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
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