- Title
- Genetic characterization of conspecific populations of Tilapia Sparrmanii (A.Smith 1840) in the dolomitic sinkholes and springs of the North-West Province (South Africa), and their comparison to Tilapia Guinasana (Trewavas 1936)
- Creator
- Nxomani, Clifford David
- ThesisAdvisor
- Kirby, Ralph
- Date
- 2002
- Type
- Thesis
- Type
- Doctoral
- Type
- PhD
- Identifier
- vital:4079
- Identifier
- http://hdl.handle.net/10962/d1007452
- Description
- This study was undertaken to investigate the genetic relationships of allopatric populations of the cichlid fish, Tilapia sparrmanii (A. Smith 1840) inhabiting the sinkholes and springs of the North West Province, South Africa. It also examined the genetic relationships of T sparrmanii to its polychromatic sister species, Tilapia guinasana (Trewavas 1936) which is endemic to the Guinas sinkhole in Namibia. Finally, the study investigated whether there is a genetic basis for T guinasana's colour polymorphism. The research was prompted by the concern of conservation authorities about the possible loss of unique fauna given the high demand for use of the subterranean waters for agricultural, domestic and industrial purposes. Such demands have the potential to drain these habitats. Further concerns related to habitat destruction and the introduction of alien species in the ecosystems inhabited by both fish species. Three approaches were adopted in attempting to answer the above questions. First was the investigation of Sodium dodecylsulphate (SDS)-Polyacrylamide Gel Electrophoresis (PAGE) of total cellular proteins as a fast and relatively inexpensive indicator of genetic relatedness between the fish populations. Secondly, genetic differentiation between the T sparrmanii populations and its relationship to T guinasana were assayed using restriction endonuclease analysis of Polymerase Chain Reaction (PCR)-amplified regions of the cytochrome b gene and the d-Ioop of mitochondrial DNA, coupled with Temperature Gradient Gel Electrophoresis (TGGE) analysis of the same regions. The third approach involved the use of Random Amplified Polymorphic DNA (RAPD) fingerprinting of the populations ofT sparrmanii as an indicator of genetic differentiation between them. RAPD fingerprinting was further used to investigate the genetic relationships between T sparrmanii and T guinasana and to probe the genetic basis of the polychromatism of the latter. SDS-PAGE did not reveal any genetic differentiation between the T sparrmanii populations, nor could the analysis detect variation within them. It however clearly distinguished at a species level between T sparrmanii and T guinasana as well as between these and other fish species, thus indicating its possible utility as an indicator of genetic relatedness at a species level. Mitochondrial studies employing the Restriction Fragment Length Polymorphism (RFLP) of Polymerase Chain Reaction (PCR)-amplified cytochrome b (1.1 kb) and d-Ioop regions (0.9 kb) with six and five restriction enzymes respectively, failed to reveal genetic differences within and between the allopatric populations. TGGE of500 bp of the d-Ioop and 400 bp of the 12sRNA PCR-amplified fragments did not reveal any differences between the populations of T. sparrmanii, nor did the analysis reveal any differences between T. sparrmanii and T. guinasana. The lack of differentiation between the T. sparrmanii populations by these mitochondrial Dna analysis techniques, despite habitat fragmentation, indicated a recent origin of the populations from a common ancestral population. Failure to distinguish between T. sparrmanii and T. guinasana may be related to the sensitivity of the techniques utilized. RAPD fingerprinting analysis indicated that the populations are genetically differentiated from each other. Using a measure of coefficient of variation, the population with the highest variation was the Wondergat population (13.99%), followed by the Klerkskraal popUlation (8.29%), the Malmani and Marico Oog populations (each with 5.88%) and the least variation (4.95 and 4.83%) was with the Amalinda and Molopo Oog populations respectively. This high degree of intra population similarity points to the fact that this differentiation is still confined within the limits of con specificity. The genetic distances between all of the T. sparrmanii populations across all primers ranged from 0.09 to 0.234 and averaged 0.146, a value that falls in the upper end of conspecific population differentiation. Such results indicate populational sub-division below the species level. RAPD fingerprinting therefore proved more sensitive than protein or mitochondrial studies. The differentiation it detected between the populations is a reflection of their adaptation to local conditions of the unique ecosystems they inhabit. A comparison with a subset of primers between T. guinasana and T. sparrmanii confirmed the separate species status of the former from the latter. The mean genetic distance between the T. sparrmanii populations was 0.136, compared to that between T. sparrmanii and T. guinasana which was found to be 0.374. Statistical analysis of the difference between the mean genetic distances indicated significance with 95% confidence. The polychromatism of T guinasana was investigated to determine whether there were significant differences between its five colour morphs. RAPD fingerprinting indicated with 95% confidence that there were significant differences between the colour forms based on the genetic distances computed between them. These genetic differences appeared to correlate with the observed assortative mating between the colour forms of the species. The manifestation of the polychromatism at sexual maturity in T guinasana probably indicates that colouration plays an important role in the breeding process. The genetic uniqueness shown here between the populations of T sparrmanii and the colour forms of T guinasana indicate for protective measures to be put in place if the genetic resources of the isolated fish populations are to be preserved. These must be coupled with a thorough assessment of the temporal and spatial distribution of genetic variability of the populations as a guide to a long-term management strategy for the fish populations and the ecosystems they inhabit. This study therefore has shown that the allopatric populations of T sparrmanii in the sinkholes and springs of the North-West Province are genetically unique, as well as show that the colour forms of T guinasana are genetically distinct.
- Format
- 193 leaves, pdf
- Publisher
- Rhodes University, Faculty of Science, Biochemistry, Microbiology and Biotechnology
- Language
- English
- Rights
- Nxomani, Clifford David
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