Theses and Dissertations
http://hdl.handle.net/11602/2144
2024-03-28T08:48:52ZThe phenological study of Securidaca longepedunculata, in the Nylsvley Nature Reserve, Limpopo Province, South Africa
http://hdl.handle.net/11602/2636
The phenological study of Securidaca longepedunculata, in the Nylsvley Nature Reserve, Limpopo Province, South Africa
Mukhithi, Aluwani Godfrey
Phenological observations were conducted through analysis of phenological phases and stages of 200 sampled S. longepedunculata plant individuals in the sandy soil areas of Nylsvley Nature Reserve, Limpopo Province, South Africa. Phenological stages comprised of onset, peak development and decline; while phenological phase is time spent by those stages for example leaf yellowing (Ruml and Vulic, 2005). Phenological phases patterns were analysed by focussing on vegetative and reproductive phenophases. Vegetative phenophase considered the presence of budding and developmental stages of leaves until they are shed. Reproductive phenophase considered the presence of flowering and developmental stages of fruits until they are shed. Phenological data was mainly collected through direct ground based observation. The results showed that budding, leaf greening and flowering were observed from mid spring in September in response to upcoming summer which is warmer and rainy. Ripe seeds and leaf yellowing were predominantly visible in autumn and winter respectively, as they are in their annual maturity stage. Leaf and seed shedding were observed at their peak development from late winter in June to early spring in August, probably due to the effect of windy conditions on site. Changes in the phenology of S. longepedunculata plant individuals caused by environmental changes resulted in changes at the community level. This shows that thorough phenological pattern monitoring is essential in order to forecast plant species behaviour. Also, it is necessary to provide knowledge on proper management of the reserve and protection of the plant species.
MSc (Botany); Department of Biological Sciences
2023-10-05T00:00:00ZThermal biology of the two-spotted stink bug, Bathycoelia distincta (Hemiptera: Pentatomidae) a major pest of macadamia
http://hdl.handle.net/11602/2555
Thermal biology of the two-spotted stink bug, Bathycoelia distincta (Hemiptera: Pentatomidae) a major pest of macadamia
Muluvhahothe, Mulalo Meriam
The physiological functions of insects are mainly dictated by temperature because they rely on the
external environment to regulate their body temperatures. This temperature dependence drives their
performance, with profound implications on abundance and distribution. Daily environmental
temperature fluctuations may outpace an insect’s thermal tolerance capacity, which requires
physiological plastic mechanisms to survive. In the context of global warming, insects may be vulnerable
to temperature variations, and may ultimately determine their population dynamics. The two-spotted
stink bug, Bathycoelia distincta (Distant) (Hemiptera: Pentatomidae) is an important pest of macadamia
in South Africa. It causes damage by direct feeding on the kernel and comprises more than 80 % of the
shield bugs in the orchards. Increased crop losses due to stink bug damage threaten macadamia nut
production. Modern pest management practices require an understanding of the biology of pests and
ecology. An important question to pose is, how does an organism's thermal plastic traits affect its
ecological population dynamics? First, this study aimed to quantify the effects of temperature on
biological parameters of B. distincta life stages, such as the development rate, development duration,
survival, adult longevity, pre-oviposition period, oviposition period, and life table parameters, to
determine its thermal requirements and population growth at constant temperatures ranging from 19 to
29 °C. In addition, the effect of diet (macadamia nut and sweetcorn) on development, survival, and sex
ratio was investigated at 25 °C (Chapter 2). Second, to quantify the phenotypic plasticity of B. distincta life
stages. Two thermal tolerance indices were explored: rapid hardening (rapid heat hardening: RHH and
cold hardening: RCH) and acclimation (critical thermal maximum: CTmax and minimum: CTmin). RHH and
RCH were determined by exposing B. distincta life stages to extreme temperatures of 41 and -8 °C,
respectively. Acclimation effects on CTmax and CTmin were quantified by exposing B. distincta life stages to
48 h at 20, 25, and 30 °C. Temperature was ramped up and down at a rate of 0.2 min-1 to score survival at
high (CTmax) and low (CTmin) critical temperature points (Chapter 3). Thirdly, the development rate was
monitored (on the host plant) at temperatures ranging from 18 to 40 °C to acquire the total heat required
to complete development (degree-days) and thermal requirements of each life stage of B. distincta.
iv
Lastly, the physiological traits, degree-days, and thermal requirements were used to predict seasonal
generation turn-over, heat and cold thermal stress, thermal safety margin (TSM), and relative fitness in
macadamia orchards along an elevational gradient (705 - 1493 m a.s.l.) to determine the effects of climatic
zones (Cwa climate zone: Monsoon-influenced humid subtropical climate, Cwb: Subtropical highland
climate or Monsoon-influenced temperate oceanic climate, and Bsh: Hot semi-arid steppe climate)
(Chapter 4). B. distincta developed at a wide range of temperatures on sweetcorn (18 to 29 °C) and
macadamia nut (18 to 35 °C). The survival rate was high (51 to 100 %) between temperatures with a
monotonic increase of population growth from 19 to 29 °C. The total number of heat units required to
complete development was 783 DD. All life stages of B. distincta displayed thermal plasticity, but instar 2
was the most plastic stage except in response to cold acclimation. Response to extremes varied more at
low extreme temperatures compared to high extremes. As expected, the number of generations
decreased with increasing elevations from the Cwa (Arbor: 2.4 generations) to the Cwb climate zone
(Highfield: 1.1 generations). None of the life stages experienced thermal stress. TSM and relative fitness
were highest at the Cwb climate zone of the highest elevation. These findings suggest that B. distincta will
potentially cause more damage in response to global warming because of its estimated population growth
rate at elevated temperatures. Although relative fitness was highest in the Cwb climate zone, damage
could be expected in the Cwa zone due to increased number of generations. This study can also help
identify macadamia orchards in climate zones vulnerable to climate-related consequences such as
outbreaks. Climatic data combined with the DD model can be used to predict the phenology of B. distincta
and timing of chemical applications. The impacts of global warming on crop losses due to insect pests are
evident worldwide, and this study has shown that macadamia orchards in certain climatic zones (e.g., Cwa
climate zone) could be at risk of increased abundance of B. distincta. Thus, integrated pest management
strategies should be of priority to macadamia farmers for effective management of B. distincta. Given that
South Africa is the largest producer of macadamia globally and its major pest is thermal plastic, linking the
physiological traits of B. distincta life stages to climatic conditions of all macadamia growing regions in
South Africa will help understand its distribution limits.
PhD (Zoology); Department of Biological Sciences
2023-10-05T00:00:00ZAn inventory, nutritional analysis and biological evaluation of underutilized indigenous vegetables used to manage non-communicable diseases in Thulamela local municipality, Vhembe District Municipality, South Africa
http://hdl.handle.net/11602/2362
An inventory, nutritional analysis and biological evaluation of underutilized indigenous vegetables used to manage non-communicable diseases in Thulamela local municipality, Vhembe District Municipality, South Africa
Phaswane, Mukhethwa Concila
Non-communicable diseases have emerged as a serious public health concern around the world, with a high death rate. The study aim was to document and evaluate the biological activities of underutilized indigenous vegetables used by local people in Thulamela Local Municipality to manage non-communicable diseases. An open structured interview was used to conduct an ethnobotanical survey, and 25 underutilized indigenous vegetables belonging to 13 families were documented. Cucurbitaceae was the dominant family, constituting 21% of the documented species, followed by Urticaceae with 13% of the species. Six of the documented species, which are Citrullus colocynthis, Cleome gynandra, Cucumis africanus, Oxygonum dregeanum, Pouzolzia mixta, and Sonchus oleraceus, were selected and evaluated using standard laboratory procedures for quantifying nutritional, phytochemical constituents, antioxidant, and anti-diabetic activities.
The above-mentioned six vegetables contained a considerable amount of important nutrients. Cucumis africanus has the highest levels of ascorbic acid, Ca, Fe, and Mg. In comparison to other vegetables studied, Citrullus colocynthis had the highest levels of total phenolics, total flavonoids, and condensed tannins. The free radical-scavenging activity of all the plant extracts was moderate compared to the positive control (ascorbic acid). On the other hand, dichloromethane and acetone extracts exhibited high antioxidant activity in the beta-carotene-linoleic acid antioxidant system. Most dichloromethane, acetone and distilled water extracts showed low alpha-glucosidase inhibition compared to the positive control (acarbose). However, the dichloromethane extract of Citrullus colocynthis and acetone extract of Cucumis africanus exhibited significantly high alpha-glucosidase inhibitory activity than acarbose.
According to the information gathered, people in Thulamela Local Municipality rely on indigenous vegetables for medicine to treat non-communicable diseases. The quantified nutritional and phytochemical contents and the antioxidant and alpha-glucosidase inhibitory activities exhibited by the selected underutilized indigenous vegetables confirm their traditional uses as food and medicine to manage diabetes and other non-communicable diseases. To obtain precise data that can be used to verify these findings, in vivo methods should be used.
MSc (Botany); Department of Biological Sciences
2022-11-10T00:00:00ZGenomic mechanisms underpinning phenotypic diversity in the spiral-horned antelopes (Genus: Tragelaphus)
http://hdl.handle.net/11602/2355
Genomic mechanisms underpinning phenotypic diversity in the spiral-horned antelopes (Genus: Tragelaphus)
Rambuda, Thabelo
The world is old, full of diversity, and the history of all organisms that once lived on Earth is recorded in the DNA of its descendants. The genomes of living organisms contain ancestral information that, if analyzed, reveals the underlying mechanisms to explain an organism’s evolutionary history. Therefore, it is crucial to study the whole genomes of highly diverse and specialized groups of organisms that could help our understanding of the speciation process. The continent of Africa is home to phenotypically diverse spiral-horned antelopes (genus Tragelaphus) which have gone through a recent adaptive radiation. Previous studies on Tragelaphus have argued that they comprise either nine or ten species based on mtDNA and nuclear DNA respectively/chromosomal number difference. With the same mentioned molecular data, there is discordance in their previously reconstructed species tree, placing species in different clades with different markers. At the mtDNA level, the nyala (T. angasi) is sister to the bushbuck (T. scriptus) making the mtDNA diversity polyphyletic within the bushbuck complex. The two bushbuck species and other phenotypically similar non-sister Tragelaphus lineages lead to the suggestion by scientists that some phenotypes evolved through convergent evolution. In this study, one whole genome of each Tragelaphus lineage was sampled with the aim to analyze the genome-wide relationship of these species by reconstructing their phylogenetic species tree. The study also aims to assess the genome-wide levels of diversity and to assess whether there has been gene flow between species which could have led to phylogenetic discordance among traditional markers. The relationship was analyzed with non-model based PCA and biological model-based IBS and maximum likelihood. All the methods used for structure analysis revealed the same genomic structure and confirmed other studies showing that morphologically similar Tragelaphus species were not most closely related at the genome level. The reconstructed genome-wide species tree was used for the assessment of introgression between species. Most of the observed gene flow was ancestral, the alleles of which are randomly kept in some lineages and passed from generation to generation but lost in others. Therefore, I propose that some phenotypic similarities between unrelated species could be due to high ancestral gene flow between these non-sister lineages. To confirm this would require further investigation using more samples for each species.
MSc (Zoology); Department of Biological Sciences
2022-11-10T00:00:00Z