Biogeography of Isolepis subgenus Fluitantes (C.B. Clarke), Muasya (Cyperaceae): niche conservatism, long distance dispersal and hybridization
Bachelor Thesis
2010
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University of Cape Town
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Numerous lineages of the Western Cape of South Africa show affinities with the flora of tropical Africa and with Australasia. Recent work suggests that most migrations between the Western Cape and tropical Africa occur in a northward direction, and that connections between the flora of regions in the Southern Hemisphere are maintained by wind-assisted long-distance dispersal. The Fluitantes clade of lsolepis (Cyperaceae: Cypereae) is distributed throughout these areas and provides a useful study group to assess the general validity of published biogeographical trends. Furthermore, the cooccurrence of several closely related species in the Cape floristic region allows geographical and ecological patterns to be used for inference of speciation processes in the clade. Sequence data of the ITS and atpi-H gene regions were collected for 82 specimens; these were used to construct haplotype networks and phylogenies. By using the Tristan da Cunha endemics in the genus, as well as results from higher-level studies, a dated phylogeny for the Fluitantes clade was constructed and allowed for ancestral character state optimization of distributions by maximum likelihood. Ecological data were extracted from geographic information systems map to test for environmental differentiation in the Cape taxa. The Fluitantes were found to have originated in the Cape 7 million years ago. From there, they spread east and northwards onto the mountains of East Africa and to the islands of the Indian Ocean. Multiple dispersal events to Australia were recorded. Incongruence between the plastid and nuclear gene trees indicate hybridization to have taken place in Australasia, with possible subsequent speciation. Although the multivariate analysis found some ecological differentiation between the three Cape species, there was substantial overlap in all variables, and interpretation of habitat differences was difficult. It is suggested that, instead, differentiation may have taken place at the microhabitat scale, as I. rubicunda occupies low-lying sandy depressions, I. striata occurs at higher altitudes floating in water, and I. Judwigii inhabits the edges of streams and wetlands.
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Viljoen, J. 2010. Biogeography of Isolepis subgenus Fluitantes (C.B. Clarke), Muasya (Cyperaceae): niche conservatism, long distance dispersal and hybridization. University of Cape Town.