Gazania is a small genus of the subtribe Gorteriinae, tribe Arctoteae, that is endemic to southern Africa. The genus was last revised in 1959 by Roessler, who noted that delimitation of the species of Gazania can be “extraordinarily difficult”. Morphometric data was collected to test the reality of the 16 species as delimited by Roessler, who based species boundaries on morphological characters. Only six taxa were found to be morphologically distinct, while the remaining samples showed no species cohesion. DNA sequence data from two nuclear spacer regions (ITS and ETS) and four chloroplast noncoding regions (the trnL and rpS16 introns, and the psbA-trnH and trnL-F spacers) of 43 samples were utilised to create a species level phylogeny and to investigate correlations between genetically delimited units and morphologically defined taxa. DNA sequence data reveal that seven species (as delimited by Roessler) are morphologically and genetically distinct. The remaining nine of Roessler’s species fall into a morphologically and genetically overlapping continuum that forms an ochlospecies. Phylogeographic methods (based on an expanded ITS and ETS DNA sequence data set from 169 samples) were employed to further resolve the limits of species, with special focus on the clades within the ochlospecies. These genetically defined clades were correlated with their geographical distributions, and in combination with molecular dating techniques, used to elucidate the recent climatic or environmental factors that may have shaped the phylogeographic structure of the genus. Phylogeographic patterns and molecular dating reveals that the genus Gazania is an example of a South African endemic clade that has undergone episodic cladogenesis in response to fluctuating climatic conditions over the last seven million years. The ochlospecies within Gazania is a result of repeated cycles of climate driven isolation in refugia and subsequent expansion and hybridization events during the Pliocene and Pleistocene. Comparisons with phylogeographic studies on other organisms reveal a common pattern indicative of the presence and evolutionary importance of an ancestral refugium in the arid Richtersveld / Namib region of southern Africa.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Botany))--University of Pretoria, 2005. / Plant Science / unrestricted

In Africa, non-communicable diseases such as diabetes mellitus have been generally neglected. This problem has worsened over the years owing to continuous threats from infectious diseases such as HIV/AIDS, tuberculosis and malaria. Despite this, statistics have shown that by 2030, the African region will have the highest proportional increase in diabetes prevalence. Over 80% of all diabetic deaths occur in developing countries probably not only due to poor equity of access to medication but also due to limited efficacy and side effects associated with the commonly available anti-diabetic agents. Therefore, this creates the desperate need for the development of new anti-diabetic agents that are more efficacious and can be sourced from within the continent. With oxidative stress as a suggested mechanism underlying the cause of diabetes mellitus and diabetic complications, the discovery of natural anti-oxidants that prevent free radical mediated damage is important for developing new treatment strategies. Marine algae have been identified as good sources for natural anti-oxidants. Unfortunately, very few studies have embarked on the discovery of marine-derived anti-oxidant compounds with potential anti-diabetic activity. In this project, we investigated the potential anti-oxidant activity of the South African endemic algae Stypopodium multipartitum, Dictyopterus ligulata, Cystophora fibriosa, Bifurcariopsis capensis, Sargassum sp. and Sargassum heterophyllum. From these studies, Sargassum heterophyllum yielded prenylated compounds, the main compound being sargahydroquinoic acid (3.6) and the carotenoid metabolite fucoxanthin (3.8), which are in part responsible for the radical scavenging activity of the crude extract. Sargahydroquinoic acid (3.6) and fucoxanthin (3.8) also exhibited significant anti-inflammatory activity. Sargaquinoic acid (3.1), sargachromenoic acid (3.9) and sarganaphthoquinoic acid (3.10) were then semi-synthesized from sargahydroquinoic acid (3.6) and their in-vitro cytotoxicity profiles evaluated using Chang Liver, HT-29, Caco-2 and 3T3-L1 cell lines prior to antidiabetic testing. From the semi-synthetic derivatives, sargachromenoic acid (3.9) exhibited the most potent anti-oxidant activity (IC₅₀ = 6.99 μg/mL). After the evaluation of antidiabetic activity using 3T3-L1 preadipocyte differentiation, sarganaphthoquinoic acid (3.10) showed the most potent insulinomimetic activity at 1.19 μM by inducing a PPARγ response similar to that of rosiglitazone at 1 μM.

Please read the abstract in the section 00front of this document / Dissertation (MInst Agrar (Plant Protection))--University of Pretoria, 2005. / Microbiology and Plant Pathology / unrestricted

It is generally assumed that when natural habitat is converted to human-dominated cover such area is “lost” to its native species. Extinctions will ensue. The literature generally assumes that species are extirpated as natural area is reduced, following the well-known species-area relationship (SAR). However, SARs have consistently over-estimated species losses resulting from conversion of natural habitat to human-dominated land covers. We hypothesize that the overestimation occurs because these area-based models assume that converted habitat is “lost”, eliminating all species. However, in the real world, conversion of natural land cover to human-dominated cover frequently produces new land covers, different from the original habitat, but not necessarily completely inhospitable to biodiversity. We evaluated the responses of total avian richness, forest bird richness and open habitat bird richness to remaining natural area within 991 quadrats, each 100 km2, across southern Ontario. Total bird species richness does not follow SAR predictions; rather, the number of bird species peaks at roughly 50% natural land cover. The richness of forest birds does follow the usual SAR power-law as a function of forested area. In contrast, richness of birds that prefer open-habitat does not increase monotonically with either natural- or human-dominated land cover. However, we can partition human-dominated land cover into an “available human-dominated” component and “lost” habitat. Richness of open-habitat species relates to the amount of available human-dominated cover. Distinguishing three habitat types (natural, available human-dominated, and lost) permits accurate predictions of species losses in response to natural habitat conversion.

Please read the abstract in the section 00front of this document / Dissertation (MSc (Pharmacology))--University of Pretoria, 2007. / Pharmacology / unrestricted

Please read the abstract in the section 00front of this document / Dissertation (MSc (Botany))--University of Pretoria, 2003. / Plant Science / unrestricted

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The Tushar Mountains of Utah provide essential alpine habitat to a variety of flora and fauna, including 27 endemic plant species and several ungulates (mountain goats, deer, elk, cattle). These ungulates were observed throughout two growing seasons and field analyses were conducted to assess foraging selection. Overall, most ungulates, especially large nursery herds, tended to prefer foraging amongst alpine regions within the Bullion volcanic of the Tushars, which is characterized by denser vegetation than the Belknap volcanic region. Mountain goats and deer were most frequently observed foraging within the Tushar alpine habitat; however, elk and domestic cattle were also observed. Mountain goats preferred foraging at higher elevations than other ungulates and shared the most dietary overlap with deer. Out of the 27 plant species endemic to this region, only Castilleja parvula var. parvula, commonly known as the Tushar paintbrush, was encountered frequently utilized by ungulates. This plant species was also observed being eaten by a variety of rodents and lagomorphs. Long-term monitoring plots were established in four different populations of C. parvula var. parvula across the Bullion volcanic range of the Tushars. These plots were revisited on a yearly basis and used to ascertain demographic data, which will shed light on population trends over time. A variety of different measurements were used to better understand the biology and habitat requirements of this rare plant species. Although the four monitored populations share many similarities, they each have their own site characteristics, local densities, relative plant communities, and potential threats. Further monitoring is necessary to better understand trends and assess the level of the various threats to C. parvula var. parvula populations.

Reproductive barriers are vital to generating new species as well as maintaining distinct species. Investigating reproductive barriers between closely related plant taxa helps us to understand how these barriers are maintained, particularly between rare and widespread relatives. Layia jonesii, a rare San Luis Obispo County serpentine endemic, and L. platyglossa, a common coastal species, co-occur on serpentine derived hillsides and are interfertile. At these locations, L. jonesii is isolated to dry soils near serpentine rock outcrops and L. platyglossa is located on slightly deeper grassland soils surrounding the rock outcrops. On hillsides where they co-occur, I observe two morphologically distinct species, therefore the two species must be maintaining reproductive barriers, yet mechanisms that maintain this isolation are unknown. I studied this system to investigate possible mechanisms contributing to the maintenance of reproductive barriers. I hypothesize prezygotic reproductive isolation in this system is due to (1) habitat isolation due to local adaptation to differential edaphic environments on the hillside, (2) flowering time differences, and (3) reduced seed set resulting from hybrid crosses. To investigate the local adaptation of L. jonesii and L. platyglossa, I reciprocally transplanted both species into the center of each species’ distribution. I also conducted a competition experiment to determine if L. jonesii is sensitive to resource competition beyond its natural distribution. To investigate flowering time differences, I tracked flowering time of both wild and reciprocally transplanted populations. I also performed controlled crosses to determine if heterospecific, or hybrid crosses, result in lowered seed set than conspecific crosses. The reciprocal transplants showed L. platyglossa is locally adapted to the grassland habitat. Local adaptation likely prevents L. playtyglossa from dispersing into the rock outcrop habitat. Results of the competition experiment revealed L. jonesii is sensitive to competition and this may contribute to its constrained distribution to shallow soils. Local adaptation and competition likely contribute to habitat isolation between the two species. I also documented stark differences in flowering time between the species which contributes to reproductive isolation by reducing pollen flow. Hybrid crosses also resulted in lowered seed set than conspecific crosses. These results suggest prezygotic barriers to reproduction likely maintain the majority of isolation between the two species. These results provide insight into mechanisms that maintain reproductive barriers between closely related taxa existing in similar habitats. The results also contribute to our understanding of how rare plants preserve genetic integrity near common and interfertile relatives.