Masters Research – University of Cape Town
Environmental gradients and the evolution of hemiparasitism
The genus Thesium contains ~330 species, primarily distributed throughout the old world, with a large clade of species centered in the winter, ‘Cape’ region of South Africa. These semi-parasitic plants use their haustoria (modified root organs) to obtain nutrients and carbohydrates from the roots of the plants growing around them. This may be particularly advantageous when growing in nutrient poor environments, where access to essential nutrients is limiting to growth and reproduction. In my research, I found that species with more parasitic growth forms tend to occupy more nutrient poor environments, while, in a comparison between two species, greener, leafier species are less reliant on their hosts for Carbon. Correlative analyses using both raw and phylogenetically independent (PIC) data show that divergence within the clade of Cape Thesium in the degree of heterotrophy as measured using a series of traits, specifically leafiness, plant height and tissue chlorophyll and N content, reflects adaptation to edaphic environments which vary in terms of their nutritional properties. The fact that the radiation in Cape Thesium has been accompanied by morphological shifts, which are consistently associated with shifts to different environments, suggests that diversification in Thesium has been adaptive. Edaphic heterogeneity in the CFR has played a significant role in driving the morphological and taxonomic diversification of Cape Thesium. Parasitism in Thesium may thus represent a specialized foraging strategy for overcoming deficiencies in available nutrients in the nutrient poor environments of the CFR. The first part of my dissertation has been published.