A multidisciplinary study to assess the ecology of the Cape sea urchin, Parechinus angulosus, and its emerging use as a bioindicator to monitor coastal resiliency
- Authors: Redelinghuys, Suzanne
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435691 , vital:73179 , DOI 10.21504/10962/435692
- Description: The resilience of marine species in the face of unpredictable climate change stands as a paramount concern for the maintenance of ecological stability. Under such fluctuating conditions, it is critical to understand how organisms mitigate these effects in physiological, genetic, and morphological terms. To that end, this thesis focused on the Cape sea urchin, Parechinus angulosus, employing a multidisciplinary approach encompassing morphology, genomics, and gut microbial diversity to assess its potential as a bioindicator species and elucidate its adaptive strategies in response to varying environmental conditions along the South African coastline. This was achieved through studying their anatomy in order to link observed variation to prevailing local environmental conditions, aided by the species’ wide distribution range which allows insight into adaptations across broad geographic regions and ecological settings. The first empirical chapter, Chapter 3, focusing on eight key morphometric traits of test, Aristotle’s lantern and spines, revealed distinct variation in the Cape sea urchin's morphology between the east and west coasts of South Africa, suggesting the presence of some level of local adaptation to the prevailing environmental factors found on the east and west coasts of South Africa. This points to potential bioindicator capabilities of the species, reflecting adaptive divergence amidst contrasting environmental conditions. Further analysis is however necessary in order to isolate specific physiological trends that may be associated with these morphometric differences, thereby enhancing and tightening their ecological implications. The second experimental chapter, Chapter 4, delved into the genetic structure of the Cape urchin by investigating genome-wide diversity, the presence of cryptic population structure, and spatial patterns of genomic diversity. Moderate genomic differentiation was detected among populations along the eastern and western coasts of South Africa by outlier loci that may undergo natural selection, which could indicate local adaptation to environmental conditions. This pattern hints at adaptive differentiation and cryptic genetic structures within the Cape sea urchin populations and emphasises the species' potential adaptive responses to localised (in this case regional) environmental pressures. Assigning functional significance to these genetic variations will require a comprehensive annotated reference genome, a limitation acknowledged in the current study. Chapter 5 explored the gut microbial diversity and revealed significant compositional variations between the east and west coast populations of South Africa, confirming regional and inter-regional variation. This chapter also highlighted the essential biochemical pathways critical to the survival of the host which is crucial for assessing the health of the urchin host. Together, the functional content of the gut bacteria and microbial diversity showcases its potential as a bioindicator for coastal ecosystem health. Logistical challenges and confounding factors like host physiology will need to be fully considered for its effective application. Overall, the findings of this doctoral research suggest that the Cape sea urchin displays promising characteristics as a bioindicator species due to its morphological, genetic, and gut microbial variations in response to environmental differences, providing a diverse array of means in which urchins could be used as bioindicators, from their uses to assess water quality and detect pollution, to ecosystem health monitoring and biodiversity studies in which sea urchin abundance, distribution, and presence are monitored. Further research, integrating these multidisciplinary approaches is recommended to validate and refine its bioindicator potential. Additionally, the development of a comprehensive annotated reference genome is imperative to harness the species' genetic information effectively. This study underscores the significance of integrating multiple disciplines in understanding how species respond to environmental change and their potentials contributions to monitor ecological resilience. The original multidisciplinary approach, combined with high computational outputs presents a promising framework for a comprehensive ecological monitoring in marine ecosystems. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Authors: Redelinghuys, Suzanne
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435691 , vital:73179 , DOI 10.21504/10962/435692
- Description: The resilience of marine species in the face of unpredictable climate change stands as a paramount concern for the maintenance of ecological stability. Under such fluctuating conditions, it is critical to understand how organisms mitigate these effects in physiological, genetic, and morphological terms. To that end, this thesis focused on the Cape sea urchin, Parechinus angulosus, employing a multidisciplinary approach encompassing morphology, genomics, and gut microbial diversity to assess its potential as a bioindicator species and elucidate its adaptive strategies in response to varying environmental conditions along the South African coastline. This was achieved through studying their anatomy in order to link observed variation to prevailing local environmental conditions, aided by the species’ wide distribution range which allows insight into adaptations across broad geographic regions and ecological settings. The first empirical chapter, Chapter 3, focusing on eight key morphometric traits of test, Aristotle’s lantern and spines, revealed distinct variation in the Cape sea urchin's morphology between the east and west coasts of South Africa, suggesting the presence of some level of local adaptation to the prevailing environmental factors found on the east and west coasts of South Africa. This points to potential bioindicator capabilities of the species, reflecting adaptive divergence amidst contrasting environmental conditions. Further analysis is however necessary in order to isolate specific physiological trends that may be associated with these morphometric differences, thereby enhancing and tightening their ecological implications. The second experimental chapter, Chapter 4, delved into the genetic structure of the Cape urchin by investigating genome-wide diversity, the presence of cryptic population structure, and spatial patterns of genomic diversity. Moderate genomic differentiation was detected among populations along the eastern and western coasts of South Africa by outlier loci that may undergo natural selection, which could indicate local adaptation to environmental conditions. This pattern hints at adaptive differentiation and cryptic genetic structures within the Cape sea urchin populations and emphasises the species' potential adaptive responses to localised (in this case regional) environmental pressures. Assigning functional significance to these genetic variations will require a comprehensive annotated reference genome, a limitation acknowledged in the current study. Chapter 5 explored the gut microbial diversity and revealed significant compositional variations between the east and west coast populations of South Africa, confirming regional and inter-regional variation. This chapter also highlighted the essential biochemical pathways critical to the survival of the host which is crucial for assessing the health of the urchin host. Together, the functional content of the gut bacteria and microbial diversity showcases its potential as a bioindicator for coastal ecosystem health. Logistical challenges and confounding factors like host physiology will need to be fully considered for its effective application. Overall, the findings of this doctoral research suggest that the Cape sea urchin displays promising characteristics as a bioindicator species due to its morphological, genetic, and gut microbial variations in response to environmental differences, providing a diverse array of means in which urchins could be used as bioindicators, from their uses to assess water quality and detect pollution, to ecosystem health monitoring and biodiversity studies in which sea urchin abundance, distribution, and presence are monitored. Further research, integrating these multidisciplinary approaches is recommended to validate and refine its bioindicator potential. Additionally, the development of a comprehensive annotated reference genome is imperative to harness the species' genetic information effectively. This study underscores the significance of integrating multiple disciplines in understanding how species respond to environmental change and their potentials contributions to monitor ecological resilience. The original multidisciplinary approach, combined with high computational outputs presents a promising framework for a comprehensive ecological monitoring in marine ecosystems. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
Augmentation of Aphytis melinus DeBach (Hymenoptera: Aphelinidae) for the control of California red scale Aonidiella aurantii Maskell (Hemiptera: Diaspididae) on citrus
- De Beer, Ernst Friedrich Ludwig
- Authors: De Beer, Ernst Friedrich Ludwig
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435638 , vital:73175 , DOI 10.21504/10962/435638
- Description: Aphytis lingnanensis was reared and tested in South Africa in the early 2000s for augmentation against red scale on citrus and was found to be ineffective. Aphytis melinus is now commercially available and it is important that the efficacy of augmentation thereof on red scale is determined locally. Field trials, fitness assessments and molecular identification on A. melinus from two insectaries were done. Field trials was done in seven, five and six pairs of comparable release and control orchards across the Eastern and Western Cape during the seasons of 2019/2020, 2020/2021 and 2021/2022 respectively. Red scale infestation was monitored and a sample of 20 infested fruit from each orchard was randomly collected every four weeks. Aphytis spp. responsible for parasitism were identified and the percentage parasitism recorded. Results of this study of field trials suggest that the augmentation of A. melinus did not significantly increase the level of parasitism above that of the untreated control. Five repetitions with six replicates of flight and longevity tests were performed with wasps from each insectary. Wasps in the longevity test from two insectaries were kept at 23 °C and 65% RH with honey. Flight tests were performed in tubes of 16 by 30 cm, with a light above a clear, sticky ceiling at 23 °C and 65% RH. On average in five replicates, 65%, 33% and 17% A. melinus wasps were alive on day one, five and 10 respectively. The overall sex ratio was 1.58 for females to males, but 1.05, 2.19 and 2.66 for non-flyers, non-crawlers, crawlers, and flyers respectively. In flight tests for both insectaries combined, only 36.97% of wasps could initiate flight in 24 h while 56.96% remained on the tube floor, and 6.05% attempted to crawl upwards. No significant differences in flight performance were recorded between the two insectaries. Wasps from the local insectary lived significantly longer during the longevity tests but were shorter in transit than wasps from the overseas insectary. COI genes were sequenced and compared against Genbank sequences using BLAST. Molecular identifications did not confirm morphological identifications for all species, indicating unexpected genetic complexity. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Authors: De Beer, Ernst Friedrich Ludwig
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435638 , vital:73175 , DOI 10.21504/10962/435638
- Description: Aphytis lingnanensis was reared and tested in South Africa in the early 2000s for augmentation against red scale on citrus and was found to be ineffective. Aphytis melinus is now commercially available and it is important that the efficacy of augmentation thereof on red scale is determined locally. Field trials, fitness assessments and molecular identification on A. melinus from two insectaries were done. Field trials was done in seven, five and six pairs of comparable release and control orchards across the Eastern and Western Cape during the seasons of 2019/2020, 2020/2021 and 2021/2022 respectively. Red scale infestation was monitored and a sample of 20 infested fruit from each orchard was randomly collected every four weeks. Aphytis spp. responsible for parasitism were identified and the percentage parasitism recorded. Results of this study of field trials suggest that the augmentation of A. melinus did not significantly increase the level of parasitism above that of the untreated control. Five repetitions with six replicates of flight and longevity tests were performed with wasps from each insectary. Wasps in the longevity test from two insectaries were kept at 23 °C and 65% RH with honey. Flight tests were performed in tubes of 16 by 30 cm, with a light above a clear, sticky ceiling at 23 °C and 65% RH. On average in five replicates, 65%, 33% and 17% A. melinus wasps were alive on day one, five and 10 respectively. The overall sex ratio was 1.58 for females to males, but 1.05, 2.19 and 2.66 for non-flyers, non-crawlers, crawlers, and flyers respectively. In flight tests for both insectaries combined, only 36.97% of wasps could initiate flight in 24 h while 56.96% remained on the tube floor, and 6.05% attempted to crawl upwards. No significant differences in flight performance were recorded between the two insectaries. Wasps from the local insectary lived significantly longer during the longevity tests but were shorter in transit than wasps from the overseas insectary. COI genes were sequenced and compared against Genbank sequences using BLAST. Molecular identifications did not confirm morphological identifications for all species, indicating unexpected genetic complexity. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
Investigating occupation as frame for planning and developing agricultural extension VET skills for climate resilience: cross-case analysis of Alice, South Africa, and Gulu, Uganda
- Authors: Muhangi, Sidney
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/436559 , vital:73282 , DOI 10.21504/10962/436559
- Description: In sub-Saharan Africa and most of the Global South, climate change is challenging work and livelihoods for smallholder farmers who depend on rainfed farming, demanding climate resilience. Smallholder agriculture in Africa remains a mainstay for most economies and livelihoods, including South Africa and Uganda. My firsthand experience in Uganda as a subsistence farmer revealed the vitality of extension services to farmers. Participating in VETAfrica 4.0, a VET skill planning project, sparked my interest in examining the adequacy of 'Occupation' as a skills planning tool for addressing contemporary climate change challenges faced by extension officers and farmers, with implications for skills development. This research sought to answer the question: What is the theoretical and practical history and current constitution of the agricultural extension officer occupation as a mediating unit of intervention for VET skills planning, and is it adequate for climate resilience? The study addressed five objectives. First, the study undertook a historical review of occupation as a mediating unit of intervention for skills planning. Secondly, the study examined current descriptions of the extension occupation as used for skills planning in Africa. Thirdly, in order to better understand the operationalisation of this skills planning instrument, the study examined aspects of skills development, specifically how VET preparation for extension work was taking place in response to the need for climate resilience through a curriculum review and the experiences and related work activities of extension services actors. The study also reviewed agricultural extension and VET policy, and labour market data for its responsiveness to climate resilience. In response to the findings of Objectives 1-4, a fifth objective was developed to offer expanded possibilities for a mediating unit of intervention for skills planning and development relevant to climate resilience in agricultural extension, as this appeared to be needed. To develop the study, I drew on the Social Ecosystems Model (SEM) for skills, which raises the issue of mediation in skills development. I also drew on Cultural-Historical Activity Theory (CHAT) to help theorise the mediation in the SEM for skills, where different activity systems (policy, training and extension, farming) were present. This framework allowed me to probe how these activity systems were mediating climate-resilient skills development with/for extension services (or not). Empirical data was produced through secondary and primary data, generated in two case study contexts using a cross-case design. Documentary analysis involved analysing policy documents, study curricula and historical literature to develop an understanding of historical sociology of occupation as a skills planning mediating unit and insight into contemporary understanding of how occupational frameworks are structured and deployed. Analysis was undertaken in two stages; firstly, through in-depth cases of occupation as mediating unit of intervention for skills planning, and aspects of skills development as influenced by this as influenced by this mediating unit (Chapter 5 and 6). This offered a first layer of analysis and insights into temporality, verticalities, mediation and horizontalities in the SEM for skills in each case. Secondly, abduction was undertaken to build models of the SEM for skills as found in each of the two countries using the SEM and CHAT analytical tools (Chapter 7), showing the need for skills planning tools that are more closely related to and relevant to the contexts of skills development. Findings revealed insights into the SEM for skills related to ecological time, notably a mismatch between the cultural-historical time of occupational skills planning and development, and the temporal demands for climate resilience. Historical analysis the deep rootedness of occupations and occupational structures in colonial histories and traditions, going back as far as the medieval era, with current occupations still bearing features of ancient occupational guild practices and hence not adequately responsive to climate change, affecting the SEM for skills in both cases and producing contradictions. Analysis further revealed that contemporary agricultural extension in Africa is decentralised and pluralistic, with few extension-related policies employed underdeveloped. Labour market in both South Africa and Uganda are not adequately orientated to climate resilience and fail to include climate resilience expertise, despite a need for this amongst farmers and by policy, revealing contradictions between various policy activity systems, which are not adequately facilitating. Empirical findings from study sites revealed that VET preparation for extension work lacks responsiveness to climate resilience within the skills ecosystem. Consequently, extension officers lack expertise in climate resilience, which is an increasing demand expressed by farmers and other horizontal activity systems in the SEM for skills. Through a more complex understanding of the extension officer occupation and its development in skills ecosystem in Africa, the study proposes a broader mediating unit of intervention for skills planning than that of ‘occupation’ only. The mediating unit of intervention put forward for skills planning is a workstream mapping approach for climate resilient extension training in VET. This planning approach has implications for skills development viewed as work, learning and living involving more than one activity system in the skills development landscape, thus also broadening the approach to VET. The study concludes with recommendations to further test this approach. Finally, it makes recommendations that can inform: 1) curriculum innovation, 2) extension practice, 3) policy, and 4) research. , Thesis (PhD) -- Faculty of Education, Secondary and Post School Education, 2024
- Full Text:
- Authors: Muhangi, Sidney
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/436559 , vital:73282 , DOI 10.21504/10962/436559
- Description: In sub-Saharan Africa and most of the Global South, climate change is challenging work and livelihoods for smallholder farmers who depend on rainfed farming, demanding climate resilience. Smallholder agriculture in Africa remains a mainstay for most economies and livelihoods, including South Africa and Uganda. My firsthand experience in Uganda as a subsistence farmer revealed the vitality of extension services to farmers. Participating in VETAfrica 4.0, a VET skill planning project, sparked my interest in examining the adequacy of 'Occupation' as a skills planning tool for addressing contemporary climate change challenges faced by extension officers and farmers, with implications for skills development. This research sought to answer the question: What is the theoretical and practical history and current constitution of the agricultural extension officer occupation as a mediating unit of intervention for VET skills planning, and is it adequate for climate resilience? The study addressed five objectives. First, the study undertook a historical review of occupation as a mediating unit of intervention for skills planning. Secondly, the study examined current descriptions of the extension occupation as used for skills planning in Africa. Thirdly, in order to better understand the operationalisation of this skills planning instrument, the study examined aspects of skills development, specifically how VET preparation for extension work was taking place in response to the need for climate resilience through a curriculum review and the experiences and related work activities of extension services actors. The study also reviewed agricultural extension and VET policy, and labour market data for its responsiveness to climate resilience. In response to the findings of Objectives 1-4, a fifth objective was developed to offer expanded possibilities for a mediating unit of intervention for skills planning and development relevant to climate resilience in agricultural extension, as this appeared to be needed. To develop the study, I drew on the Social Ecosystems Model (SEM) for skills, which raises the issue of mediation in skills development. I also drew on Cultural-Historical Activity Theory (CHAT) to help theorise the mediation in the SEM for skills, where different activity systems (policy, training and extension, farming) were present. This framework allowed me to probe how these activity systems were mediating climate-resilient skills development with/for extension services (or not). Empirical data was produced through secondary and primary data, generated in two case study contexts using a cross-case design. Documentary analysis involved analysing policy documents, study curricula and historical literature to develop an understanding of historical sociology of occupation as a skills planning mediating unit and insight into contemporary understanding of how occupational frameworks are structured and deployed. Analysis was undertaken in two stages; firstly, through in-depth cases of occupation as mediating unit of intervention for skills planning, and aspects of skills development as influenced by this as influenced by this mediating unit (Chapter 5 and 6). This offered a first layer of analysis and insights into temporality, verticalities, mediation and horizontalities in the SEM for skills in each case. Secondly, abduction was undertaken to build models of the SEM for skills as found in each of the two countries using the SEM and CHAT analytical tools (Chapter 7), showing the need for skills planning tools that are more closely related to and relevant to the contexts of skills development. Findings revealed insights into the SEM for skills related to ecological time, notably a mismatch between the cultural-historical time of occupational skills planning and development, and the temporal demands for climate resilience. Historical analysis the deep rootedness of occupations and occupational structures in colonial histories and traditions, going back as far as the medieval era, with current occupations still bearing features of ancient occupational guild practices and hence not adequately responsive to climate change, affecting the SEM for skills in both cases and producing contradictions. Analysis further revealed that contemporary agricultural extension in Africa is decentralised and pluralistic, with few extension-related policies employed underdeveloped. Labour market in both South Africa and Uganda are not adequately orientated to climate resilience and fail to include climate resilience expertise, despite a need for this amongst farmers and by policy, revealing contradictions between various policy activity systems, which are not adequately facilitating. Empirical findings from study sites revealed that VET preparation for extension work lacks responsiveness to climate resilience within the skills ecosystem. Consequently, extension officers lack expertise in climate resilience, which is an increasing demand expressed by farmers and other horizontal activity systems in the SEM for skills. Through a more complex understanding of the extension officer occupation and its development in skills ecosystem in Africa, the study proposes a broader mediating unit of intervention for skills planning than that of ‘occupation’ only. The mediating unit of intervention put forward for skills planning is a workstream mapping approach for climate resilient extension training in VET. This planning approach has implications for skills development viewed as work, learning and living involving more than one activity system in the skills development landscape, thus also broadening the approach to VET. The study concludes with recommendations to further test this approach. Finally, it makes recommendations that can inform: 1) curriculum innovation, 2) extension practice, 3) policy, and 4) research. , Thesis (PhD) -- Faculty of Education, Secondary and Post School Education, 2024
- Full Text:
Phthalocyanine-based bio-functional conjugates: photodynamic therapy and photoantimicrobial chemotherapeutic efficacy evaluation in-vitro
- Authors: Magadla, Aviwe
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435918 , vital:73212 , DOI 10.21504/10962/435918
- Description: This thesis reports on the syntheses and characterisation of symmetrical and asymmetrical phthalocyanines (Pcs) with different ring substituents derived to form either cationic styryl pyridine, cationic styryl pyridine triphenylphosphonium (TPP+)-based, benzothiazole, cationic pyridyl-dihydrothiazole and other closely related groups. The starting Pc complex of the synthesised Pc derivatives was typically obtained through the cyclotetramerisation of a substituted phthalonitrile. Then, depending on the desired final complex, the desired complexes were synthesised through the Knoevenagel condensation, alkylation reaction, and Schiff base reaction. Furthermore, silica nanoparticles (SiNPs) were also used to encapsulate Pcs. Following aminopropyl triethoxysilane amino (APTES) functionalisation of the surface of the Pc@SiNPs-APTES, biomolecules such as gallic acid, folic acid, and ampicillin were covalently attached to the surface. Additionally, Pc@SiNPs-APTES is protonated with 1,3-propanesultone. The pair of synthesised asymmetric Pcs is attached to ciprofloxacin (CIP) via an amide bond. Different analytical methods were used to characterise the Pcs and their conjugates. The photophysics and photochemistry of the Pcs both by themselves and in their conjugate form when doped with SiNPs. The cationic Pcs were able to produce sufficient singlet oxygen on their own in most cases. This is explained by the Pcs greater solubility in water. Since singlet oxygen is produced from the triplet state, singlet oxygen quantum yield (Δ) values complement triplet quantum yield (T) values. Low Δ values could be attributed to ineffective energy transfer; screening effects may have prevented the excited triplet state of the Pcs from interacting with the ground state molecular oxygen, lowering the Δ values. In other instances, the Pcs' protection by the SiNPs could be credited with extending the triplet lifetime. The direct connection of Pcs with CIP increased the formation of T and Δ in ABSTRACT comparison to Pcs alone. Both in planktonic and biofilm form, the cationic Pcs and conjugates showed enhanced bacterial elimination. The Pcs and conjugates demonstrated significant activity in photodynamic therapy treatment (PDT) experiments at the tested doses. In both PDT and photodynamic antimicrobial chemotherapy (PACT) treatment, the cationic Pcs outperformed the neutral Pc in terms of biological activity. , Thesis (PhD) -- Faculty of Science, Chemistry, 2024
- Full Text:
- Authors: Magadla, Aviwe
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435918 , vital:73212 , DOI 10.21504/10962/435918
- Description: This thesis reports on the syntheses and characterisation of symmetrical and asymmetrical phthalocyanines (Pcs) with different ring substituents derived to form either cationic styryl pyridine, cationic styryl pyridine triphenylphosphonium (TPP+)-based, benzothiazole, cationic pyridyl-dihydrothiazole and other closely related groups. The starting Pc complex of the synthesised Pc derivatives was typically obtained through the cyclotetramerisation of a substituted phthalonitrile. Then, depending on the desired final complex, the desired complexes were synthesised through the Knoevenagel condensation, alkylation reaction, and Schiff base reaction. Furthermore, silica nanoparticles (SiNPs) were also used to encapsulate Pcs. Following aminopropyl triethoxysilane amino (APTES) functionalisation of the surface of the Pc@SiNPs-APTES, biomolecules such as gallic acid, folic acid, and ampicillin were covalently attached to the surface. Additionally, Pc@SiNPs-APTES is protonated with 1,3-propanesultone. The pair of synthesised asymmetric Pcs is attached to ciprofloxacin (CIP) via an amide bond. Different analytical methods were used to characterise the Pcs and their conjugates. The photophysics and photochemistry of the Pcs both by themselves and in their conjugate form when doped with SiNPs. The cationic Pcs were able to produce sufficient singlet oxygen on their own in most cases. This is explained by the Pcs greater solubility in water. Since singlet oxygen is produced from the triplet state, singlet oxygen quantum yield (Δ) values complement triplet quantum yield (T) values. Low Δ values could be attributed to ineffective energy transfer; screening effects may have prevented the excited triplet state of the Pcs from interacting with the ground state molecular oxygen, lowering the Δ values. In other instances, the Pcs' protection by the SiNPs could be credited with extending the triplet lifetime. The direct connection of Pcs with CIP increased the formation of T and Δ in ABSTRACT comparison to Pcs alone. Both in planktonic and biofilm form, the cationic Pcs and conjugates showed enhanced bacterial elimination. The Pcs and conjugates demonstrated significant activity in photodynamic therapy treatment (PDT) experiments at the tested doses. In both PDT and photodynamic antimicrobial chemotherapy (PACT) treatment, the cationic Pcs outperformed the neutral Pc in terms of biological activity. , Thesis (PhD) -- Faculty of Science, Chemistry, 2024
- Full Text:
Plankton and macroinvertebrate dynamics in the Khakhea–Bray transboundary aquifer region
- Mungenge, Chipo Perseverance
- Authors: Mungenge, Chipo Perseverance
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435674 , vital:73178 , DOI 10.21504/10962/435674
- Description: Temporary wetlands are prevalent in semi–arid and arid climates across the globe and harbour unique faunal assemblages that significantly contribute to regional aquatic biodiversity. This study aims to enhance our understanding of the ecological dynamics of temporary wetland ecosystems, focusing on plankton dynamics, large branchiopod diversity, trophic dynamics, water quality and the impacts of freshwater salinisation in temporary pans in the Khakhea Bray Transboundary aquifer region in the North west Province, South Africa. This body of work represents field, laboratory and writing components which span the period May 2021 to December 2023. The results from this study revealed seasonal patterns in plankton diversity with a winter peak in phytoplankton diversity dominated by Zygnematophyceae species, while Chlorophyceae were dominant in summer. Zooplankton diversity was high in summer as compared to winter, with both Rotifera and Copepoda dominant in both seasons. Six large branchiopod species were found in the region, and three of these were new distribution records for the North west Province, including the first record of Phallocryptus spinosa in the salt pan that was sampled in summer. Large branchiopod diversity was mainly influenced by water temperature and phosphorous in summer, while sediment sodium influenced the diversity in winter. The stable isotope analyses used to determine trophic dynamics in these temporary pans revealed that the food web had four trophic levels, with the top predators being the notonectids Anisops sp. The dominant consumers were predatory insects such as Sigara sp., Anisops sp., Lestes sp., Rhantus sp. and Cybister sp. adults and larvae, as well as detritivorous Tomopterna sp. tadpoles. High trophic niche overlaps were found between the notonectids and the dytiscids. These temporary pans are susceptible to anthropogenic impacts, and disturbed pans were found to have elevated pH, ammonium, phosphates and dissolved oxygen compared to the undisturbed pans. A strong positive relationship was observed between chl–a and temperature, pH, dissolved oxygen, phosphates and ammonium. Chlorophyll–a concentration increased as surface area and the distance from kraals, buildings and latrines decreased. Freshwater salinisation was found to cause notable shifts in abiotic factors and benthic phytoplankton communities, favouring the proliferation of saline–tolerant diatom species at the cost of more sensitive taxa. The study also revealed that in interaction with salinisation, time also exerted a notable influence on shaping the benthic phytoplankton community. Salinity levels of 2.5 ppt and above led to significant decreases in emergent taxa richness and abundance, with Spinicaudata and Ostracoda being the most sensitive taxa to high salinities. There was a limited effect on community hatching phenology dynamics from salinity. This suggests that the main impact of salinisation in these systems will be reductions in hatching success and, hence, reduced recruitment. The study highlights the vulnerability of temporary pan ecosystems to anthropogenic influences and the complexities of interactions of organisms and the environmental conditions in these systems. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Authors: Mungenge, Chipo Perseverance
- Date: 2024-04-05
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435674 , vital:73178 , DOI 10.21504/10962/435674
- Description: Temporary wetlands are prevalent in semi–arid and arid climates across the globe and harbour unique faunal assemblages that significantly contribute to regional aquatic biodiversity. This study aims to enhance our understanding of the ecological dynamics of temporary wetland ecosystems, focusing on plankton dynamics, large branchiopod diversity, trophic dynamics, water quality and the impacts of freshwater salinisation in temporary pans in the Khakhea Bray Transboundary aquifer region in the North west Province, South Africa. This body of work represents field, laboratory and writing components which span the period May 2021 to December 2023. The results from this study revealed seasonal patterns in plankton diversity with a winter peak in phytoplankton diversity dominated by Zygnematophyceae species, while Chlorophyceae were dominant in summer. Zooplankton diversity was high in summer as compared to winter, with both Rotifera and Copepoda dominant in both seasons. Six large branchiopod species were found in the region, and three of these were new distribution records for the North west Province, including the first record of Phallocryptus spinosa in the salt pan that was sampled in summer. Large branchiopod diversity was mainly influenced by water temperature and phosphorous in summer, while sediment sodium influenced the diversity in winter. The stable isotope analyses used to determine trophic dynamics in these temporary pans revealed that the food web had four trophic levels, with the top predators being the notonectids Anisops sp. The dominant consumers were predatory insects such as Sigara sp., Anisops sp., Lestes sp., Rhantus sp. and Cybister sp. adults and larvae, as well as detritivorous Tomopterna sp. tadpoles. High trophic niche overlaps were found between the notonectids and the dytiscids. These temporary pans are susceptible to anthropogenic impacts, and disturbed pans were found to have elevated pH, ammonium, phosphates and dissolved oxygen compared to the undisturbed pans. A strong positive relationship was observed between chl–a and temperature, pH, dissolved oxygen, phosphates and ammonium. Chlorophyll–a concentration increased as surface area and the distance from kraals, buildings and latrines decreased. Freshwater salinisation was found to cause notable shifts in abiotic factors and benthic phytoplankton communities, favouring the proliferation of saline–tolerant diatom species at the cost of more sensitive taxa. The study also revealed that in interaction with salinisation, time also exerted a notable influence on shaping the benthic phytoplankton community. Salinity levels of 2.5 ppt and above led to significant decreases in emergent taxa richness and abundance, with Spinicaudata and Ostracoda being the most sensitive taxa to high salinities. There was a limited effect on community hatching phenology dynamics from salinity. This suggests that the main impact of salinisation in these systems will be reductions in hatching success and, hence, reduced recruitment. The study highlights the vulnerability of temporary pan ecosystems to anthropogenic influences and the complexities of interactions of organisms and the environmental conditions in these systems. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
Case in modern standard Arabic
- Ghammaz, Hamzah Saleh Theyab
- Authors: Ghammaz, Hamzah Saleh Theyab
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435593 , vital:73171 , DOI 10.21504/10962/435593
- Description: This thesis provides a novel account of case checking in Modern Standard Arabic (henceforth MSA). It argues against the concept that nominative case in topic and comment structures is default. Default or inherent case is not related to case filter, nor is it assigned by any syntactic method. Some linguists claim that the default case in Arabic language is employed only when no case assigner is available. I argue, in light of the minimalist program (henceforth MP), that default (inherent) case is always a problem for syntactic theory and that the nominative case which the topic and comment sentences bear is valued by a functional head. The topic and comment constructions contain a predicational head (Pred)- a functional head, that is equivalent to vP which occurs in verbal constructions. The head of PredP is accountable for nominative case value on the topic and comment structures. This thesis also provides a novel paradigm regarding the clitics that appear at the end of verbs in MSA. This paradigm proves that these clitics are not agreement, tense, nor mood markers but rather Verbal Case markers and it provides a minimalist program account to explain case checking on verbs in MSA. Regarding sentence initial DP, and contra to the proposal that in SVO sentence initial DP is a subject, I have scrutinised the nature of this DP and provided enough evidence that it is a topic. Additionally, I have investigated the relationship between agreement asymmetry and the position of the subject in MSA from the minimalist feature inheritance account viewpoint. Mainly, I reviewed null pro hypothesis which proved to be redundant to account for the derivation of VSO or SVO word orders. I have also proved what were considered agreement markers are not agreement markers but resumptive pronouns. Finally, I proved that there is not agreement asymmetry in MSA. Agreement pattern in MSA results from the agree operation and it is achieved under Probe-Goal alignment; regardless of whether the Goal is raised up to Spec-TP or remains in situ (Spec-VP), the agreement is not supposed to change. This conclusion is in harmony with the principles of MP Agree Theory. , Thesis (PhD) -- Humanities, Linguistics and Applied Language Studies, 2024
- Full Text:
- Authors: Ghammaz, Hamzah Saleh Theyab
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/435593 , vital:73171 , DOI 10.21504/10962/435593
- Description: This thesis provides a novel account of case checking in Modern Standard Arabic (henceforth MSA). It argues against the concept that nominative case in topic and comment structures is default. Default or inherent case is not related to case filter, nor is it assigned by any syntactic method. Some linguists claim that the default case in Arabic language is employed only when no case assigner is available. I argue, in light of the minimalist program (henceforth MP), that default (inherent) case is always a problem for syntactic theory and that the nominative case which the topic and comment sentences bear is valued by a functional head. The topic and comment constructions contain a predicational head (Pred)- a functional head, that is equivalent to vP which occurs in verbal constructions. The head of PredP is accountable for nominative case value on the topic and comment structures. This thesis also provides a novel paradigm regarding the clitics that appear at the end of verbs in MSA. This paradigm proves that these clitics are not agreement, tense, nor mood markers but rather Verbal Case markers and it provides a minimalist program account to explain case checking on verbs in MSA. Regarding sentence initial DP, and contra to the proposal that in SVO sentence initial DP is a subject, I have scrutinised the nature of this DP and provided enough evidence that it is a topic. Additionally, I have investigated the relationship between agreement asymmetry and the position of the subject in MSA from the minimalist feature inheritance account viewpoint. Mainly, I reviewed null pro hypothesis which proved to be redundant to account for the derivation of VSO or SVO word orders. I have also proved what were considered agreement markers are not agreement markers but resumptive pronouns. Finally, I proved that there is not agreement asymmetry in MSA. Agreement pattern in MSA results from the agree operation and it is achieved under Probe-Goal alignment; regardless of whether the Goal is raised up to Spec-TP or remains in situ (Spec-VP), the agreement is not supposed to change. This conclusion is in harmony with the principles of MP Agree Theory. , Thesis (PhD) -- Humanities, Linguistics and Applied Language Studies, 2024
- Full Text:
Computational design for genome reduction of Lactococcus lactis towards microbial chassis development
- Authors: Hamese, Saltiel
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435321 , vital:73147
- Description: Access restricted. Expected release date 2026. , Thesis (MSc) -- Faculty of Science, Biotechnology Innovation Centre, 2024
- Full Text:
- Authors: Hamese, Saltiel
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435321 , vital:73147
- Description: Access restricted. Expected release date 2026. , Thesis (MSc) -- Faculty of Science, Biotechnology Innovation Centre, 2024
- Full Text:
Developing a community of practice to promote the use of biological control in the integrated management of Prosopis in South Africa
- Authors: Van Staden, Gretha
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434998 , vital:73122
- Description: Prosopis spp. are non-native species present in the arid parts of southern Africa. These trees originated in the Americas and were first introduced as a source of fodder, shade, and wood, but have become invasive, negatively impacting local biodiversity, and disrupting the delivery of ecosystem services. Some species of Prosopis hybridise freely, complicating identification and subsequent control. The control of Prosopis in the Northern Cape Province of South Africa is still contentious, because of the perceived benefits to some landowners. The effectiveness of biological control agents to control the spread of Prosopis has been quantified, more damaging agents have been considered in recent years because of the continued increase in Prosopis density. Research into the establishment of a Community of Practice (CoP) to address the differences in perceptions regarding the control of Prosopis in the Northern Cape Province is considered an appropriate starting point to conceptualise the challenges to the successful integrated management of Prosopis. As farmers are the main stakeholders involved with Prosopis control, understanding the role of farmers and the functioning of farming enterprises in the Northern Cape is imperative for the development of both a CoP as well as the appropriate management of Prosopis. To foster engagement with as many stakeholders as possible, workshops dealing with biological control as part on an integrated approach to the control of Prosopis were held in towns in the Northern Cape Province: Groblershoop, Brandvlei, Kenhardt, Upington, Prieska and Williston. Some of the main concerns of the landusers include the host specificity of the released biocontrol agents, as well as increased transparency and communication. This is especially in regards to the research on present and future biological control agents that will possibly improve the perceptions of stakeholders. The mechanical harvesting and use of biomass as a control method was supported, especially where farmers were removing Prosopis from their properties, leaving large amounts of biomass in the veld. Continued research into Prosopis in the Northern Cape needs to consider the possibility of secondary invasions, especially in areas where native bush encroachment is already a concern. The impact of clearing in terms of natural grazing and animal improvement needs to be quantified, to conceptualise the importance of maintaining better veld quality versus using Prosopis for fodder. Biological control targeting not only the reproductive output of the trees, but also the standing biomass has support from the majority of the land users in the Northern Cape Province following these workshops and this study shows the importance of a socio-ecological approach to the control of landscape scale invasion. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Authors: Van Staden, Gretha
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434998 , vital:73122
- Description: Prosopis spp. are non-native species present in the arid parts of southern Africa. These trees originated in the Americas and were first introduced as a source of fodder, shade, and wood, but have become invasive, negatively impacting local biodiversity, and disrupting the delivery of ecosystem services. Some species of Prosopis hybridise freely, complicating identification and subsequent control. The control of Prosopis in the Northern Cape Province of South Africa is still contentious, because of the perceived benefits to some landowners. The effectiveness of biological control agents to control the spread of Prosopis has been quantified, more damaging agents have been considered in recent years because of the continued increase in Prosopis density. Research into the establishment of a Community of Practice (CoP) to address the differences in perceptions regarding the control of Prosopis in the Northern Cape Province is considered an appropriate starting point to conceptualise the challenges to the successful integrated management of Prosopis. As farmers are the main stakeholders involved with Prosopis control, understanding the role of farmers and the functioning of farming enterprises in the Northern Cape is imperative for the development of both a CoP as well as the appropriate management of Prosopis. To foster engagement with as many stakeholders as possible, workshops dealing with biological control as part on an integrated approach to the control of Prosopis were held in towns in the Northern Cape Province: Groblershoop, Brandvlei, Kenhardt, Upington, Prieska and Williston. Some of the main concerns of the landusers include the host specificity of the released biocontrol agents, as well as increased transparency and communication. This is especially in regards to the research on present and future biological control agents that will possibly improve the perceptions of stakeholders. The mechanical harvesting and use of biomass as a control method was supported, especially where farmers were removing Prosopis from their properties, leaving large amounts of biomass in the veld. Continued research into Prosopis in the Northern Cape needs to consider the possibility of secondary invasions, especially in areas where native bush encroachment is already a concern. The impact of clearing in terms of natural grazing and animal improvement needs to be quantified, to conceptualise the importance of maintaining better veld quality versus using Prosopis for fodder. Biological control targeting not only the reproductive output of the trees, but also the standing biomass has support from the majority of the land users in the Northern Cape Province following these workshops and this study shows the importance of a socio-ecological approach to the control of landscape scale invasion. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
Functional significance of mixed-species groups for zebra (Equus quagga) in savanna habitats
- Corry-Roberts, Carys Alexandra
- Authors: Corry-Roberts, Carys Alexandra
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434925 , vital:73116
- Description: Globally, herbivore populations are facing decline, which threatens their crucial role within the ecosystems they inhabit. Herbivores are essential to ecosystem structure and function because they act as prey for higher trophic levels, cycle soil nutrients, and alter vegetation structure. Understanding the drivers that shape herbivore habitat use and selection are therefore critical for making informed conservation and management decisions. Like all prey species, herbivores must balance a trade-off between acquiring resources and avoiding predation which is influenced by a number of species-specific intrinsic traits and various ecological drivers. Herbivores can also track risk over space and time, and certain habitat structures and landscape features can influence risk perception; this is termed the landscape of fear. To mitigate the risk-reward trade-off, herbivores employ a suite of behavioural responses. Group formation is likely the most well-documented of these responses. However, grouping results in the information-competition trade-off, wherein group members may obtain valuable information regarding the location of resources and/or the risk of predation, but may suffer from increased competition, especially among larger group sizes. Mixed-species groups—an assemblage of two or more species in close spatial association—have the potential to mitigate some of the competitive costs of larger conspecific groups and enhance the anti-predator and/or foraging benefits of grouping. African savannas provide a particularly useful natural laboratory to study mixed-species groups, due to the high diversity of prey species and habitat heterogeneity present. Previous studies have investigated the mixed-species effect within these systems, but have yet to quantify some of the identity-dependent costs and benefits associated with mixed-species herding. Thus, the overall aim of my study was to quantify the functional significance of mixed-species groups for zebra (Equus quagga) herding with two of their most common herding partners, impala (Aepyceros melampus) and wildebeest (Connochaetes taurinus). My study was conducted at multiple spatial scales in the southern portion of the Kruger National Park, South Africa between 2021 and 2022. I found that mixed-species herding altered zebra landscape use, resulting in a quantifiable intensification of habitat use compared to when they herd with conspecifics. I did not observe significant habitat expansion for zebra in mixed-species herds compared to single-species herds, likely because the anti-predator benefits of mixed-species herding convey enhanced foraging opportunities in already-safe habitats. Zebra foraging with impala achieved greater foraging success and experienced lower levels of competition, compared to zebra foraging with wildebeest. However, compared to foraging with conspecifics, the levelled landscape of fear zebra experienced when foraging with wildebeest resulted in increased foraging success across the landscape. My findings highlight the context-dependency of the costs and benefits associated with different herding partners for zebra, and suggest that in mixed-species herds with wildebeest, zebra experience increased potential fitness benefits compared to herding with impala or conspecifics. Overall, the findings of my study suggest that mixed-species herding is an important tool in the suite of anti-predator behaviours employed by prey species, and one with significant implications for survivorship, habitat use, and ultimately, community level interactions. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Authors: Corry-Roberts, Carys Alexandra
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434925 , vital:73116
- Description: Globally, herbivore populations are facing decline, which threatens their crucial role within the ecosystems they inhabit. Herbivores are essential to ecosystem structure and function because they act as prey for higher trophic levels, cycle soil nutrients, and alter vegetation structure. Understanding the drivers that shape herbivore habitat use and selection are therefore critical for making informed conservation and management decisions. Like all prey species, herbivores must balance a trade-off between acquiring resources and avoiding predation which is influenced by a number of species-specific intrinsic traits and various ecological drivers. Herbivores can also track risk over space and time, and certain habitat structures and landscape features can influence risk perception; this is termed the landscape of fear. To mitigate the risk-reward trade-off, herbivores employ a suite of behavioural responses. Group formation is likely the most well-documented of these responses. However, grouping results in the information-competition trade-off, wherein group members may obtain valuable information regarding the location of resources and/or the risk of predation, but may suffer from increased competition, especially among larger group sizes. Mixed-species groups—an assemblage of two or more species in close spatial association—have the potential to mitigate some of the competitive costs of larger conspecific groups and enhance the anti-predator and/or foraging benefits of grouping. African savannas provide a particularly useful natural laboratory to study mixed-species groups, due to the high diversity of prey species and habitat heterogeneity present. Previous studies have investigated the mixed-species effect within these systems, but have yet to quantify some of the identity-dependent costs and benefits associated with mixed-species herding. Thus, the overall aim of my study was to quantify the functional significance of mixed-species groups for zebra (Equus quagga) herding with two of their most common herding partners, impala (Aepyceros melampus) and wildebeest (Connochaetes taurinus). My study was conducted at multiple spatial scales in the southern portion of the Kruger National Park, South Africa between 2021 and 2022. I found that mixed-species herding altered zebra landscape use, resulting in a quantifiable intensification of habitat use compared to when they herd with conspecifics. I did not observe significant habitat expansion for zebra in mixed-species herds compared to single-species herds, likely because the anti-predator benefits of mixed-species herding convey enhanced foraging opportunities in already-safe habitats. Zebra foraging with impala achieved greater foraging success and experienced lower levels of competition, compared to zebra foraging with wildebeest. However, compared to foraging with conspecifics, the levelled landscape of fear zebra experienced when foraging with wildebeest resulted in increased foraging success across the landscape. My findings highlight the context-dependency of the costs and benefits associated with different herding partners for zebra, and suggest that in mixed-species herds with wildebeest, zebra experience increased potential fitness benefits compared to herding with impala or conspecifics. Overall, the findings of my study suggest that mixed-species herding is an important tool in the suite of anti-predator behaviours employed by prey species, and one with significant implications for survivorship, habitat use, and ultimately, community level interactions. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
Managing releases of Anagyrus vladimiri (Triapitsyn) to augment biocontrol of the citrus mealybug Planococcus citri (Risso) in South African citrus orchards
- Authors: Mommsen, Wayne Trevor
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434952 , vital:73118
- Description: In May 2019, South Korean inspectors rejected numerous grapefruit consignments from Letsitele, Hoedspruit and Onderberg in South Arica, because of live mealybug found on fruit. Growers expressed deep concern as mealybug management to a phytosanitary level was almost unattainable. Regular spray interventions for control of citrus black spot fungus, Phyllosticta citricarpa, and citrus thrips, Scirtothrips aurantii, cause repercussions in mealybug populations because they undermine the naturally occurring biocontrol complex. As part of an Integrated Pest Management (IPM) strategy, release of commercially produced parasitoids is common practice, to augment the naturally occurring beneficial insect populations. Prior knowledge of the harmful effects of insecticides on parasitoids is essential to IPM planning and the success of the biocontrol component in such a programme. Timing of augmentative releases to coincide with the phenology of citrus and the mealybug pest is also considered important for the successful establishment and control. Consequently, field trials were conducted to compare efficacy of early vs. late releases of Anagyrus vladimiri (Triapitsyn), an effective parasitoid of the citrus mealybug, Planococcus citri (Risso). Semi-field bioassays were conducted concurrently to determine the impact of various thripicides on A. vladimiri. The impact of sulfoxaflor, spinetoram, spirotetramat and prothiofos were rated harmless, as A. vladimiri mortality was lower than 25% after coming into contact with aged residues between 7 and 14 days old. October and November releases of A. vladimiri resulted in early parasitism and lowered peak-infestation of mealybug. January releases are possibly too late in grapefruit and lemon, open field, orchards, considering parasitism by A. vladimiri peaked in February. In mandarin orchards under net, percentage parasitism of 3rd instar mealybug increased a month later. Notably, at harvest, the difference in efficacy between treatments was not clear. This could be explained by high levels of natural parasitism observed in the treated and untreated orchards, which emphasises the importance of conservation biocontrol. In a second season, the proportion of hyperparasitoids captured (61%) from samples of mealybug-infested fruit was larger than the proportion of primary parasitoids, Anagyrus vladimiri, Coccidoxenoides perminutus (Girault) and Leptomastix dactylopii (Howard) (39%), which was far lower than the captures of eclosing primary parasitoids the previous season, which was 60%. The new discovery of Pseudaphycus sp. in citrus orchards in South Africa could be a key in explaining the uncontrollable levels of mealybug experienced and has drawn attention to a need for further understanding of ecological factors that influence biological control in citrus. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
- Authors: Mommsen, Wayne Trevor
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434952 , vital:73118
- Description: In May 2019, South Korean inspectors rejected numerous grapefruit consignments from Letsitele, Hoedspruit and Onderberg in South Arica, because of live mealybug found on fruit. Growers expressed deep concern as mealybug management to a phytosanitary level was almost unattainable. Regular spray interventions for control of citrus black spot fungus, Phyllosticta citricarpa, and citrus thrips, Scirtothrips aurantii, cause repercussions in mealybug populations because they undermine the naturally occurring biocontrol complex. As part of an Integrated Pest Management (IPM) strategy, release of commercially produced parasitoids is common practice, to augment the naturally occurring beneficial insect populations. Prior knowledge of the harmful effects of insecticides on parasitoids is essential to IPM planning and the success of the biocontrol component in such a programme. Timing of augmentative releases to coincide with the phenology of citrus and the mealybug pest is also considered important for the successful establishment and control. Consequently, field trials were conducted to compare efficacy of early vs. late releases of Anagyrus vladimiri (Triapitsyn), an effective parasitoid of the citrus mealybug, Planococcus citri (Risso). Semi-field bioassays were conducted concurrently to determine the impact of various thripicides on A. vladimiri. The impact of sulfoxaflor, spinetoram, spirotetramat and prothiofos were rated harmless, as A. vladimiri mortality was lower than 25% after coming into contact with aged residues between 7 and 14 days old. October and November releases of A. vladimiri resulted in early parasitism and lowered peak-infestation of mealybug. January releases are possibly too late in grapefruit and lemon, open field, orchards, considering parasitism by A. vladimiri peaked in February. In mandarin orchards under net, percentage parasitism of 3rd instar mealybug increased a month later. Notably, at harvest, the difference in efficacy between treatments was not clear. This could be explained by high levels of natural parasitism observed in the treated and untreated orchards, which emphasises the importance of conservation biocontrol. In a second season, the proportion of hyperparasitoids captured (61%) from samples of mealybug-infested fruit was larger than the proportion of primary parasitoids, Anagyrus vladimiri, Coccidoxenoides perminutus (Girault) and Leptomastix dactylopii (Howard) (39%), which was far lower than the captures of eclosing primary parasitoids the previous season, which was 60%. The new discovery of Pseudaphycus sp. in citrus orchards in South Africa could be a key in explaining the uncontrollable levels of mealybug experienced and has drawn attention to a need for further understanding of ecological factors that influence biological control in citrus. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2024
- Full Text:
Paul and the soul: an analysis of the Apostle’s anthropology
- Authors: Pluke, Dylan Hay
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435506 , vital:73164
- Description: It may be no exaggeration to say that every aspect of the Apostle Paul’s thought is debated. This is certainly the case for his anthropology, which is to say his beliefs regarding the nature of the human person. There is intense debate concerning what Paul believed about the human person. This is especially so when arguing about whether or not Paul believed in a human soul. In the thesis that follows, I use a linguistic analysis of Paul’s writings as well as those of two of his putative backgrounds, to determine what he believed regarding the nature of the human soul. The results of this analysis are that, of the potential backgrounds that may have influenced the Apostle, the Jewish background into which he was born is the most pertinent, and that neither of the two words that Paul uses mean soul, in the sense of something which is immaterial and survives death. Rather, the psyche refers to one’s life, and the pneuma to the part of the person that connects one with God and which will replace the psyche and animate the person in the new age to come. , Thesis (MA) -- Faculty of Humanities, School of Languages and Literatures, 2024
- Full Text:
- Authors: Pluke, Dylan Hay
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435506 , vital:73164
- Description: It may be no exaggeration to say that every aspect of the Apostle Paul’s thought is debated. This is certainly the case for his anthropology, which is to say his beliefs regarding the nature of the human person. There is intense debate concerning what Paul believed about the human person. This is especially so when arguing about whether or not Paul believed in a human soul. In the thesis that follows, I use a linguistic analysis of Paul’s writings as well as those of two of his putative backgrounds, to determine what he believed regarding the nature of the human soul. The results of this analysis are that, of the potential backgrounds that may have influenced the Apostle, the Jewish background into which he was born is the most pertinent, and that neither of the two words that Paul uses mean soul, in the sense of something which is immaterial and survives death. Rather, the psyche refers to one’s life, and the pneuma to the part of the person that connects one with God and which will replace the psyche and animate the person in the new age to come. , Thesis (MA) -- Faculty of Humanities, School of Languages and Literatures, 2024
- Full Text:
Towards an artificial intelligence-based agent for characterising the organisation of primes
- Authors: Oyetunji, Nicole Armlade
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435389 , vital:73153
- Description: Machine learning has experienced significant growth in recent decades, driven by advancements in computational power and data storage. One of the applications of machine learning is in the field of number theory. Prime numbers hold significant importance in mathematics and its applications, for example in cryptography, owing to their distinct properties. Therefore, it is crucial to efficiently obtain the complete list of primes below a given threshold, with low relatively computational cost. This study extensively explores a deterministic scheme, proposed by Hawing and Okouma (2016), that is centered around Consecutive Composite Odd Numbers, showing the link between these numbers and prime numbers by examining their internal structure. The main objective of this dissertation is to develop two main artificial intelligence agents capable of learning and recognizing patterns within a list of consecutive composite odd numbers. To achieve this, the mathematical foundations of the deterministic scheme are used to generate a dataset of consecutive composite odd numbers. This dataset is further transformed into a dataset of differences to simplify the prediction problem. A literature review is conducted which encompasses research from the domains of machine learning and deep learning. Two main machine learning algorithms are implemented along with their variations, Long Short-Term Memory Networks and Error Correction Neural Networks. These models are trained independently on two separate but related datasets, the dataset of consecutive composite odd numbers and the dataset of differences between those numbers. The evaluation of these models includes relevant metrics, for example, Root Mean Square Error, Mean Absolute Percentage Error, Theil U coefficient, and Directional Accuracy. Through a comparative analysis, the study identifies the top-performing 3 models, with a particular emphasis on accuracy and computational efficiency. The results indicate that the LSTM model, when trained on difference data and coupled with exponential smoothing, displays superior performance as the most accurate model overall. It achieves a RMSE of 0.08, which significantly outperforms the dataset’s standard deviation of 0.42. This model exceeds the performance of basic estimator models, implying that a data-driven approach utilizing machine learning techniques can provide valuable insights in the field of number theory. The second best model, the ECNN trained on difference data combined with exponential smoothing, achieves an RMSE of 0.28. However, it is worth mentioning that this model is the most computationally efficient, being 32 times faster than the LSTM model. , Thesis (MSc) -- Faculty of Science, Mathematics, 2024
- Full Text:
- Authors: Oyetunji, Nicole Armlade
- Date: 2024-04-04
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/435389 , vital:73153
- Description: Machine learning has experienced significant growth in recent decades, driven by advancements in computational power and data storage. One of the applications of machine learning is in the field of number theory. Prime numbers hold significant importance in mathematics and its applications, for example in cryptography, owing to their distinct properties. Therefore, it is crucial to efficiently obtain the complete list of primes below a given threshold, with low relatively computational cost. This study extensively explores a deterministic scheme, proposed by Hawing and Okouma (2016), that is centered around Consecutive Composite Odd Numbers, showing the link between these numbers and prime numbers by examining their internal structure. The main objective of this dissertation is to develop two main artificial intelligence agents capable of learning and recognizing patterns within a list of consecutive composite odd numbers. To achieve this, the mathematical foundations of the deterministic scheme are used to generate a dataset of consecutive composite odd numbers. This dataset is further transformed into a dataset of differences to simplify the prediction problem. A literature review is conducted which encompasses research from the domains of machine learning and deep learning. Two main machine learning algorithms are implemented along with their variations, Long Short-Term Memory Networks and Error Correction Neural Networks. These models are trained independently on two separate but related datasets, the dataset of consecutive composite odd numbers and the dataset of differences between those numbers. The evaluation of these models includes relevant metrics, for example, Root Mean Square Error, Mean Absolute Percentage Error, Theil U coefficient, and Directional Accuracy. Through a comparative analysis, the study identifies the top-performing 3 models, with a particular emphasis on accuracy and computational efficiency. The results indicate that the LSTM model, when trained on difference data and coupled with exponential smoothing, displays superior performance as the most accurate model overall. It achieves a RMSE of 0.08, which significantly outperforms the dataset’s standard deviation of 0.42. This model exceeds the performance of basic estimator models, implying that a data-driven approach utilizing machine learning techniques can provide valuable insights in the field of number theory. The second best model, the ECNN trained on difference data combined with exponential smoothing, achieves an RMSE of 0.28. However, it is worth mentioning that this model is the most computationally efficient, being 32 times faster than the LSTM model. , Thesis (MSc) -- Faculty of Science, Mathematics, 2024
- Full Text:
A critical analysis of the factors influencing knowledge sharing in Indian family owned businesses in South Africa
- Authors: Sha, Shafeek
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/434817 , vital:73107 , DOI 10.21504/10962/434817
- Description: It is commonly believed that family businesses have formed the backbone of many economies around the globe and that they have been the predominant form of enterprise that has given rise to some of the most famous multinational enterprises. Family businesses contribute to the wealth creation in most economies and conservative estimates suggest that 65% to 80% of all businesses worldwide are owned and managed by families. In South Africa, Indian family owned businesses contribute more to employment than any other family business. There is a general perception amongst South Africans that Indian family owned businesses are more successful and that this success is continued from one generation to the next. Intrigued by this “phenomenon” for many years, the researcher decided to investigate it. The perspective adopted for this research was to look at the research problem from a knowledge management discipline viewpoint, in general, with a specific focus on knowledge sharing and Indian family owned businesses. The purpose of this study is to critically analyse the factors that influence the effectiveness of knowledge sharing in Indian family owned businesses. So the research answered the question: How do Indian family owned businesses in South Africa share their knowledge to ensure the continued success of their businesses through succeeding generations? A positivist research paradigm and philosophy was adopted for this research together with a quantitative research approach using survey research as the research strategy of choice. After conducting an extensive literature review, the next step was to develop and formulate a theoretical model, and flowing from the model and prior research, a research instrument was developed and administered to a qualifying sample of Indian family owned businesses in South Africa. Structural equation modelling was used as the principal mode of statistical analysis to measure the relationships amongst the variables in the model proposed in this study. After analysing the empirical data, the following key factors were identified as statistically significant in being determinants of knowledge sharing in Indian family owned businesses in South Africa: organisational culture, learning organisation, and leadership. These findings serve to contribute to the existing literature within the fields of knowledge management and family business. This study will richly contribute to research-based evidence of the factors that influence knowledge sharing in Indian family owned businesses. The outcomes will allow existing and emerging family businesses to ensure the future success of their enterprises from one generation to the next by embracing the empirical findings of this research and thus ultimately contribute to the future success of the family business as a whole. , Thesis (PhD) -- Faculty of Commerce, Management, 2024
- Full Text:
- Authors: Sha, Shafeek
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/434817 , vital:73107 , DOI 10.21504/10962/434817
- Description: It is commonly believed that family businesses have formed the backbone of many economies around the globe and that they have been the predominant form of enterprise that has given rise to some of the most famous multinational enterprises. Family businesses contribute to the wealth creation in most economies and conservative estimates suggest that 65% to 80% of all businesses worldwide are owned and managed by families. In South Africa, Indian family owned businesses contribute more to employment than any other family business. There is a general perception amongst South Africans that Indian family owned businesses are more successful and that this success is continued from one generation to the next. Intrigued by this “phenomenon” for many years, the researcher decided to investigate it. The perspective adopted for this research was to look at the research problem from a knowledge management discipline viewpoint, in general, with a specific focus on knowledge sharing and Indian family owned businesses. The purpose of this study is to critically analyse the factors that influence the effectiveness of knowledge sharing in Indian family owned businesses. So the research answered the question: How do Indian family owned businesses in South Africa share their knowledge to ensure the continued success of their businesses through succeeding generations? A positivist research paradigm and philosophy was adopted for this research together with a quantitative research approach using survey research as the research strategy of choice. After conducting an extensive literature review, the next step was to develop and formulate a theoretical model, and flowing from the model and prior research, a research instrument was developed and administered to a qualifying sample of Indian family owned businesses in South Africa. Structural equation modelling was used as the principal mode of statistical analysis to measure the relationships amongst the variables in the model proposed in this study. After analysing the empirical data, the following key factors were identified as statistically significant in being determinants of knowledge sharing in Indian family owned businesses in South Africa: organisational culture, learning organisation, and leadership. These findings serve to contribute to the existing literature within the fields of knowledge management and family business. This study will richly contribute to research-based evidence of the factors that influence knowledge sharing in Indian family owned businesses. The outcomes will allow existing and emerging family businesses to ensure the future success of their enterprises from one generation to the next by embracing the empirical findings of this research and thus ultimately contribute to the future success of the family business as a whole. , Thesis (PhD) -- Faculty of Commerce, Management, 2024
- Full Text:
Capital mobility and economic growth in South Africa
- Authors: Dhlamini, Nonceba Michelle
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434712 , vital:73098
- Description: The South African current account balance has been deteriorating over the years. An investigation of the correlation between capital mobility and economic growth is of interest as South Africa is heavily reliant on capital inflows to finance the current account deficit. This research topic is of importance as there is need to devise policies that maximise the benefits the nation derives from capital mobility. The benefits that capital flows provide economies, theoretically outweigh the disadvantages, provided that capital flows are absorbed productively. The topic is also of interest in the light of the magnitude of shocks to the South African economy such as the rand crisis, dotcom bubble, stock market bubble, inflation targeting, commodity super cycle, global financial crisis, the Covid-19 pandemic and Russo-Ukrainian War, as these shocks have translated to slower economic growth and higher levels of inflation. These shocks have equally revealed that countries need to have sound macroeconomic policies in order to survive the impact of any crises. The vision 2030 secretariat has identified capital markets as the key providers of capital required for achieving social economic blueprint. The empirical evidence locally is limited in comparison to the empirical evidence from outside of South Africa. This topic is of importance as South African studies on this topic are not as recent and this study aims to bridge that gap. Data were obtained from the South African Reserve Bank Quarterly Bulletin and the World Bank database for the period 1990 to 2022. The Autoregressive Distribution Lag model was employed in order to determine the relationship. This study relied on the supply-leading theory which posits capital markets may positively or negatively affect key indicators of economic growth. The study found that there is a positive long run relationship between net capital flows, saving-investment ratio and economic growth and a negative long run relationship between the degree of trade openness and economic growth. The findings will allow opportunity to address capital flow surges and in turn boost investor confidence. Capital flow management measures can help manage destabilizing exchange rate movements and capital flows coupled with macroprudential tools helping reduce the domestic buildup of vulnerabilities. , Thesis (MCom) -- Faculty of Commerce, Economics and Economic History, 2024
- Full Text:
- Authors: Dhlamini, Nonceba Michelle
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434712 , vital:73098
- Description: The South African current account balance has been deteriorating over the years. An investigation of the correlation between capital mobility and economic growth is of interest as South Africa is heavily reliant on capital inflows to finance the current account deficit. This research topic is of importance as there is need to devise policies that maximise the benefits the nation derives from capital mobility. The benefits that capital flows provide economies, theoretically outweigh the disadvantages, provided that capital flows are absorbed productively. The topic is also of interest in the light of the magnitude of shocks to the South African economy such as the rand crisis, dotcom bubble, stock market bubble, inflation targeting, commodity super cycle, global financial crisis, the Covid-19 pandemic and Russo-Ukrainian War, as these shocks have translated to slower economic growth and higher levels of inflation. These shocks have equally revealed that countries need to have sound macroeconomic policies in order to survive the impact of any crises. The vision 2030 secretariat has identified capital markets as the key providers of capital required for achieving social economic blueprint. The empirical evidence locally is limited in comparison to the empirical evidence from outside of South Africa. This topic is of importance as South African studies on this topic are not as recent and this study aims to bridge that gap. Data were obtained from the South African Reserve Bank Quarterly Bulletin and the World Bank database for the period 1990 to 2022. The Autoregressive Distribution Lag model was employed in order to determine the relationship. This study relied on the supply-leading theory which posits capital markets may positively or negatively affect key indicators of economic growth. The study found that there is a positive long run relationship between net capital flows, saving-investment ratio and economic growth and a negative long run relationship between the degree of trade openness and economic growth. The findings will allow opportunity to address capital flow surges and in turn boost investor confidence. Capital flow management measures can help manage destabilizing exchange rate movements and capital flows coupled with macroprudential tools helping reduce the domestic buildup of vulnerabilities. , Thesis (MCom) -- Faculty of Commerce, Economics and Economic History, 2024
- Full Text:
Effects of household debt on economic growth in South Africa
- Authors: Bwalya, Rachael Mulenga
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434766 , vital:73103
- Description: South Africa’s household debt relative to GDP has risen rapidly over the past decade. There is concern that high levels of household debt may decrease spending in the future and hence in the long run slow down economic growth. Thus, this study investigates the impact of household debt on growth in South Africa from 1987Q3 to 2022Q1. The research draws upon first-generation theories which include the absolute income hypothesis, life cycle hypothesis, and permanent income hypothesis, and second-generation theories which include the neo-Kaleckian model, the Super multiplier model, and the Steindl model. The impact of this relationship is assessed using a Vector Autoregressive (VAR) model, with a Toda-Yamamoto modification for some regressions. It is discovered that household debt has a positive short-term influence on economic growth, however, the influence is weak, and it decreases in the long run. Types of household debt such as credit card debt have shown to have a positive and strong influence on economic growth in South Africa from the short run to the long run, however, mortgage debt has shown weak positive influence on economic growth from the short 105 run to the long run. The study found that the growth maximizing ratios for household debt to 106 GDP ratio is 70 percent. The growth maximising credit card debt level is ZAR 72 403, in nominal terms and for mortgage debt is ZAR 5 980 000. The findings are expected to assist policymakers such as central banks and government authorities in formulating relevant policies to ensure economic sustainability through macro-prudential policy and strategies for household debt management. , Thesis (MEcon) -- Faculty of Commerce, Economics and Economic History, 2024
- Full Text:
- Authors: Bwalya, Rachael Mulenga
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434766 , vital:73103
- Description: South Africa’s household debt relative to GDP has risen rapidly over the past decade. There is concern that high levels of household debt may decrease spending in the future and hence in the long run slow down economic growth. Thus, this study investigates the impact of household debt on growth in South Africa from 1987Q3 to 2022Q1. The research draws upon first-generation theories which include the absolute income hypothesis, life cycle hypothesis, and permanent income hypothesis, and second-generation theories which include the neo-Kaleckian model, the Super multiplier model, and the Steindl model. The impact of this relationship is assessed using a Vector Autoregressive (VAR) model, with a Toda-Yamamoto modification for some regressions. It is discovered that household debt has a positive short-term influence on economic growth, however, the influence is weak, and it decreases in the long run. Types of household debt such as credit card debt have shown to have a positive and strong influence on economic growth in South Africa from the short run to the long run, however, mortgage debt has shown weak positive influence on economic growth from the short 105 run to the long run. The study found that the growth maximizing ratios for household debt to 106 GDP ratio is 70 percent. The growth maximising credit card debt level is ZAR 72 403, in nominal terms and for mortgage debt is ZAR 5 980 000. The findings are expected to assist policymakers such as central banks and government authorities in formulating relevant policies to ensure economic sustainability through macro-prudential policy and strategies for household debt management. , Thesis (MEcon) -- Faculty of Commerce, Economics and Economic History, 2024
- Full Text:
Short Composition Portfolio
- Authors: Mavuso, Bonelela Lindelani
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434778 , vital:73104
- Description: Short Composition Portfolio (60% performance/40%short-compositionportfolio). , Thesis (MMus) -- Faculty of Humanities, Music and Musicology, 2024
- Full Text:
- Authors: Mavuso, Bonelela Lindelani
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434778 , vital:73104
- Description: Short Composition Portfolio (60% performance/40%short-compositionportfolio). , Thesis (MMus) -- Faculty of Humanities, Music and Musicology, 2024
- Full Text:
The relationship between Environmental, Social, Governance (ESG) and Corporate Financial Performance (CFP)
- Authors: Bendeman, Justin John
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434701 , vital:73097
- Description: Restricted access. Expected release date 2025. , Thesis (MCom) -- Faculty of Commerce, Economics and Economic History, 2024
- Full Text:
- Authors: Bendeman, Justin John
- Date: 2024-04-03
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/434701 , vital:73097
- Description: Restricted access. Expected release date 2025. , Thesis (MCom) -- Faculty of Commerce, Economics and Economic History, 2024
- Full Text:
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