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Evolutionary genetics of the Begonia dregei Complex (Begoniaceae)

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dc.contributor.advisor McLellan T en
dc.contributor.advisor Balkwill K en
dc.contributor.author Matolweni LO en
dc.date.accessioned 2016-09-22T11:14:08Z
dc.date.available 2016-09-22T11:14:08Z
dc.date.created 1995 en
dc.date.submitted 2001 en
dc.identifier.uri http://hdl.handle.net/20.500.11892/106312
dc.description.abstract The <i>Begonia dregei</i> complex (Begoniaceae) is endemic to isolated coastal forest patches of eastern South Africa. This dissertation employed an interdisciplinary approach and investigated the evolutionary genetics of the <i>B. dregei</i> complex focusing on two of the major topics in evolutionary biology, population genetics and phylogenetics. Difficulty in the reconstruction of phylogenetic relationships within the complex, however, has been a long-standing problem and only <i>B. dregei</i> and <i>B. homonyma</i> are currently recognized as species. The distinction between B. dregei and <i>B. homonyma</i> has been entirely based on differences in the shape and size of leaves. Leaf shape is similar within populations but differs consistently between patches of forest. Population genetic studies concentrated on investigating and addressing questions related to the amount and distribution of genetic diversity and gene flow among populations. The phylogenetic study on the other hand was aimed at establishing whether patterns of relationships are consistent with the current taxonomic treatment. A strategy to combine multiple sources of data and thus increase the phylogenetic signal in the <i>B. dregei</i> complex was investigated, using a technique called matrix representation using parsimony analysis (MRP). The population genetic structure was determined by analysis of 15 enzyme loci. Sequences of the internal transcribed spacer (ITS) and <i>trn</i>L (UAA)-<i>trn</i>F(GAA) intergenic spacer regions of the nuclear ribosomal and chloroplast genomes respectively were used for molecular phylogenetic analysis. Genetic diversity measures show low levels of genetic variation within and high differentiation between populations, an indication of very low levels of gene flow. Populations of the <i>B. dregei</i> complex appeared as a monophyletic group. However, apart from some exceptions, relationships within the complex still remain largely unresolved with both sequence and combined data analysis. The analysis of diverse data sets produced results with many implications ranging from the impact of limited gene flow consistent with poor dispersal mechanisms to ancient hybridization probably brought about by interglaciation periods, when there was more rainfall and forests would have been more widespread bringing some populations into contact. An interplay between natural hybridization and the pervasive effects of micro-evolutionary processes such as random genetic drift (in small population sizes) has been proposed to explain the patterns of genetic and morphological variation in the complex. The ability of the populations of the <i>B. dregei</i> complex to interbreed and hybridize (a requirement for most species concepts) does not permit the populations of the <i>B. dregei</i> complex to be recognized as separate species but instead as highly divergent populations Conversely, considering modes of speciation, the sympatric speciation model supported the argument that local speciation is the rule rather than an exception in small effective population sizes and low levels of gene flow. en
dc.language English en
dc.title Evolutionary genetics of the Begonia dregei Complex (Begoniaceae) en
dc.type Doctoral degree en
dc.description.degree PhD en

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