlings were more drought and heat tolerant than A. falcatus seedlings. Conditions are predicted to become hotter and drier in some parts of South Africa, and this study has shown that P. henkelii seedlings will be able to tolerate these conditions better than A. falcatus seedlings. Furthermore, this suggests that the distribution of P. henkelii is not constrained by its physiology but rather by other mechanisms such as competition, reproductive biology, and/or shade tolerance. Microsatellites were used to inform us about possible podocarp dispersal patterns in A. falcatus, P. latifolius and P. henkelii in South Africa. The results suggested that podocarp populations in South Africa were shown to have higher genetic diversity than other podocarps globally, however these results may be due to the limited number of microsatellites used in this study, smaller population sizes in comparison to other studies and methods used to measure population structure and diversity. As expected, the geographically widespread species (A. falcatus and P. latifolius) are more diverse than the geographically restricted P. henkelii. Geographically distant A. falcatus and P. henkelii populations showed higher differentiation than geographically proximal populations. In P. latifolius South African populations, there was strong isolation by distance. Although the distribution of podocarps is disjunct, there is dispersal between populations. Podocarps are resilient to climate change as was demonstrated by the work in this thesis, and by their paleodistribution expanding and contracting with climate oscillations. In this thesis I considered climate, ecophysiology and genetics as determinants of podocarps distribution. Under climate change, podocarps are predicted to expand to higher elevations to track favourable climatic conditions. Seasonal drought is the most important climatic determinant of podocarp distribution. The ability of these species to tolerate drought and heat stress suggests that the seedlings might be able to tolerate short periods of drought and heat stress, however prolonged exposure may lead to seedling mortality, but populations will then be maintained by adults. Populations show evidence of gene flow, indicating they will be able to persist through changing climates, as they have done in the past. This thesis has highlighted that the factors constraining podocarp distributions might be demographic, and future works should investigate the role of fire in podocarp seedling establishment and longevity, as well as their interactions with angiosperm competitors.