Instability characterizes the taxonomy of the African rodent subfamily Otomyinae. Two genera, Otomys and Parotomys, and 14 species are currently recognized, but the generic subdivision is equivocal. Between two and five cytotypes are delimited within O. irroratus, which illustrate a rapid rate of karyotypic evolution, and may reflect incipient speciation. In an attempt to resolve the group's phylogeny, the mitochondrial cyt b (complete) and 12S rRNA (802 bp) genes were analyzed using parsimony, distance and maximum likelihood methods. Alternative models of evolutionary change were compared to determine the best-fit model for each data set. Both genes failed to resolve deeper evolutionary associations, but the cyt b gene proved useful in resolving relationships among closely related taxa. Robust associations consistently retrieved include: (1) the O. irroratus cytotypes form a monophyletic group with O. laminatus basal. (2) an exclusively East African clade comprises two representatives of O. anchietae lacustris (not sister taxa), O. tropicalis with O. denti basal~ (3) Otomys angoniensis and O. maximus from southern Africa are monophyletic sister taxa with O. typus jacksoni and O. typus successively basal, making the East African Otomyinae non-monophyletic. (4) Parotomys brantsii and P. Wtledalei cluster within Otomys, but with no clear sister relationships. These results question some of the nomenclatural divisions in current use. First, the paraphyly of Otomys renders the recognition of two distinct genera unsupported. Second, the strongly supported monophyletic clustering of O. angoniensis and O. maximus coupled with the comparatively small genetic distance separating them, disputes the status of O. maximus. Third, the paraphyletic associations shown for representatives of O. typus and O. anchietae might imply that distinct evolutionary lineages are contained within these species. Otomys irroratus is phylogenetically distant from other Otomys species previously considered conspecifics. Moreover, a sister association between the Band C cytotypes to the exclusion of Al and A2, corroborate the delimitation of two major cytogenetic groups within O. irroratus. The major clades form an unresolved polytomy suggesting that the Otomyinae experienced a rapid radiation approximately 5 Myr ago. A biogeographical scenario is presented in light of palaeo-climatic changes during the late Miocene and Plio-Pleistocene epochs. / Thesis (DPhil (Zoology))--University of Pretoria, 2005. / Zoology and Entomology / unrestricted

In mammals, before fertilisation can occur, sperm have to bind to, and penetrate, the extracellular coat of the oocyte, the zona pellucida (ZP). In the laboratory mouse, which has been used as a model system for fertilization studies, sperm-ZP binding has been found to be mediated by a region near the carboxy terminal, encoded by exon 7 of the Zp3 gene. This region shows considerable interspecific sequence diversity in North American cricetid rodents, with some evidence of adaptive evolution, suggesting that this may contribute to species specific sperm-ZP binding. However, by contrast, in a preliminary study of three species of Australian murine rodents an identical protein sequence of the region encoded by exon 7 of Zp3 was found to be present. The aim of this present study was to determine the pattern of sequence diversity of this region in the most speciose subfamily of mammals, the murine rodents, and to obtain insight into the selective pressures involved in its evolution. For this, DNA was extracted from murine rodents of Africa, Eurasia, South-east Asia, New Guinea and Australia. The nucleotide and predicted amino acid sequence of exons 6 and 7 of Zp3 in 96 murine species from 14 divisions, as recently defined by Musser and Carleton (2005), was determined and compared. Generally, it was found that closely related species shared a highly similar ZP3 sequence. Maximum likelihood analyses of codon substitution models using representatives from 14 murine divisions, suggested that positive selection had occurred within only a few lineages at several different codon sites adjacent to, or within, the putative combining-site for sperm of ZP3. Positive selection was not evident when the analysis was restricted to the Australian taxa which showed low levels of both intra- and inter-generic sequence divergence. There was no good evidence that this region contributes to species specificity of sperm-ZP binding in these species. These findings thus suggest that the selective forces acting on the Zp3 exon 7 region during the evolution of the murine rodents have varied possibly due to a range of selective pressures not necessarily restricted to the prevention of hybridization. It seems unlikely, therefore, that the amino acid sequence of the exon 7 coding region contributes to species specificity of sperm-ZP binding within most of the lineages from this most speciose subfamily of eutherian mammals. / http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1294654 / Thesis(Ph.D.)-- School of Medical Sciences, 2007