3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The evolution and diversification of diet in elapids(2016) Kgaditse, Mimmie MamafoloA central goal in macroecology is understanding the factors that have shaped broad-scale patterns among extant natural communities. Diet is widely cited as a key factor involved in shaping snake diversification. Amongst serpents, the adaptive radiation of elapids is unparalleled in terms of their sheer global distribution. My study was aimed at evaluating the variation in diet and how trends evolved throughout the radiation of the elapids. Based on the published natural history data of 303 elapid species, a cluster analysis revealed seven groups of species within which diet types were similar. The broad diet clusters included snake consumption, feeding on fish, ectotherms, endotherms, lizards, a generalist diet and lastly, a terrestrial invertebrate group that was the least prevalent diet type. Maximum Parsimony, Maximum Likelihood and Stochastic Character Mapping were used to trace the ancestral dietary condition in the Elapidae. Reconstructions demonstrated that starting from an ophiophagous ancestor, elapids still largely retain their early feeding habits. Despite the emergence of novel feeding patterns in the group, the predominantly conservative diet patterns suggest that niche conservatism has shaped elapid foraging dynamics. Members of the lineage characteristically feed on elongate ectothermic prey (e.g., squamates, caecilians, eels, earthworms) possibly owing to morphologically-mediated gape constraints. Phylogenetically corrected comparative methods were used to assess the influence of differences in body size, lifestyle and global scale spatial distribution of diet evolution. While lifestyle and distribution considerably influenced how diet patterns evolved, body size was not a significant determinant of the prey types taken. The lack of body size-diet association may be because larger-bodied elapids also opportunistically supplement their diet with smaller prey items. Overall, the findings indicate that recent ecological factors (e.g., lifestyle) coupled with long established factors (phylogeny, biogeography) have shaped elapid natural history patterns. This study is the first of its kind to offer a family-level, phylogenetically-based analysis on the evolutionary and contemporary feeding dynamics of the world’s most widespread snake family.Item Eating attitudes, body image satisfaction, and self-esteem of South African urban adolescents: the impact of acculturation(2015-04-20) Gitau, Tabither MuthoniIntroduction: An increase in the prevalence of eating disorders, body image dissatisfaction, low self-esteem and unhealthy weight control behaviors have been reported among adolescents worldwide, and are a public health concern with physical and psychological consequences. Although underweight and stunting still persists in South Africa, overweight and obesity is increasing in all ages, gender, and ethnic groups. Obesity is a biological risk factor for body dissatisfaction, low self-esteem and eating disorders among adolescents, all of which have been found to be associated with various weight change behaviors and strategies. South Africa being a culturally diverse country is undergoing rapid political, socioeconomic, nutrition and epidemiological transitions, and therefore offers a unique opportunity to investigate this area of research. Study design: There are two study components: (1) A cross-sectional study to determine gender and ethnic (black and white) differences in eating attitudes, self-esteem and body satisfaction in 13, 15 and 17 year-old boys (n=391) and girls (n=340) living in urban Johannesburg; (2) A longitudinal survey of the Birth-to-Twenty (Bt20) cohort at ages 13 and 17 years (n=1435) to compare eating attitudes, body-esteem and weight control behaviors between black and mixed ancestry adolescents, to examine the changes over time in these variables, and to investigate ethnic differences in the male and female perceptions of female body silhouettes at age 17 years. These ages were selected to provide a diverse sample of adolescents (early, mid and late adolescence). Methods: Anthropometric measurements were performed on all participants. Overweight and obesity were determined using age-gender specific cut-offs for BMI for children aged up to 17 years. Eating attitudes test-26 (EAT-26) scores were used to determine an increased risk of developing an eating disorder. The total EAT-26 score is the sum of the 26 items and scores range from 0 to 78. Participants who score more than 20 are considered to be at greater risk of developing an eating disorder, and represent more unhealthy attitudes towards food, body weight and eating. Body-esteem was measured using a body esteem scale. It consists of a set of 21 questions which measure 1) global feelings about one’s body e.g. “I like what I see when I look in the mirror”, 2) satisfaction with one’s weight e.g. “I really like what I weigh” and 3) positive evaluations about one’s body and appearance e.g. “People my own age like my looks”. The body-esteem assessment uses a 5-point scale ranging from “never” (1) to “always” (5) and the higher the score the more satisfied the participant is with their body. Total scores are divided into three categories; low body esteem (score 1 to 21), average body-esteem (score 22 to 42), and high body esteem (score > 43). The Rosenberg self-esteem tool was used to measure general self-esteem of the participants. Body image satisfaction tool was used to rate participants satisfaction with different parts of their body whereas, the body esteem scale was used to assess participant’s attitudes and feelings about their body and appearance. A series of randomly placed female silhouettes were used to assess participants association with different attributes. They were also asked to associate a series of randomly placed female silhouettes, with specific words or phrases including clumsy, happy, worst, strong, happiest, best, less respect, more respect, unhappy. All participants were asked a number of questions about their attempts to change their weight. Girls and boys were asked the following questions: “During the past year have you done anything to try to lose weight?”, “During the past year have you done anything to try to gain muscle?” If participants answered positively they were asked to give reasons, which included; health and cosmetic reasons e.g. to look better, clothes too tight, too fat, unhappy with self, and want to be a model. They were further asked about the methods they used to lose weight, and their responses were categorized into three groups: (i) healthy weight control behaviors (e.g. to exercise, eat more fruits and vegetables, and to eat less high fat foods and less sweets) [20] unhealthy weight control behaviors (e.g. fasting, eating very little food, skipping meals, cigarette smoking and use of food substitutes (iii) extreme weight control behaviors (e.g. use of diet pills, self-induced vomiting, use of laxatives and diuretics). Descriptive analyses were completed and stratified according to gender and ethnicity. For normally distributed data we used t-tests and ANOVAs, and for data that was not normally distributed Wilcoxon rank test was done to determine significant difference. Chi-square tests were used to determine differences between categorical data. Pearson correlation test was done to determine linear associations. A p-value of <0.05 was considered statistically significant. Results: In the non-cohort sample, the prevalence of overweight and obesity was higher in the white girls and boys compared to their black peers, significantly more black than white adolescents of both genders reported an EAT-26 score ≥20 (predisposition to an eating disorder). Although the prevalence of low self-esteem was greater in the white compared to black girls, in the study of the male adolescents, the low self-esteem was more prevalent in the black compared to the white boys. Significantly more black than white girls had high body image dissatisfaction (38.8 vs. 16.7%). There were significant differences between the male and female ethnic groups in their perception of female silhouettes, and the majority of the white girls (65.4%) wanted to be thinner compared to only 38.8% of the black girls. BMI was positively associated with self- esteem and negatively with dieting behavior in white boys , and with lower EAT-26 bulimic and oral control scores in black boys. In the Birth to Twenty cohort, black African females had a higher BMI (p<0.001) and an increased risk of developing eating disorders as well as significant increase in the prevalence of weight loss practices between the ages 13 and 17 years. At age 17 years both mixed ancestry adolescents had lower body-esteem compared to black adolescents. The prevalence of possible eating disorders was 11% and 13.1% in early and late adolescents respectively. Males and females shared similar opinions on normal silhouettes being the 'best', 'getting respect' and being the 'happiest', while the obese silhouette was associated with the 'worst' and the 'unhappiest', and the underweight silhouette with the "weakest". Conclusions: Black African urban teenagers seem to be embracing Western norms to fit in with the demands of Western culture, however there is still evidence of traditional influences in both boys and girls with regard to perceptions of female silhouettes. Our findings suggest ethnicity and gender play a major role in psychosocial disorders. Ethnicity and gender were found to be associated with an increased risk of future eating disorders, as well as weight loss and muscle gain practices. These findings are highly relevant for all African countries undergoing transition, and are important in planning the development of interventions to optimize adolescent health prior to adulthood.Item Effect of dietary Terminalia sericea aqueous leaf extracts on high-fructose diet fed growing Wistar rats(2014) Lembede, Busisani WisemanSedentary lifestyles and poor dietary choices are the major cause of the global increase in the prevalence of obesity and metabolic dysfunction in children. The high cost and limited access to conventional drugs by poor communities make them depend on ethnomedicines. Terminalia sericea (T. sericea) contains phytochemicals that give its extracts hypolipidaemic and hypoglycaemic properties hence its use in ethnomedicine to treat diabetes mellitus. Using weanling Wistar rat pups fed a high fructose diet to model growing children exposed to high-sugar diets, this study sought to evaluate the effects of aqueous T. sericea leaf extracts on their growth performance, glucose homeostasis, visceral morphometry and their general health profile. Forty 21-day old male Wistar pups were randomly allocated to five treatment regimens. Each group had ad libitum access to a commercially supplied rat chow. Group 1 pups were given plain drinking water and plain gelatine cubes, group 2: 12% fructose solution and plain gelatine cubes, group 3: 12% fructose solution and gelatine cubes containing fenofibrate at a dosage of 100 mg.kg-1 per day, group 4: 12% fructose solution and gelatine cubes with a low dose (100 mg.kg-1 per day) of the T. sericea extract and group 5: 12% fructose solution and gelatine cubes with a high dose (400 mg.kg-1 per day) of the T. sericea extract. The pups were maintained on the regimens for 12 weeks after which they under went an oral glucose tolerance test. Fasting blood metabolite content was then determined after which the rats were killed and tissues collected for visceral morphometrical, linear growth and surrogate markers’ of health determinations. T. sericea extracts had no negative effect on growth performance (body mass and indexes of long bone growth) but rats given fenofibrate had lighter empty carcasses and shorter tibiae. vi The administration of T. sericea extracts neither improved glucose homeostasis nor caused derangement of glucose handling by rats given a high fructose diet following an oral glucose challenge. However, the administration of fenofibrate to rats given a high fructose diet resulted in decreased glucose handling following an oral glucose challenge. With the exception of the administration of fenofibrate which resulted in a significantly high (P < 0.05) fasting blood glucose concentration, treatment regimens had no effect on fasting blood glucose, triglyceride and cholesterol concentrations. Rats given fructose with either plain gelatine cubes or low T. sericea dose had significantly higher (P < 0.05) liver lipid content compared with the control treatment. Administration of T. sericea extracts to rats given a high fructose diet had no effect on the GIT, other abdominal viscera and markers of general health. The administration of fenofibrate to rats given a high fructose diet caused increased relative mass of GIT organs (stomach, small intestine and caecum), increased absolute mass of other viscera (liver and kidney); increased serum phosphorus and alkaline phosphatase concentration. Results from the study revealed that administration of a high dose of aqueous T. sericea leaf extracts has potent phytochemicals properties that has helped to prevent high fructose diet-induced deposition of fat in the in the liver (non-alcoholic fatty liver disease), without compromising growth, visceral morphometry and general health of growing Wistar rats.Item Ecology and sexual selection of the common barking gecko (ptenopus garrulus)(2006-11-14T12:54:19Z) Hibbitts, Toby JarrellI investigated three mechanisms (endurance rivalry, contest competition, and mate choice) of sexual selection and the influence of multiple signals on intrasexual and intersexual encounters in the common barking gecko (Ptenopus garrulus). Aspects of the ecology of barking geckos were also studied to facilitate the investigation of sexual selection. Barking geckos exhibited sexual size dimorphism in relation to head size, with males having wider heads. No differences in diet or size of prey ingested were observed between the sexes, indicating that niche divergence was not occurring. Therefore, the difference in head width was best explained by sexual selection (male contest competition). Barking gecko diet was dominated by termites by number and volume. The peak reproductive season was in October for both sexes. I used activity patterns to determine if males emerged before females from winter dormancy, a key assumption of the protandry-based mating system model. Activity patterns were significantly different between males and females. Males were active in higher numbers early in the breeding season. Male and female activity patterns along with evidence that male territories were established before female emergence, testicular recrudescence likely coincides with male emergence, and larger males have larger territories and better reproductive success, suggest that barking geckos have a protandry-based polygynous mating system. I also tested for clustering of geckos on the landscape to determine if barking geckos lek. Clustering was found to occur in some instances, but barking geckos did not iii meet the criteria for a ‘classical’ lek species because males use calling sites containing resources (a burrow) that are also used by females. Lizards frequently rely on chemical cues to detect the presence of a conspecific. Male lizards in particular, may chemically sample potential refuges to avoid rivals. Barking geckos were equally likely to use an artificial refuge scented by another male compared to a control, indicating that males do not use scent when selecting refuges. I assessed the role of two signals, one acoustic (dominant call frequency) and one visual (yellow throat patch), in advertising residency and aggressive behavior in barking geckos. Larger males defended the largest home ranges and home ranges were maintained through calling, which is negatively correlated with body size. Body size also predicted some behavioural responses to field-playback trials. Small males retreated from the playback and large males were found to be aggressive towards the playback. Small relative throat patch size was also correlated with aggression and charging the playback. Finally, call frequency was correlated with the behaviour of charging the playback. I suggest that the frequencies of barking gecko calls constitute a long-range signal of body size, used by males for remote rival assessment and to advertise home range boundaries. I also assessed the role of multiple signals (acoustic and visual) in reproductive success and I studied the effect of one mechanism of sexual selection, endurance iv rivalry, on reproductive success. Activity levels were similar for males which bred compared to those that did not breed, suggesting that endurance rivalry is not a significant mechanism of sexual selection in this population. Body size was the best predictor of reproductive success, suggesting that call frequency functions as a long range signal of body size used by females to assess potential mates.