Primarily, this thesis attempts to resolve the debate concerning the factors selecting for the characteristic physiological traits of subterranean rodents. It also isolates the the probable causes of eusociality within the molerats (Bathyergidae). The bathyergids display the widest range of sociality of all mammals, from strictly solitary genera (Bathyergus, Georychus, Heliophobius), to social and eusocial genera (Cryptomys and Heterocephalus). Sufficient ecological data on key species (e.g., Cryptomys damarensis) were obtained to confirm trends in resource distributions associated with an aridity gradient and increasing sociality. This included data on resource characteristics, seasonal soil and burrow temperature regimes, burrow structures, colony structures, and the activity patterns of C. damarensis. Thermoregulation, including measurements of body temperature (Tb) and resting metabolic rates (RMR), was investigated for Bathyergus, Cryptomys, and Georychus, and compared with data from other workers obtained for Heterocephalus and Heliophobius. The cost of burrowing was measured for C. damarensis and H. glaber

Dissertation (PhD)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2006. / Zoology and Entomology / Unrestricted

Mole-rats from the family Bathyergidae are endemic to Africa, this family exhibits a continuum of sociality, comprising both solitary and social species. Sociality is related to the degree of aridity and the distribution of the underground food resource. All the members of the bathyergid family are strictly subterranean, and occur in a niche which is devoid of light cues and thermally buffered from ambient and surface extremes. Since vision is redundant in a lightless environment, mole-rats have subsequently undergone ocular regression over evolutionary time. As a consequence of the minute eyes, the visual system of mole rats is severely regressed and, in addition, the proportional retinal innervation to different structures is modified. The classical visual system is reduced while the circadian system is expanded. Retinal projection studies on the giant Zambian mole-rat, Cryptomys mechowi and an albino highveld mole-rat, Cryptomys hottentotus pretoriae, confirmed sparse contralateral retinal projections to structures of the visual system, while the circadian system received relatively dense bilateral innervation. The innervation pattern of an albino Damaraland mole-rat, Cryptomys damarensis differed from the other animals. Investigations of Fos expression in neurons over circadian time suggested that the phase response curve of the solitary mole rat, Georychus capensis, resembles that of aboveground mammals whereas the social Cryptomys hottentotus pretoriae, does not display differential sensitivity to light in the subjective day and night. The influence of increasing light intensities showed that higher light intensities elicit a more pronounced Fos expression in SCN of all the species investigated. In addition, longer light pulses also increases the Fos induction in the SCN. A preliminary investigation into the effect of temperature on the Fos induction in the SCN of three mole-rat species, demonstrated that a higher Fos response could be expected with higher ambient temperatures. However the sample size was very small, and could have influenced the outcome of the experiment. Behavioural locomotor activity rhythms of the solitary species, Georychus capensis, and the social species Cryptomys hottentotus pretoriae and Cryptomys damarensis, confirmed that activity patterns correlate with trends displayed in Fos expression. The solitary species exhibited much more defined rhythmicity than the social species and a higher percentage of the animals displayed distinct endogenous rhythms. African mole rats provide an interesting model to study not only the features of the circadian system in a group of animals with a naturally regressed visual system, but also the influence of sociality on the degree of regression. / Dissertation (MSc (Zoology))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

Please read the abstracts included at the beginning of chapters 2 to 5, of this document / Dissertation (MSc)--University of Pretoria, 2007. / Zoology and Entomology / MSc / Unrestricted

This PhD. thesis focuses on the vibrational communication of subterranean mammals, in particular, vocal communication of bathyergids (Heliophobius argenteocinereus, Fukomys mechowii, Fukomys darlingi) and seismic communication of Tachyoryctes. We recorded and analyzed the vocalization of three species and discussed the physical parameters of their vocalization in relationship to the special underground acoustic environment. Moreover, social systems of African mole-rats range from solitary to eusocial and thus our results enabled us to discuss the influence of sociality on vocal repertoire richness and its composition. Long distance communication possesses many challenges in underground environments; the only effective mean is seismic communication. We described for the first time seismic signaling in Tachyoryctes and proposed its function.

Please read the section 21chapter20, (Summary and conclusions), of this document / Thesis (DSc (Zoology))--University of Pretoria, 2008. / Zoology and Entomology / DSc / Unrestricted

The social reproductive inhibition evident in female common (Cryptomys hottentotus hottentotus) and highveld (Cryptomys hottentotus pretoriae) mole-rats was investigated, focussing on intra- and inter-subspecies differences in gonadotropin¬releasing hormone (GnRH) neuroanatomy and neuroendocrinology and potential mechanisms mediating social infertility through the suppression of luteinizing hormone (LH) and/or GnRH synthesis or release. The molecular structure of the GnRH peptide present in highveld mole-rat tissue was determined. Messenger ribonucleic acid (mRNA) coding for GnRH was isolated from hypothalamic tissue of a female highveld mole-rat. The nucleotide sequence of the transcribed complimentary deoxyribonucleic acid (cDNA) predicts amino acid sequences that indicate a potential polymorphism in the mature peptide. These sequences differ from classic 'mammalian' GnRH by either one or two amino acid positions. One form of mole-rat GnRH is identical to the unique GnRH expressed by guinea pigs, while the second form differs from guinea pig GnRH in one amino acid position. These results indicate that classic 'mammalian' GnRH is not the chief structural form of GnRH in the mole-rat. In both the common and highveld mole-rat, GnRH structures were loosely distributed along the septo-preoptico-infundibular pathway. Highveld mole-rats consistently had more GnRH cell bodies and higher levels of the peptide than common mole-rats. The subspecies also differed with regards to the relative distribution of GnRH cell bodies in the preoptic area and the medio-basal hypothalamus. Reproductive status and season did not influence GnRH neuroanatomy (numbers and morphology of cell bodies, distribution of GnRH structures and density of GnRH staining in the median eminence) or endogenous brain GnRH content in male or female common mole-rats. Likewise reproductive and non-reproductive male highveld mole-rats did not differ with regards to the GnRH neuroanatomical and neuroendocrinological parameters investigated. Dominant and subordinate female highveld mole-rats had similar numbers of GnRH cell bodies, and did not differ with regards to the distribution of GnRH structures. Brain GnRH levels was however significantly lower in reproductive females compared to non-reproductive females. Similarly, GnRH staining in the median eminence was significantly less intense in reproductive compared to non-reproductive females, indicating reduced release in the latter. Excess peptide most likely accumulates in the nerve terminals and the cell bodies. Endogenous opioid peptides (EOPs) are tentatively considered to playa role in the socially-induced infertility in non-reproductive female highveld mole-rats. Intact reproductive females and intact and ovariectmized non-reproductive females were treated with the opioid antagonist naloxone, alone and in different combinations with exogenous GnRH, to establish the role of EOPs and gonadal hormones in the reduced GnRH release evident in subordinate female highveld mole-rats. Naloxone treatment failed to alter plasma LH levels in any of the intact groups, while ovariectomized non-reproductive females showed a significant response. The pituitary response to a GnRH challenge was not influenced by either a single naloxone administration or longer term naloxone-priming regimens. In the absence of the negative feedback effects of gonadal steroids following ovariectomy, non¬reproductive females showed GnRH-chalienged plasma LH levels similar to that seen in intact reproductive females, both being significantly higher compared to intact non-reproductive females. Steroid-dependent mechanisms altering GnRH secretion and/or pituitary sensitivity to the endogenous peptide may therefore playa role in the social reproductive regulation displayed by the highveld mole-rat. EOPs may be indirectly involved in steroid negative feedback suppression of GnRH. In conclusion, the GnRH neuroanatomy and neuroendocrinology of female common mole-rats provide no evidence for a physiological component to the behavioural reproductive restraint in subordinate females due to incest avoidance. Non¬reproductive female highveld mole-rats are, however, temporarily infertile due to pituitary insensitivity to GnRH coupled with suppressed hypothalamic GnRH release potentially mediated by steroid-dependent mechanisms. / Thesis (PhD)--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Science, 2000.

Thesis (M. Sc.)(Zoology)--University of Pretoria, 2005. / Includes bibliographical references. Available on the Internet via the World Wide Web.