published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

No description available.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Molecular Biology / Master / Master of Philosophy

published_or_final_version / Molecular Biology / Master / Master of Philosophy

Direct and correlated responses to selection for weight gain were investigated after nine generations of within family selection. Four selection criteria were used: gain between 28 and 38 or 48 and 58 days of age, and under two feeding regimes, ad libitum consumption or restricted to 80% of control lines. Two lines consisting each of twenty pair matings were selected under each of these criteria. Two unselected control lines were kept. Carcass composition analyses were performed in generation nine at the beginning and end of each selection period and at 100 days of age. / Direct responses to selection in the first period were greater in the ad libitum lines while in the second period direct responses were greater in the restricted lines. Direct responses and realized heritability estimates were significantly different between the sexes; males had greater direct responses and higher heritabilities in all selected lines. Body weights before the selection periods decreased in all lines as a result of selection. Body weights after the selection period were not different from controls in the ad libitum lines while restricted lines remained smaller animals. Correlated responses in feed efficiency and feed consumption in the ad libitum lines were positive in the first period and negative in the second period. Restricted lines had a positive response in feed efficiency and negative response in consumption in both periods of selection. Changes in body composition in the first period reflected the changes in body weights through a lower crude protein percentage at the start of the period and a lower ash percentage at the end of the period. Body composition at the start of the second period was not altered by selection, while at the end of the selection period ad libitum lines had higher dry matter percentages and restricted lines had lower fat percentages. Body composition at 100 days of age was not affected by selection except for dry matter percent, that was lower in the restricted lines. / Correlated response in fitness was evaluated through litter size. In the first period lines selected under ad libitum feeding were not affected by selection for increased weight gain while selection for weight gain under restricted feeding caused a significant decrease in litter size.

Endothermy refers to the ability of an individual to produce heat from internal sources, and allows animals to maintain a body temperature that is higher than their external environment. Although much is known about the benefits of endothermy, its origin is highly debated. Nonetheless, due to environmental variation, endotherms have to regulate their heat production (thermogenesis) in order to remain normothermic. An endotherms regulatory response seems to be body size dependent. Keeping warm during cold periods is energetically expensive, and for small mammals this is exacerbated by their high rate of heat loss due to high surface area to volume ratios. To compensate for the heat lost, small non-hibernating mammals must increase their level of thermogenesis. Much of our current understanding of thermogenic responses of small mammals is derived from laboratory acclimated animals, and studies on naturally acclimatized animals are uncommon. In addition, most studies on thermogenesis tend to focus on one level of animal organisation, such as subcellular, tissue or in-vivo, but seldom integrate these data. The aim of this study was to measure year-round variation in thermogenesis across all levels of organisation, using naturally acclimatized Rhabdomys pumilio individuals from the Nelson Mandela Metropolitan University, Port Elizabeth. It was predicted that the level of thermogenesis would be significantly higher during winter relative to other seasons in order to cope with the low ambient temperatures (Tas) experienced during this season. Open flow respirometry was used to measure the animal's oxygen consumption, as a proxy for metabolism; the by product of which is heat production. The animal's basal metabolic rate (BMR), nonshivering thermogenesis (NST) capacity and summit metabolic rate (MSUM) were measured. A Western blot analysis was used to determine the expression of uncoupling protein 1 (UCP 1) in the animals' brown adipose tissue (BAT), as well as determine its relative concentration. The cytochrome c oxidase (COX) activity of the animals' visceral organs and BAT was measured, as an indicator of the tissues' metabolic activity. COX activity was determined as the difference in the tissues' oxygen consumption before and after the addition of horse cytochrome c.

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy