Thesis (MSc (Botany and Zoology))--Unkiversity of Stellenbosch, 2009. / Phylogeographic genetic structure has been documented for a number of southern African terrestrial taxa.
Information regarding geographic population genetic structuring in multiple taxa, with differing life
histories, can provide insights into abiotic processes such as vicariance. A fragment of the cytochrome b
mitochondrial DNA gene of a plains-dwelling species, Otomys unisulcatus, was sequenced and analysed.
Two closely related geographic assemblages were found. The first assemblage (lowland group) contains
populations from both the eastern and western parts of the species range, and the second comprises
populations from the Little Karoo (central group). The lowland group was shown to be in a state of
population expansion after a relatively recent mitochondrial DNA (mtDNA) coalescence, while the genetic
signature of the central assemblage was characterized by more genetic diversity indicative of an older
lineage/genetic refuge. Areas of higher elevation (namely mountain ranges) appeared to be the main factor
limiting gene flow between these two groups. Aridification cycles due to glacial maximum periods
probably resulted in increased dispersal leading to the widespread distribution of common haplotypes
throughout the lowland group.
Morphological variation in skull shape and size has been shown to follow environmental clines in some
rodents. Geometric morphometric analyses on the ventral and dorsal views of the craniums of O.
unisulcatus were utilised to test whether the population groupings obtained in the genetic analyses would be
recovered by morphometric analyses. In addition, it was also investigated which of the environmental
factors investigated influenced skull shape and size. The genetic groupings were not recovered for either the
cranial shape or size. Size variation in the females correlated positively with annual rainfall, and so by
proxy with habitat productivity, indicating that females which inhabited areas with lower rainfall would be
larger. The significant relationship between females’ centroid sizes and rainfall was thought to be as a result
of the increased nutrient requirement by this gender in the production of offspring. The males did not show
a significant correlation between any of the environmental variables and centroid size. There was a
significant difference between the skull shapes of the genders, further verifying the sexual dimorphism in
the species. Three major clusters were found (according to cranium shape) using a Two-Block Partial Least
Squares Analysis (2B-PLS), which relate to the biome boundaries within the species’ range. Variations in shape were attributed to the varying needs for strong masticatory muscles resulting from differing diets.
The skull shapes of specimens occurring along the escarpment were intermediate between the first two
clusters. Cranial shape in the male dorsal view dataset was significantly correlated with the environmental
variables block, possibly due to the much lower minimum temperature in the Sutherland population (a
population which was not included in the female analyses). It was concluded that differing diets of
individuals in the respective biomes influenced the shape of the cranium of both genders. The sexual
dimorphism in the cranium shapes may be as a result of the females digging tunnels (using their teeth)
underneath the stick nests. Otomys unisulcatus show high levels of phenotypic plasticity throughout the
range and it thus appears that the species can adapt fast to the different environmental variables.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2108 |
| Date | 03 1900 |
| Creators | Edwards, Shelley |
| Contributors | Matthee, Conrad A., Jansen van Vuuren, Bettine, University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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