Nested clade analysis of geographic structure in the morphologically variable Themeda triandra in South Africa
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University of Cape Town
The use of phylogeography in plant systems has been on the increase in recent years with the use of chloroplast DNA to detect sufficient intraspecific variation to reach significant conclusions about plant species histories, both temporally and spatially. In this study, the geographic structure and possible origin of the morphologically variable Themeda triandra is explored. The trnF - trnC and psbD - trnS gene regions of the cpDNA were used to find 12 haplotypes found in 11 populations of T. triandra that encompass the species large distributional range. A haplotype tree was constructed that showed the relationship of the 11 haplotypes (haplotype_H12 was excluded as it fell outside of the 95% confidence limit), with haplotype H6 inferred to be the ancestral haplotype. A nested clade analysis was performed with the results used to infer the geographic structure of T. triandra within South Africa. Significant results showed that there was restricted gene flow with nested clades involving the three Free State populations, indicating that there are barriers to gene flow with other haplotypes. The ancestral haplotype showed long distance colonisation, with a probable root of this colonisation being the Kruger National Park. This is the proposed point of introduction of T. triandra into South Africa, with results from this study supporting this proposal. A substantial amount of gene flow (25.49%; AMOV A) between populations is observed, with this probably being due to the widespread distribution of haplotypes H6 and H10. It is thought that T. triandra followed two migration routes within South Africa: one along the coast, with the other inland above the escarpment where populations became genetically isolated from populations below the escarpment. Further studies may look for a correlation between morphological variants of T. triandra and the cpDNA haplotypes found within the species.
Oatley, G. 2004. Nested clade analysis of geographic structure in the morphologically variable Themeda triandra in South Africa. University of Cape Town.