3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The behaviour of two sub-species of the striped mouse Rhabdomys: the role of phylogeny and the environment(2011-09-14) Mackay, Megan KirstenThe role of phylogeny and environmental influences on behaviour were investigated in two sub-species of Rhabdomys dilectus: R. d. chakae and R. d. dilectus. I compared populations of the two sub-species that occur about 70 km apart in superficially similar grasslands, south of Johannesburg (Walkers Fruit Farms) and at Irene in Gauteng Province, South Africa. The vegetation characteristics of the localities were assessed by measuring aerial cover, cover density, amount of dead material, and the maximum and minimum plant height. I studied the maintenance (non-social) and social behaviour of the sub-species in captivity. Three maintenance behaviours were studied: diel activity in an open arena, activity in an enclosed maze and in a modified plus maze. Social behaviour was studied by investigating the stress response of juvenile males after removal from their family groups and being placed in a plus maze, and the tolerance of unfamiliar same-sex consub-specifics in staged dyadic encounters. My results indicate that there were differences in the vegetation at the localities, most notably in the level of cover, which was greater at Irene (R. d. dilectus) than at Walkers Fruit Farms (R. d. chakae). Both sub-species displayed similar activity profiles (diurnal and crepuscular) and similar levels of activity in an enclosed maze. However, R. d. dilectus showed high levels of anxiety in an open arena and in a plus maze. The sub-species showed similar social behaviours: males of both sub-species that were removed from their family groups at the onset of weaning showed a lower stress response compared to the social sister species R. pumilio. Social interactions of same-sex intra-sub-specifics were mostly similar between the sub-species but there were slight discrepancies in behaviour associated with mating. Surprisingly, there were higher levels of amicability in all dyads than predicted by the solitary lifestyle of the two sub-species in nature. Behavioural differences (anxiety response) may be due to divergence in allopatry because of differences in vegetation characteristics. The similarities in activity profile and social behaviours could be explained by phylogenetic inertia or by similar selection pressures in similar environments.Item Reproductive isolation in the striped mouse Rhabdomys: a case for reinforcement?(2007-02-23T12:52:54Z) Ahamed, Ahamed Mohaideen RiyasReproductive isolation was investigated in two chromosomally distinct populations of Rhabdomys on the Gauteng highveld. The two populations, Midrand (2n = 48) and Irene (2n = 46), occur 15 km apart, with no known contact or hybrid zone between them. Behavioural experiments, comprising male-female dyadic encounters and female preference tests for same-and different-population male odour, were used to test for premating barriers. Aggression levels were highest in different-population than same-population dyads, and females spent more time with odours of males from their own population than of those of the other population. Breeding and postnatal development studies were conducted to establish postmating barriers. Compared to different-population pairs, reproductive success was markedly reduced in different-population pairings, and the few hybrids that were produced did not breed. My studies indicate that behavioural isolation is well-developed between the Midrand and Irene striped mice, and suggest that the mate recognition system has diverged in allopatry, which would reduce gene flow between the two populations. Such divergence supports the findings of mtDNA studies by other workers who proposed that the two chromosomal forms used in my study represent two subspecies of R. dilectus. Previous studies showed that distant striped mice populations (>900km) displayed behavioural divergence and intermediately located populations (~80km) were behavioural compatible but had hybrid failure; the Irene population was used in both studies. In comparison, the behavioural incompatibility between the closely-located Midrand and Irene populations provides support for the reinforcement of previous postmating isolation seen in the intermediately located populations, particularly since no contact or hybrid zone exists between the two forms. However, I cannot rule out other explanations, such as dissimilar ecological conditions, influencing interfertility.Item Stereotypical behaviours in the striped mouse Rhabdomys pumilio: evaluating the coping hypothesis(2006-11-15T11:28:03Z) Van Lierop, Mathew CarlStereotypic behaviours are repetitive invariant behaviours that serve no obvious purpose and are common in both domestic and non-domestic captive animals. Stereotypies are regarded as indicators of poor welfare although the growing body of work pertaining to these behaviours has challenged many previously held notions of stereotypy. The most widely accepted, although frequently contested, hypothesis used to explain stereotypies is the coping hypothesis, which states that animals perform stereotypies to cope with the stress of adverse environments. The aim of my study was to investigate the fitness effects of stereotypy, and whether or not environmental enrichment protocols were effective in reducing or eliminating stereotypy in the adult striped mouse Rhabdomys pumilio. Both of these experiments were designed to evaluate the coping hypothesis. I intentionally used wild caught and F1 individuals to eliminate any potential captive selection bias that may exist in extant captive populations that could affect interpretation of fitness. For the first aim, 40 breeding pairs were assigned to one of four treatments: 1) stereotypic female and stereotypic male (S-S); 2) stereotypic female and non-stereotypic male (S-NS); 3) non-stereotypic female and stereotypic male (NS-S); and 4) non-stereotypic female and non-stereotypic male (NS-NS). Compared to non-stereotypic females, stereotypic striped mice females had better reproductive output, including larger litter size, higher growth rate, higher litter survival, shorter interlitter interval and shorter time to first litter. Reproductive success was higher in S-S and S-NS pairs, indicating that genetic and maternal effects jointly determined fitness in striped mice. Unlike other published research, maternal mass was not a predictor of fitness. For the second aim, I housed 20 non-stereotypic and 20 stereotypic striped mice (equal sex ratio) in barren cages for 60 days, and transferred them to enriched cages, and repeated this experiment with striped mice housed initially in enriched cages and transferred to barren cages. While there was a measurable reduction in stereotypy in individuals transferred from barren to enriched environment cages, no increase in stereotypy was noted in striped mice transferred from enriched to barren cages. These findings appear to concur with the coping hypothesis, that stereotypies become perseverative (e.g. bad habits) and difficult to disrupt. Non-stereotypic striped mice were not influenced by the swap. I conclude that the expression of stereotypy is a potential sign of positive welfare and that it may be worthwhile to specifically elicit stereotypic behaviours in order to improve the welfare, and in certain cases, breeding success, of captive animals. Moreover, I maintain that where necessary, effort should be applied to combating stereotypies before they arise, rather than attempting to eliminate them once they have actually developed.