3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Nongeographic variation in the striped mouse Rhabdomys dilectus chakae (Rodentia: Muridae)(2018) Neves, Candice NikitaThe morphological variation between populations is shaped by adaptive responses to prevailing environmental conditions and/or not adaptive stochastic effects. Within-population variation is mainly related to age and sexual dimorphism, as well as temporal and spatial variation in environmental conditions. The aim of this study was to investigate patterns of variation in the skull, mandibles, and dentition in a population of the African four-striped mouse Rhabdomys dilectus chakae. Geometric morphometrics was used to assess the variation related to allometry and age, sexual dimorphism, and the inter-annual variation between specimens collected in different years (1975, and 1994-1997). A review of the literature on the application of geometric morphometrics to rodent morphological variation was conducted and landmark morphometrics were concluded to be the most appropriate methods for the skull and the mandible analyses, with a separate analysis using landmarks and semi-landmarks to analyse the variation of mandibular curves, and outline morphometrics with an Elliptic Fourier analysis of the upper molars. Images of the skull (ventral and lateral view at 5x magnification), mandible (at 6.8x magnification), and the three left upper molars (at 10.5x magnification) were captured using a stereoscopic microscope. Landmarks were digitized on the skull and mandible images, with semi-landmarks digitized on mandible images, and outlines were digitized on molars. Multivariate analysis of variance was used to analyse shape and size variation due to age, sex, and year of sampling and a multivariate regression was used to analyse allometry. A PCA was used to visualize shape variation, and boxplots of log-centroid size to visualize size variation between age classes, sexes, and years of sampling. Shape variation was significantly predicted by age and year of sampling, while size was significantly predicted by age, sex, and year of sampling. Size significantly contributed to shape variation, although size alone did not appear to explain much of the variation present. Most age-related variation in shape was due to differences between the first three age classes and age class IV, while size increased with increased age (i.e. growth). Males were larger than females although no sexual shape dimorphism was evident between sexes. Typical of species with male-male competition, Rhabdomys dilectus chakae demonstrated sexual size dimorphism; larger males have greater mating opportunities. Specimens from 1994 and 1997 had more variable shapes and were consistently smaller than those collected in 1975, 1995 and 1996, except for dentition where these latter specimens were smaller than those collected in 1994 and 1997. Annual variation in morphology may be a plastic response to prevailing local climatic conditions (i.e. rainfall and temperature), Masters Dissertation Candice Neves iv resulting in annual variation in diet, affecting the skull and dentition. Further studies should consider more populations in the species to assess the generalizability of the findings, particularly annual variation, and to consider spatial variation across the distribution of a population.Item The behavioural ecology of bachelor male groups in the African striped mouse, Rhabdomys pumilio(2018) Kanyile, Sthandiwe NomthandazoMales in several animal species vary in traits which confer competitive ability. Younger and old, small and large males thus regularly make use of different behavioural tactics (i.e. alternative reproductive tactics, ARTs) in order to secure mates and increase their fitness. In the Succulent Karoo, males of the African striped mouse Rhabdomys pumilio adopt one of three main ARTs, i.e. philopatric, roaming, or territorial tactics; the tactic chosen is influenced by body mass. Additionally, the occurrence of bachelor groups (two or more males sharing a nest without any female) in striped mice has recently been observed. The present study was concerned with investigating the composition and function of these bachelor groups in striped mice, especially to assess whether they represent a fourth ART. For this, I used data collected from 2009 to 2016 to determine the season (breeding versus non-breeding) during which bachelor groups occurred and how they originated. At the start of the breeding season, I compared bachelor males with the known ARTs with regard to their scrotality, body mass, and age. I also determined the tactics of bachelor males before and after they were bachelors, and whether these tactic changes were associated to changes in body mass. My results indicate that bachelor groups are mainly formed by unrelated philopatric males which have dispersed from their natal groups. These groups most frequently occur in the breeding season, when population density is low to intermediate. Bachelor males occupy the intermediate position in the body mass spectrum in striped mice, being heavier than philopatrics but lighter than breeders, and do not differ in body mass from roamers. After the bachelor tactic, more males employed the roamer than the territorial breeding tactic. I hypothesise that the bachelor tactic is a “transitional tactic” which facilitates the change from a low fitness tactic (philopatric) to a higher fitness tactic (roaming or breeding) by allowing relatively small males to cooperate in social thermoregulation. These findings provide valuable insight on a phenomenon which has not been studied before in striped mice. Keywords: African striped mouse, alternative reproductive tactics, bachelor, behavioural plasticity, group-living, social flexibilityItem The behavioural and neuroendocrinological mechanisms affecting group formation in the African striped mouse, Rhabdomys(2018) Hartman, Kirsty-JaneSocial systems vary within and between species, resulting in some populations living in complex social groups while others adopt a solitary lifestyle. Social systems are ultimately emergent properties of the interactions and relationships between individuals within a population. Social flexibility (a form of phenotypic plasticity) describes hormonally mediated reversible switches in social tactic in response to prevailing environmental conditions. I investigated the mechanisms underlying social interactions, and ultimately social structure in the striped mouse genus, Rhabdomys. It is widespread in southern Africa, occurring along an aridity gradient, which influences the social structure of constituent species. A desert species, R. pumilio, switches from group to solitary-living, and I asked whether a solitary-living grassland species, R. dilectus, could form stable groups. Four experiments were undertaken. 1) To examine the behaviours underlying group formation initiation, age-matched triads of unrelated, sub-adult conspecific female grassland and desert striped mice were formed in captivity. Nest-cohabitation occurred in all desert and 90% of grassland triads, yet desert triads were more aggressive than grassland triads on initial meeting. Both species spent more time interacting amicably as time in triads progressed. 2) Measurements were taken of circulating corticosterone and testosterone concentrations, and 3) neuropeptide arginine vasopressin (AVP) and oxytocin concentrations in the brain of triads and singly-housed controls. Grassland females in triads had greater corticosterone and AVP concentrations than desert female triads, but levels did not differ between triads and solitary-housed controls of both species; testosterone and oxytocin were unaffected. 4) I experimentally injected females of both species sequentially with a saline control, a low and a high dose of AVP, and measured their social motivation (i.e. propensity to spend time with a conspecific) and recognition of familiar unrelated conspecific females. Exogenously administered AVP enhanced the motivation to be social, by increasing the approaches toward the conspecific by focal females in the high AVP treatment in grassland mice and the low AVP treatment in desert mice. Neither species displayed a preference for an unfamiliar conspecific, but amicability toward familiar females was greater in grassland mice, but decreased in desert mice, under high AVP. Solitary grassland striped mice displayed tolerance of conspecifics, underpinned by different inherent hormonal control. My study has demonstrated that the naturally solitary R. dilectus can form similar social groupings to that of the facultatively social R. pumilio. Switching between social tactics might have potential survival benefits in unpredictably changing environments predicted for southern Africa.Item Behavioural correlates of stereotypic behaviour in Rhabdomys dilectus(2018) Silber, SarahThe specific causal mechanisms of stereotypies are difficult to establish, especially because they do not develop in all individuals of a species living in the same captive environment, and may be affected by other behaviours (e.g. personality) and the life history of the animal. The overarching aim of this study was to investigate the behavioural correlates of stereotypic behaviour in the striped mouse Rhabdomys dilectus, and to ascertain whether there are any specific traits associated with stereotypic behaviour in this species. I studied the behaviour of stereotypic and non-stereotypic striped mice in four behavioural assays, including: (1) general home cage behaviour; (2) dyadic encounters to assess social interactions; (3) personality tests to measure interindividual variation in behaviours; and (4) perseveration tests by means of a plus maze. Results indicated that: (1) stereotypic striped mice showed higher frequency and duration of active behaviour and higher rates of inactivity, whereas non-stereotypic mice displayed longer durations, but fewer occurrences, of inactivity; (2) social motivation was not a predictor of stereotypic behaviour in striped mice; (3) Stereotypic mice showed a proactive coping style typified by spending a longer time in the light compartment after a startle response, a greater manipulation of novel objects in the home cage, and increased activity levels in standard housing. Non-stereotypic mice showed a reactive coping style typified by greater anxiety and fear toward novel objects, and heightened inactivity; and (4) levels of perseveration were higher in stereotypic striped mice. I also found that stereotypic mice that showed higher frequencies and durations of activity also displayed a proactive coping style and were more preservative. In addition, non-stereotypic mice that were inactive for longer showed a reactive coping style and lower levels of perseveration, which suggests inactivity is a possible alternative response to stereotypy in captive environments. In conclusion, stereotypy, activity, personality, and coping style appear to have common underlying, possibly neurobiological, mechanisms. In particular, I hypothesise that dysfunction of the basal ganglia, or suppression of the indirect (striatopallidal) pathway, results in inappropriate repetitive responses and stereotypic behaviour. Further research is needed to measure brain hormones and structure in order to determine the nature of the imbalances and whether they are consistent within and between species. In addition, investigations are required of factors which may mediate these imbalances, including age of weaning and other genetic influences.Item Behavioural adaptive variation in the striped mouse Rhabdomys(2017) Mackay, Megan KirstenUnder current and previous global climate change, environments are changing and have changed at a rapid rate. Species with the potential to undergo adaptive radiation are likely to survive environmental change. The genus Rhabdomys is widespread in southern Africa, occurring along the east-west rainfall gradient in South Africa. Rhabdomys may have undergone adaptive radiations in the past, which may have resulted in the current suite of species in various habitats of different aridity. Some Rhabdomys species also occur in sympatry in some locations in South Africa. The aim of my study was to investigate adaptive variation in Rhabdomys by studying the behaviour of 5 populations, representing 3 Rhabdomys species, across South Africa. Using selected taxa, my approach was, firstly, to describe variation in two traits, personality and spatial cogntion, well known for showing environmentally-linked (i.e. adaptive) variation. Secondly, I manipulated the development of exploratory and anxiety behaviour to assess the limits of the adaptive variation (i.e. test the nature of the reaction norm of the characters measured). I first established the taxon-level personality of 4 taxa (2 sympatric) in 5 standard behavioural tests. Generally, the semi-desert living R. pumilio was the boldest together, surprisingly, with R. d. dilectus occurring in grasslands of central South Africa, contradicting previously published results. Comparatively, R. bechuanae from central South Africa and R. dilectus from far north-eastern South Africa, also occurring in grasslands were less bold, even though R. bechuanae is sympatric with R. dilectus in central South Africa. My data indicate adaptive variation at the extreme populations and possibly character displacement in the sympatric populations. In the next chapter, I investigated whether early rearing environment shapes exploratory behaviour and anxiety responses of R. pumilio and R. bechuanae. I predicted that using an interspecies cross-fostering protocol would reveal a gene x environment interaction on behaviour, so that fostered offspring would display an intermediate behaviour phenotype compared to their non-fostered siblings. I showed that a novel rearing environment mostly did not influence the adult behaviour of cross-fostered inidividuals. This indicates genetic constraints on exploratory behaviour and anxiety responses. Next, I tested whether physical rearing environment shapes exploratory behaviour and anxiety responses. I reared semidesert R. pumilio, sympatric R. bechuanae and R. dilectus and allopatric R. bechuanae under either no cover or high cover for 2 generations. The taxa were mostly similar and altering the phyical housing condition did not alter behaviour, but there were small differences between the taxa in exploratory behaviour. In the final experimental chapter, I established whether the environment predicts the spatial cognition in semi-desert R. pumilio, sympatric R. bechuanae and R. dilectus and an allopatric population of R. dilectus from far north-eastern South Africa. The populations showed very similar performance in a modified Barnes maze, indicating a possible phylogenetic constraint on spatial cognition. Overall, my study suggests that there is adaptive variation in personality but not spatial cognition. In contrast to previous studies in the genus, alterations to the social and physical environments failed to separate out genetic and environmental effects (i.e. reaction norm) that would potentially provide the mechanisms for adaptive variation within and between species. The similarity in spatial cognition between taxa and similar responses to environmental modification indicate phylogenetic constraints on traits that were predicted to vary geographically.Item Pre-clinical evaluation of pneumococcal vaccine candidate molecules in a mouse pneumococcal pneumonia model(2016) Lebogo, Kgomotso WelheminahBackground: Streptococcus pneumoniae (pneumococcus) is a major cause of morbidity and mortality in young children. Pneumococcal conjugate vaccines are restricted in their serotype coverage, and hence, focus has been directed towards common protein-based antigens. However, there have been problems associated with testing protein-based antigens in animal models. These include inhumane endpoints, use of large sample sizes, and the inability to detect subtle differences between antigens. This study describes a novel intranasal pneumonia co-inoculation model conducted in mouse and aims to address some of these limitations. Methods: Eighty female NMRI mice were equally distributed into the vaccinated and placebo groups. The mice were subcutaneously inoculated with recombinant PspC or PpmA or adjuvant (control). Both groups were co-inoculated with 50 μL of a bacterial suspension containing D39:: rpsL (serotype 2) or PJ351:: rpsL (serotype 1) wild-type strains and their isogenic knockout strains containing a trimethoprim resistance marker. Mice (n = 5 per group) were terminated at 0, 6, 12 and 24 hours post-inoculation. Bacterial samples were obtained from nasopharyngeal washings, bronchoalveolar lavage fluid (BAL fluid) and homogenised lung tissue. Bacterial counts were obtained from selective media containing either streptomycin or trimethoprim, and the ratios of wild-type and knockout were determined. Serum was collected by cardiac puncture and ELISA was used to monitor the levels of IgG antibodies. To further refine the model, a single time point (T = 24h) in which events were more pronounced was chosen for the rest of the experiments and the number of mice was scaled down to 20 mice per experimetal procedure. A group of 20 mice (10 in placebo and 10 in vaccinated mice) were subcutaneously vaccinated with either recombinant PspA, IgA protease and SlrA or adjuvant (control). Both vaccinated and adjuvant groups were co-inoculated with 50 μL of a bacterial suspension containing D39:: rpsL (serotype 2) or PJ351:: rpsL (serotype 1) wild-type strains and their isogenic knockout strains. Bacterial samples were collected from mice as described above. Results: Pneumococcal knockouts of D39 and PJ351 lacking the genes encoding PpmA and PspC were attenuated in their ability to colonise the nasopharynx, BAL fluid and lungs of mice. Knockouts deficient in PspA, IgA bacterial protease and SlrA in the PJ351 background were attenuated in all sites sampled, whereas knockouts in the D39 background were attenuated only in the nasopharynx. PspC IgG antibodies were able to elicit clearance of PspC producing wild-type D39 and PJ351 strains more effectively compared to PspC deletion knockouts, which were able to persist in the nasopharynx, BAL fluid and lungs. Responses in PpmA vaccinated mice were dependent on the genetic background of the inoculation strains. Clearance of D39 wild-type strains was more noticeable in the nasopharynx than in the BAL fluid and lungs, whereas the wild-type PJ351 was cleared more efficiently than the knockout in the BAL fluid and lungs, compared to the nasopharynx. Responses in IgA bacterial protease vaccinated mice were also dependent on the genetic background of the inoculation strains, with a clearance of the D39 wild-type strain being more noticeable in the nasopharynx. PspA and SlrA IgG antibodies were not protective against infection with both strains of the pneumococcus in the mouse model. Conclusion: Using PspC, PpmA, PspA, IgA bacterial protease and SlrA as examples, we demonstrated that this mouse co-colonisation model could effectively detect subtle differences in the clearance of wild-type and knockout bacteria in the presence of antibodies against non-essential surface antigens. The model is humanely more acceptable, as it uses far fewer animals than conventional testing, with greater sensitivity. Further, it relies on measurements of bacterial density, rather than fatal disease as endpoints. The model also provides additional benefits in terms of monitoring the virulence characteristics of the target antigens.Item Epigenetic inheritance of aberrant DNA methylation signatures as a consequence of chronic paternal alcohol exposure and the effect on embryonic gene expression in mice(2015) Ismail, AyeshaEpigenetic mechanisms regulate gene expression, a particularly important activity during foetal development. DNA methylation contained within promoter and regulatory intergenic regions influence gene activity. In utero alcohol exposure as a result of maternal consumption during pregnancy has been associated with disruption of foetal DNA methylation and gene expression, leading to neurological dysfunction, growth retardation and facial anomalies. While similar phenotypes in offspring have been associated with chronic preconception paternal alcohol exposure, the mechanisms underlying these effects remain largely unexplored. This study aimed to: (1) validate significant changes in sperm DNA methylation in a list of ten candidate genes in male mice chronically exposed for ten weeks to ethanol (n=10) compared to a calorie-equivalent sucrose solution (n=10); (2) validate significant changes in gene expression in candidate genes in the brain, liver and placenta of E16.5 embryos sired by ethanol (n=24) compared to sucrose (n=24) treated male mice; (3) quantify DNA methylation changes in candidate genes in the three embryonic tissues. (4) Lastly, previously generated microarray data were reanalysed using bioinformatics tools to generate a top ranked candidate differentially expressed gene list that was used to identify and analyse biological functions or pathways significantly over represented among these genes using PANTHER and DAVID. This study was unable to provide validation for most of the significant differences observed in the sperm DNA methylome in the original study, most likely because of the low sperm DNA concentration. Significant methylation differences were however observed at individual CpG sites in three candidate genes (Igf1r, Odc1, Depdc1b) in specific tissues of embryos sired by ethanol-exposed males relative to embryos sired by sucrose-treated males. There was concordance in the direction of altered gene expression between the cases and controls using the microarray and real-time PCR approaches for two genes in the brain (Grm7 and Zfp317), three genes in the liver (Igf1r, Vwf and Depdc1b) and one gene in the placenta vii (Vwf). However, none of the candidate genes selected for validation showed statistically significant changes. This may be a result of the modest fold changes observed in the microarray experiment that as shown in many cases, often do not replicate. The remainder of the genes showed no changes in expression in the test embryos relative to the control. The functional enrichment analysis revealed biological processes that were over represented in the brain and liver indicating that they may be more vulnerable to the effects of alcohol, compared to the placenta. Overall, the study could not provide a statistically significant correlation between methylation changes in the sperm that were inherited by the offspring which subsequently dysregulated gene expression in the embryo. However, as trends toward significance and significant DNA methylation changes were observed in the embryonic tissues, this study supports the idea that preconception paternal alcohol exposure can induce epigenetic alterations in a locus and organ specific manner within offspring.