Doctoral Degrees (Biochemistry)

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Browsing Doctoral Degrees (Biochemistry) by Author "Bytebier, Benny (Benny Leopold Germaine)"

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    Molecular phylogenetic relationships within the subtribe Disinae (Orchidaceae) and their taxonomic, phytogeographic and evolutionary implications
    (Stellenbosch : Stellenbosch University, 2007-03) Bytebier, Benny (Benny Leopold Germaine); Bellstedt, D. U.; Linder, H. Peter; Stellenbosch University. Faculty of Science. Dept. of Biochemistry.
    ENGLISH ABSTRACT: Twenty five years after the last major morphological revision, phylogenetic relationships were inferred on the basis of a new DNA dataset for the African orchid subtribe Disinae, which includes the large genus Disa and the small genus Schizodium. One nuclear gene region (ITS) and two plastid gene regions (trnLF and matK) were sequenced for 136 ingroup, representing 70% of all known Disinae species, as well as for 7 outgroup taxa. The combined data matrix contained 4094 characters and was analysed using parsimony and Bayesian inference. The generic status of Schizodium can no longer be supported, as it is deeply embedded within the genus Disa. Furthermore, the currently recognised subgenera do not reflect the phylogenetic relationships. Several of the currently recognised sections are monophyletic, others contain misplaced elements, while some are polyphyletic. These results necessitate a re-classification of the Disinae. A monotypic subtribe Disinae and a subdvision of Disa into eighteen sections is formally proposed. These sections are monophyletic, well-supported, morphologically distinguishable and are delimited to maximize the congruence with the previous classification. All currently known species are enumerated and assigned to sections. Likelihood optimisation onto a dated molecular phylogeny is subsequently used to explore the historical biogeography of Disa, as well as of three other Cape lineages (Irideae p.p., the Pentaschistis clade and Restionaceae), to find out where these lineages originated and how they spread through the Afrotemperate region. Three hypotheses have been proposed: (i) a tropical origin with a southward migration towards the Cape; (ii) a Cape origin with a northward migration into tropical Africa and (iii) vicariance. None of these hypotheses, however, has been thoroughly tested. In all cases, tropical taxa are nested within a predominantly Cape clade and there is unidirectional migration from the Cape into the Drakensberg and from there northwards into tropical Africa. Dating estimates show that the migration into tropical East Africa has occurred in the last 17 million years, consistent with the Mio-Pliocene formation of the mountains in this area. The same technique is then utilised to reconstruct the temporal occurrence of ancestral ecological attributes of the genus Disa. The first appearance of species in the grassland and savanna biomes, as well as in the subalpine habitat, are in agreement with the existing, reliable geological and paleontological information. This suggests that phylogenies can be used to date events for which other information is lacking or inconclusive, such as the age of the fynbos biome and the start of the winter rainfall regime in southern Africa. The results indicate that these are much older than what is currently accepted and date back to at least the Oligocene.