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:
- Date Issued: 2024-04-05
- 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:
- Date Issued: 2024-04-05
Igniting a revolution at point zero? Exploring the barriers to early learning access in South Africa and the possibility of the social economy : a comparative analysis and study of Smartstart
- Authors: McCann, Claire Mary
- Date: 2022-10-14
- Subjects: Early childhood education South Africa , Social economy South Africa , Smart Start , Education and state South Africa , Social democracy , Dual economy South Africa , South Africa Economic conditions 1991-
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/403080 , vital:69920
- Description: Economic theory suggests that the greatest return to education investment is in the earliest years; early learning and childcare may enhance skill accumulation and mothers’ labour market choices. These services may be catalytic, igniting a revolution at point zero that transforms family outcomes and aids development. In South Africa, however, early learning deficits persist. This thesis explores barriers to quality early learning access and the possibility social economy initiatives offer, focusing on social franchises like SmartStart. Document analysis, comparative analysis, and interviews with SmartStart leaders suggest two key barriers. Firstly, where private firms are dominant and ability to pay for services is limited, low-income areas are under-served. For this reason, Polanyi claims that markets should be embedded in institutions. A post-Polanyian approach emphasises the role of social investment states, which focus spending on education and where social protection scaffolds markets, in this regard. The South African state seems to embrace this approach as ECD policy frames early learning as a public good and social investment. However, a second barrier is that an insulated state enables technocratic over democratic embeddedness, with powerful rights-based discourse but poor implementation. In particular, it seems that the state lacks a framework to progressively realise the right to quality early learning. Attempts to enforce high standards are not accompanied by sufficient resources, capacity or collaboration, resulting in sub-standard services and barriers to entry. Even in better resourced contexts (e.g., Basic Education), top-down, technocratic models (re)produce failing systems, where those with means exit in favour of market alternatives. An exploration of other developing countries suggests that this failure, with variations, prevails, but also that possibility exists. In these contexts, states seem more coordinated and responsive when partnering with civil society. In South Africa, the SmartStart model is based on partnership. SmartStart frames itself as a delivery platform, building relationships with local NGOs to simultaneously scale and deepen early learning. Partnerships with communities are crucial, to build demand in a sector whose association with social reproduction means that its economic significance may be overlooked. In addition, SmartStart puts forward a child-centred approach based on a prefigurative vision but also responsive to the realities of under-resourced contexts, aiming to progressively realise rights. Though with some limitations, SmartStart’s least-cost innovation for scale provides lessons for the state. As the state’s ECD mandate shifts to Basic Education, these findings serve to inform a more effective implementation model, leveraging resources that already exist. , Thesis (MEcon) -- Faculty of Commerce, Economics and Economic History, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: McCann, Claire Mary
- Date: 2022-10-14
- Subjects: Early childhood education South Africa , Social economy South Africa , Smart Start , Education and state South Africa , Social democracy , Dual economy South Africa , South Africa Economic conditions 1991-
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/403080 , vital:69920
- Description: Economic theory suggests that the greatest return to education investment is in the earliest years; early learning and childcare may enhance skill accumulation and mothers’ labour market choices. These services may be catalytic, igniting a revolution at point zero that transforms family outcomes and aids development. In South Africa, however, early learning deficits persist. This thesis explores barriers to quality early learning access and the possibility social economy initiatives offer, focusing on social franchises like SmartStart. Document analysis, comparative analysis, and interviews with SmartStart leaders suggest two key barriers. Firstly, where private firms are dominant and ability to pay for services is limited, low-income areas are under-served. For this reason, Polanyi claims that markets should be embedded in institutions. A post-Polanyian approach emphasises the role of social investment states, which focus spending on education and where social protection scaffolds markets, in this regard. The South African state seems to embrace this approach as ECD policy frames early learning as a public good and social investment. However, a second barrier is that an insulated state enables technocratic over democratic embeddedness, with powerful rights-based discourse but poor implementation. In particular, it seems that the state lacks a framework to progressively realise the right to quality early learning. Attempts to enforce high standards are not accompanied by sufficient resources, capacity or collaboration, resulting in sub-standard services and barriers to entry. Even in better resourced contexts (e.g., Basic Education), top-down, technocratic models (re)produce failing systems, where those with means exit in favour of market alternatives. An exploration of other developing countries suggests that this failure, with variations, prevails, but also that possibility exists. In these contexts, states seem more coordinated and responsive when partnering with civil society. In South Africa, the SmartStart model is based on partnership. SmartStart frames itself as a delivery platform, building relationships with local NGOs to simultaneously scale and deepen early learning. Partnerships with communities are crucial, to build demand in a sector whose association with social reproduction means that its economic significance may be overlooked. In addition, SmartStart puts forward a child-centred approach based on a prefigurative vision but also responsive to the realities of under-resourced contexts, aiming to progressively realise rights. Though with some limitations, SmartStart’s least-cost innovation for scale provides lessons for the state. As the state’s ECD mandate shifts to Basic Education, these findings serve to inform a more effective implementation model, leveraging resources that already exist. , Thesis (MEcon) -- Faculty of Commerce, Economics and Economic History, 2022
- Full Text:
- Date Issued: 2022-10-14
Computational analysis of known drug resistant mutants of Plasmodium falciparum Dihydrofolate Reductase (PfDHFR) and screening for novel antifolates against the enzyme
- Authors: Tata, Rolland Bantar
- Date: 2022-04-08
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/234184 , vital:50170
- Description: Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
- Full Text:
- Date Issued: 2022-04-08
- Authors: Tata, Rolland Bantar
- Date: 2022-04-08
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/234184 , vital:50170
- Description: Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
- Full Text:
- Date Issued: 2022-04-08
Characterisation of the ultramafic and carbonatite components of the Schiel Alkaline Complex in the Limpopo Province of South Africa
- Authors: Mahomed, Uzayr
- Date: 2021-10-29
- Subjects: Ultrabasic rocks South Africa Limpopo , Carbonatites South Africa Limpopo , Geology South Africa Limpopo , Mica South Africa Limpopo , Biotite South Africa Limpopo , Magmatism , Schiel Alkaline Complex , Phoscorite , Glimmerite
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/294768 , vital:57253
- Description: Owing to the poor documentation of the phoscorite-carbonatite association present in the Schiel Complex and the associated economic potential of other known phoscorite-bearing complexes, the Schiel Complex is widely thought to have similar economic potential. This complex is often compared to the lucrative Phalaborwa Complex, as it is thought to have crystallised from a common parental melt, with a similar age of emplacement. This study aims to provide clarity on the physical and chemical characterisation of the various rock types present in the Schiel Complex, with this study being the first petrological investigation based on fresh in-situ samples gathered from 3 borehole cores which were drilled by FOSKOR in the 1960s. The sampled sections of the ultramafics from the Schiel Complex are comprised of end-member rock compositions of either magmatic phoscorites or pyroxenites or metasomatic glimmerites, where gradational contacts between these various end-members produce rock varieties that contain characteristics of one or more end-member types. Carbonatite rocks are present as medium-grained, coarse-grained and banded calcio-carbonatite varieties where the carbonatite rocks are proposed as being the metasomatic medium for glimmerite production. Contrary to previous research, the structure of the ultramafic and carbonatite bodies are present as vein and veinlet structures which seem to originate from a single pipe-like body, from which these rock types intruded into the surrounding syenitic country-rock. Metasomatic alteration of the ultramafic sections of the Schiel Complex also show that the carbonatite rocks must have intruded after some ultramafic magmatism. The presence of the same minerals, with similar chemistries, in both the ultramafic and carbonatite rocks as well as similar REE chondrite-normalised plots show that the various rock types may have originated from a common parental magma, where the accumulation and crystallisation of minerals is the most likely factor in producing the various Schiel Complex rock varieties, causing silicate minerals to be present in the carbonate fraction of the magma, and carbonate minerals in the silicate fraction of the magma. Apatite is the expected rare earth element (REE) mineralising mineral in phoscorites, but is shown to be depleted in REE content in the Schiel Complex due to metasomatic fluid infiltration causing the scavenging and dissipation of REEs. These rocks have also crystallised containing no significant copper-bearing mineralisation, contrary to that which is seen in the Phalaborwa Complex. A comparison of mica minerals between the Schiel Complex rocks and the Phalaborwa Complex rocks show that the two complexes have undergone unique emplacement processes and should not be considered as sister complexes. Efforts to date the glimmerite and carbonatite rocks based on zircon grain U/Pb geochronology proved unsuccessful in constraining the current ages of emplacement provided by previous researchers, but rock relationships show that the current accepted sequence of events cannot be correct, providing scope for further research. This study provides an update on the chemical and physical characteristics, based on the only available sample suite of the ultramafic and carbonatite components, of the Schiel Complex, increasing the depth of documentation of these rare rock types and aiding in refuting some conclusions on the genesis, emplacement and evolution of the Schiel Complex proposed by previous research. , Thesis (MSc) -- Faculty of Science, Geology, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Mahomed, Uzayr
- Date: 2021-10-29
- Subjects: Ultrabasic rocks South Africa Limpopo , Carbonatites South Africa Limpopo , Geology South Africa Limpopo , Mica South Africa Limpopo , Biotite South Africa Limpopo , Magmatism , Schiel Alkaline Complex , Phoscorite , Glimmerite
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/294768 , vital:57253
- Description: Owing to the poor documentation of the phoscorite-carbonatite association present in the Schiel Complex and the associated economic potential of other known phoscorite-bearing complexes, the Schiel Complex is widely thought to have similar economic potential. This complex is often compared to the lucrative Phalaborwa Complex, as it is thought to have crystallised from a common parental melt, with a similar age of emplacement. This study aims to provide clarity on the physical and chemical characterisation of the various rock types present in the Schiel Complex, with this study being the first petrological investigation based on fresh in-situ samples gathered from 3 borehole cores which were drilled by FOSKOR in the 1960s. The sampled sections of the ultramafics from the Schiel Complex are comprised of end-member rock compositions of either magmatic phoscorites or pyroxenites or metasomatic glimmerites, where gradational contacts between these various end-members produce rock varieties that contain characteristics of one or more end-member types. Carbonatite rocks are present as medium-grained, coarse-grained and banded calcio-carbonatite varieties where the carbonatite rocks are proposed as being the metasomatic medium for glimmerite production. Contrary to previous research, the structure of the ultramafic and carbonatite bodies are present as vein and veinlet structures which seem to originate from a single pipe-like body, from which these rock types intruded into the surrounding syenitic country-rock. Metasomatic alteration of the ultramafic sections of the Schiel Complex also show that the carbonatite rocks must have intruded after some ultramafic magmatism. The presence of the same minerals, with similar chemistries, in both the ultramafic and carbonatite rocks as well as similar REE chondrite-normalised plots show that the various rock types may have originated from a common parental magma, where the accumulation and crystallisation of minerals is the most likely factor in producing the various Schiel Complex rock varieties, causing silicate minerals to be present in the carbonate fraction of the magma, and carbonate minerals in the silicate fraction of the magma. Apatite is the expected rare earth element (REE) mineralising mineral in phoscorites, but is shown to be depleted in REE content in the Schiel Complex due to metasomatic fluid infiltration causing the scavenging and dissipation of REEs. These rocks have also crystallised containing no significant copper-bearing mineralisation, contrary to that which is seen in the Phalaborwa Complex. A comparison of mica minerals between the Schiel Complex rocks and the Phalaborwa Complex rocks show that the two complexes have undergone unique emplacement processes and should not be considered as sister complexes. Efforts to date the glimmerite and carbonatite rocks based on zircon grain U/Pb geochronology proved unsuccessful in constraining the current ages of emplacement provided by previous researchers, but rock relationships show that the current accepted sequence of events cannot be correct, providing scope for further research. This study provides an update on the chemical and physical characteristics, based on the only available sample suite of the ultramafic and carbonatite components, of the Schiel Complex, increasing the depth of documentation of these rare rock types and aiding in refuting some conclusions on the genesis, emplacement and evolution of the Schiel Complex proposed by previous research. , Thesis (MSc) -- Faculty of Science, Geology, 2021
- Full Text:
- Date Issued: 2021-10-29
Integrative systematic structuring of the widespread psammophiid snakes (Psammophiidae): a multi-evidence species delineation approach
- Authors: Keates, Chad
- Date: 2021-10-29
- Subjects: Psammophis South Africa , Herpetology , Herpetology Africa , Molecular biology , Psammophis Classification , Psammophis Genetics , Psammophis Morphology , Psammophis Phylogeny , Morphology Mathematics , Psammophylax
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/295077 , vital:57288 , DOI 10.21504/10962/295079
- Description: Species form the foundations upon which we build our understanding of the natural world. Although a focus of much scientific attention, our understanding of species is stunted by the intrinsic ‘fuzziness’ of boundaries within nature. Due to the complexity of the evolutionary process, coupled with an ever-changing abiotic landscape, species are hard to delineate, even at the best of times. Whilst various species concepts and sophisticated delimitation methods have helped scientists tease apart species, many species complexes persist. This is because taxonomy is a discrete ordering system imposed upon the continuous and intercalated structure of life. To improve our understanding of a wide-ranging family of snakes, I investigated the taxonomy and evolutionary structuring within Psammophiidae using both molecular and morphological approaches, employing phylogenetic, phylogeographic, and morphometric analyses on the group. The systematic complexity of the family (as evidenced by past research) coupled with the group’s widespread distribution and ecological importance, made the taxon an ideal candidate for a broad-sweeping multi-level systematic analysis using multiple species delimitation methods. Additionally, in this thesis I attempted to build on the ground-breaking work of Christopher Kelly by addressing several knowledge gaps identified within the family, and in so doing, produce the most thorough evolutionary and taxonomic study of Psammophiidae possible. Given the taxonomic uncertainty associated with the family, Chapter Two used a representative sampling from every available species (near complete taxon sampling approach) in the family. The chapter used both standard and time-calibrated phylogenetic modelling and distance/threshold-based species delimitation, to elucidate the finer-level structuring within the family. Geometric morphometrics was used to determine whether there were diagnosable differences in head structure between the different genera. The final phylogenetic tree incorporated 320 samples, representing the most comprehensive phylogenetic reconstruction of the family to date. By using a near-complete taxon sampling approach, I was able to resolve previously unsupported relationships within the family whilst also identifying several novel instances of an under- and over-appreciation of species diversity within the family. Geometric morphometrics also identified clear distinctions between genera based on head shape (head width and ‘beakedness’). This chapter showcased the importance of complete taxon sampling and robust methodology for species delimitation and the deleterious effect of species concepts when implemented in isolation. In Chapter Three, I narrowed the scope of the study to focus on the genus level. Psammophylax (Fitzinger 1843) is an abundant, yet poorly studied genus of grass snakes, endemic to Africa. The generalist nature of the genus and wide-spanning distributions of the constituent species has given rise to several subspecies and a poor understanding of the taxonomic structuring within the genus. The overlapping distributions (sympatry) of many of Psammophylax species, coupled with the potential for cryptic speciation via mechanisms such as convergent evolution, made the group the ideal candidate for a broad-sweeping systematic study (as evidenced in Chapter Two). By applying the suite of analyses used in Chapter Two to the generic level, we aimed to determine the effectiveness of a multi-evidence species delineation approach when tackling systematic problems at lower taxonomic levels. A genetic phylogeny of six of the seven species was estimated using multiple phylogenetic and distance/ threshold-based species delimitation methods. To support the molecular analyses, we conducted morphological analyses on the body (traditional morphology) and head (geometric morphometrics) separately. Phylogenetic analyses recovered a similar topology to past studies, but with better resolution and node support. I found substantial genetic structuring within the genus, supported by significantly different head shapes between Ps. a. acutus and other Psammophylax species. Psammophylax a. acutus was recovered as sister to its congeners, and sequence divergence values and morphometrics supported its recognition as a new genus. Increased sampling in East Africa (Tanzania, Kenya, and Ethiopia) revealed that Psammophylax multisquamis is polyphyletic, necessitating the description of a new, morphologically cryptic, species from northern Tanzania. The distribution of Ps. multisquamis sensu stricto is likely restricted to Kenya and Ethiopia. Within this chapter, taxon-specific phylogenetic analyses yielded stronger intrageneric support as compared to Chapter Two, allowing for more defensible conclusions about taxonomical amendments. Geometric morphometrics proved similarly useful (as compared to Chapter Two) in teasing apart genera within the family but lacked the robustness to delineate species within Psammophylax with confidence, highlighting the apparent convergence of form within the genus. In Chapter Four, I investigated the evolutionary structuring within the Southern African endemic Psammophylax rhombeatus. The structural and environmental heterogeneity within the region has given rise to many morphological forms distributed throughout the country, with previous studies neglecting the associated molecular significance of these forms. Irrespective of their small sample sizes, both Chapter Two and Three identified substantial phylogenetic structuring within the species, making Ps. rhombeatus the ideal candidate for a multi-faceted systematic review, using a combination of phylogenetics, geometric morphometrics and, for the first time in this species, phylogeographic analyses. By investigating a single species, in detail, I was able to assess the effectiveness of the methodologies implemented in previous chapters on systematic sorting using the multi-evidence species delineation approach. Phylogenetic and haplotype analysis retrieved four well-supported clades: southeast South Africa (SESA), southwest South Africa (SWSA), north-eastern South Africa (NESA) and western South Africa (WSA). Although not variable enough to warrant taxonomic re-evaluation, the clades represented important genetic hotspots, with relatively high intraspecific genetic divergence values separating them, irrespective of the small geographic distances separating populations. This is likely a product of the taxon’s habitat-generalist lifestyle, enabling them to bypass vicariant barriers that might otherwise cause speciation in less versatile species. The clades are also geographically distinct, with little overlap, indicating previous vicariance, a finding that is supported by the split of Ps. rhombeatus from Ps. ocellatus in the mid-Pliocene, followed by the diversification of Ps. rhombeatus into four clades throughout the Pleistocene. The genetic structuring observed in Ps. rhombeatus may be a product of population expansion following ancient refugial isolation (potentially Last Glacial Maximum [LGM]). The molecular distinctiveness of the clades was not replicated in the morphological component of this chapter, with neither dorsal nor lateral geometric morphometric analyses of head shape showing any discernible distinctiveness based on geography. Whilst head shape has not been shown to be an effective delineator of evolutionary units at the species level (within this taxon), body colour, scalation, and snout-vent length has been linked to morphotypes within the species based on the work of Broadley (1966). These morphological groupings are loosely attributable to the molecular clades identified in the phylogenetic analyses, highlighting the complex interplay of genetic and morphological characteristics in the process of speciation, and their representation in systematic accounts. This thesis represents the most thorough evolutionary and systematic study of the family currently possible. In addition to identifying and describing both a new genus and species, this thesis also highlighted several instances of an over- and under-appreciation of species diversity within Psammophiidae. By applying a multi-evidence species delineation approach to this thesis, I show the intricacy of the evolutionary process (at various taxonomic levels) and showcase the ease to which species boundaries can be confounded when species concepts are implemented in isolation. These findings also highlighted the importance of sample size, sample range, species delimitation method on the outcome of taxonomic analyses, and their interpretation. Lastly, this thesis addressed the knowledge gaps left by Christopher Kelly’s PhD work and investigated the findings of recent papers that attempted to do the same. Whilst this study answers the questions of old, the taxon-intensive focus revealed several new knowledge gaps within the family, highlighting how much we know about snake systematics, and furthermore, how much we still need to learn about evolutionary structuring. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Keates, Chad
- Date: 2021-10-29
- Subjects: Psammophis South Africa , Herpetology , Herpetology Africa , Molecular biology , Psammophis Classification , Psammophis Genetics , Psammophis Morphology , Psammophis Phylogeny , Morphology Mathematics , Psammophylax
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/295077 , vital:57288 , DOI 10.21504/10962/295079
- Description: Species form the foundations upon which we build our understanding of the natural world. Although a focus of much scientific attention, our understanding of species is stunted by the intrinsic ‘fuzziness’ of boundaries within nature. Due to the complexity of the evolutionary process, coupled with an ever-changing abiotic landscape, species are hard to delineate, even at the best of times. Whilst various species concepts and sophisticated delimitation methods have helped scientists tease apart species, many species complexes persist. This is because taxonomy is a discrete ordering system imposed upon the continuous and intercalated structure of life. To improve our understanding of a wide-ranging family of snakes, I investigated the taxonomy and evolutionary structuring within Psammophiidae using both molecular and morphological approaches, employing phylogenetic, phylogeographic, and morphometric analyses on the group. The systematic complexity of the family (as evidenced by past research) coupled with the group’s widespread distribution and ecological importance, made the taxon an ideal candidate for a broad-sweeping multi-level systematic analysis using multiple species delimitation methods. Additionally, in this thesis I attempted to build on the ground-breaking work of Christopher Kelly by addressing several knowledge gaps identified within the family, and in so doing, produce the most thorough evolutionary and taxonomic study of Psammophiidae possible. Given the taxonomic uncertainty associated with the family, Chapter Two used a representative sampling from every available species (near complete taxon sampling approach) in the family. The chapter used both standard and time-calibrated phylogenetic modelling and distance/threshold-based species delimitation, to elucidate the finer-level structuring within the family. Geometric morphometrics was used to determine whether there were diagnosable differences in head structure between the different genera. The final phylogenetic tree incorporated 320 samples, representing the most comprehensive phylogenetic reconstruction of the family to date. By using a near-complete taxon sampling approach, I was able to resolve previously unsupported relationships within the family whilst also identifying several novel instances of an under- and over-appreciation of species diversity within the family. Geometric morphometrics also identified clear distinctions between genera based on head shape (head width and ‘beakedness’). This chapter showcased the importance of complete taxon sampling and robust methodology for species delimitation and the deleterious effect of species concepts when implemented in isolation. In Chapter Three, I narrowed the scope of the study to focus on the genus level. Psammophylax (Fitzinger 1843) is an abundant, yet poorly studied genus of grass snakes, endemic to Africa. The generalist nature of the genus and wide-spanning distributions of the constituent species has given rise to several subspecies and a poor understanding of the taxonomic structuring within the genus. The overlapping distributions (sympatry) of many of Psammophylax species, coupled with the potential for cryptic speciation via mechanisms such as convergent evolution, made the group the ideal candidate for a broad-sweeping systematic study (as evidenced in Chapter Two). By applying the suite of analyses used in Chapter Two to the generic level, we aimed to determine the effectiveness of a multi-evidence species delineation approach when tackling systematic problems at lower taxonomic levels. A genetic phylogeny of six of the seven species was estimated using multiple phylogenetic and distance/ threshold-based species delimitation methods. To support the molecular analyses, we conducted morphological analyses on the body (traditional morphology) and head (geometric morphometrics) separately. Phylogenetic analyses recovered a similar topology to past studies, but with better resolution and node support. I found substantial genetic structuring within the genus, supported by significantly different head shapes between Ps. a. acutus and other Psammophylax species. Psammophylax a. acutus was recovered as sister to its congeners, and sequence divergence values and morphometrics supported its recognition as a new genus. Increased sampling in East Africa (Tanzania, Kenya, and Ethiopia) revealed that Psammophylax multisquamis is polyphyletic, necessitating the description of a new, morphologically cryptic, species from northern Tanzania. The distribution of Ps. multisquamis sensu stricto is likely restricted to Kenya and Ethiopia. Within this chapter, taxon-specific phylogenetic analyses yielded stronger intrageneric support as compared to Chapter Two, allowing for more defensible conclusions about taxonomical amendments. Geometric morphometrics proved similarly useful (as compared to Chapter Two) in teasing apart genera within the family but lacked the robustness to delineate species within Psammophylax with confidence, highlighting the apparent convergence of form within the genus. In Chapter Four, I investigated the evolutionary structuring within the Southern African endemic Psammophylax rhombeatus. The structural and environmental heterogeneity within the region has given rise to many morphological forms distributed throughout the country, with previous studies neglecting the associated molecular significance of these forms. Irrespective of their small sample sizes, both Chapter Two and Three identified substantial phylogenetic structuring within the species, making Ps. rhombeatus the ideal candidate for a multi-faceted systematic review, using a combination of phylogenetics, geometric morphometrics and, for the first time in this species, phylogeographic analyses. By investigating a single species, in detail, I was able to assess the effectiveness of the methodologies implemented in previous chapters on systematic sorting using the multi-evidence species delineation approach. Phylogenetic and haplotype analysis retrieved four well-supported clades: southeast South Africa (SESA), southwest South Africa (SWSA), north-eastern South Africa (NESA) and western South Africa (WSA). Although not variable enough to warrant taxonomic re-evaluation, the clades represented important genetic hotspots, with relatively high intraspecific genetic divergence values separating them, irrespective of the small geographic distances separating populations. This is likely a product of the taxon’s habitat-generalist lifestyle, enabling them to bypass vicariant barriers that might otherwise cause speciation in less versatile species. The clades are also geographically distinct, with little overlap, indicating previous vicariance, a finding that is supported by the split of Ps. rhombeatus from Ps. ocellatus in the mid-Pliocene, followed by the diversification of Ps. rhombeatus into four clades throughout the Pleistocene. The genetic structuring observed in Ps. rhombeatus may be a product of population expansion following ancient refugial isolation (potentially Last Glacial Maximum [LGM]). The molecular distinctiveness of the clades was not replicated in the morphological component of this chapter, with neither dorsal nor lateral geometric morphometric analyses of head shape showing any discernible distinctiveness based on geography. Whilst head shape has not been shown to be an effective delineator of evolutionary units at the species level (within this taxon), body colour, scalation, and snout-vent length has been linked to morphotypes within the species based on the work of Broadley (1966). These morphological groupings are loosely attributable to the molecular clades identified in the phylogenetic analyses, highlighting the complex interplay of genetic and morphological characteristics in the process of speciation, and their representation in systematic accounts. This thesis represents the most thorough evolutionary and systematic study of the family currently possible. In addition to identifying and describing both a new genus and species, this thesis also highlighted several instances of an over- and under-appreciation of species diversity within Psammophiidae. By applying a multi-evidence species delineation approach to this thesis, I show the intricacy of the evolutionary process (at various taxonomic levels) and showcase the ease to which species boundaries can be confounded when species concepts are implemented in isolation. These findings also highlighted the importance of sample size, sample range, species delimitation method on the outcome of taxonomic analyses, and their interpretation. Lastly, this thesis addressed the knowledge gaps left by Christopher Kelly’s PhD work and investigated the findings of recent papers that attempted to do the same. Whilst this study answers the questions of old, the taxon-intensive focus revealed several new knowledge gaps within the family, highlighting how much we know about snake systematics, and furthermore, how much we still need to learn about evolutionary structuring. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2021
- Full Text:
- Date Issued: 2021-10-29
A behaviour of South Africa’s economy towards inflows of foreign direct investment (FDI) from BRICs economies
- Authors: Dingela, Siyasanga
- Date: 2021-04
- Subjects: Investments, Foreign -- South Africa , Investments, Foreign -- Developing countries , South Africa -- Economic conditions , BRIC countries -- Foreign economic relations
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/51141 , vital:43212
- Description: This study investigated a behaviour of South Africa’s economy towards inflows of foreign direct investment (FDI) from Brazil, Russia, India and China (BRICs) economies, during the period 1997 to 2016. The BRICs bloc was coined in 2001 by then chairperson of Goldman Sachs Asset Management, Jim O’Neil. According to Goldman Sach (2001), the BRICs group was collectively expected to overtake the major economic powers over the span of a few decades. Their growth is expected to shape a new economic order and replace the currently dominant advanced economies. South Africa joined the BRICs bloc in 2010 as the jeweler of the world and as a gateway to Africa. It joined the BRICs group at the time when economic growth was at a sluggish rate, and the savings and investment were at the lowest rate. The country had a high unemployment rate, high levels of poverty and income inequality. On the other hand, the BRICs economies had limited intra-BRICs flows amongst themselves. It is against this background that this study investigated the long run impact of BRICs FDI inflows on South Africa’s economic growth, and the causality relationship between South Africa’s economic growth and BRICs FDI inflows. This study contributes to the body of knowledge of economics in South Africa and the literature on foreign direct investment and economic growth in South Africa. The study employed two cointegration methods to investigate the behaviour of South Africa’s economy towards inflows of foreign direct investment from BRICs economies. These are fully modified ordinary least squares (FMOLS) and dynamic ordinary least squares (DOLS). For granger causality, the study employed Stacked and Dumistrescu Hurlin tests. All the models used time series annual data from 1997 to 2016. The Unit root test results confirmed that the variables were stationary at first difference using panel Im, Pesaran, Shin (IPS) and Levin, Lin, Chu (LLC). The research employs four regressions, first, Economic growth and foreign direct investment (i.e. private sector, banking sector and both sectors), human capital, physical capital, household consumption, government expenditure, exports, and arable land; Second, Employment and foreign direct investment, human capital, physical capital, household consumption, government expenditure, exports, and arable land; third, Economic complexity and foreign direct investment, human capital, physical capital, household consumption, government expenditure, exports, and arable land; finally, Unemployment and foreign direct investment, human capital, physical capital, household consumption, government expenditure, exports, and arable land. The cointegration results for private FDI and economic growth, employment, economic complexity, and unemployment. The results show only economic complexity has significant effect on foreign direct investment and other variables show insignificant results. However, this effect is smaller compared to other growth determinants which are included in the regressions. The cointegration results for bank FDI. These results show more similarities with private FDI results and few differences. However, this effect is smaller compared to other growth determinants included in the regressions. These growth determinants, however, show a positive effect of human capital and household consumption on economic growth which is expected. Other interesting results are exports being positively related with economic growth and unemployment but negative with employment and insignificant with economic complexity. Another one is government spending negatively influence economic growth, employment and positively influence unemployment. But insignificant for economic complexity. Total FDI results and other variables. These results are also similar to private and bank FDI results discussed above. Economic complexity shows significant effect with foreign direct investment, yet other variables are insignificant. . Further results show human capital positively related with economic growth, which is expected. However, physical capital and household consumption negatively affects growth. Another one exports show positive influence on economic growth but negatively related with employment. Yet, insignificant with economic complexity and unemployment. Other results government spending shows negative influence with employment but insignificant with economic growth, economic complexity and unemployment. The results for nonlinearity between the variables under review. The results that employment and economic complexity are nonlinear with foreign direct investment and no nonlinearity between unemployment, economic growth and foreign direct investment. For employment, low levels of foreign direct investment (LFDI_private) adversely affects employment but at higher levels (FDI_private_SQ) is insignificant. For economic complexity, low levels of foreign direct investment are insignificant for economic complexity but at higher levels there is a positive effect of squared foreign direct investment on economic complexity. Further results show that economic growth and employment are nonlinear with human capital, physical capital, household consumption and exports. Physical capital and household consumption adversely affect economic growth, yet positively affects employment. Human capital positively affects economic growth, employment, and unemployment. Exports positively affect economic growth, but negatively affect employment. Further results show nonlinearity between employment and government expenditure. Government expenditure adversely affects employment. Also, economic growth and unemployment show nonlinearity with arable land. Arable land adversely affects economic growth but positively affects unemployment. Nonlinear results for economic growth and economic complexity with foreign direct investment but no nonlinearity in other remaining variables. For economic growth, low levels of foreign direct investment there is a positive effect of foreign direct investment on economic growth, however, at higher levels foreign direct investment are insignificant. For economic complexity, low levels of foreign direct investment are insignificant, yet, higher levels of foreign direct investment there is a positive influence of foreign direct investment on economic complexity. Further results show economic growth and employment that are nonlinear with human capital, physical capital, and household consumption. Human capital positively affects both economic growth and employment. Physical capital and household consumption are adversely affecting economic growth, yet positively affects employment. Further results show nonlinearity between economic growth and government expenditure. Government expenditure adversely affects employment. More results, employment, and unemployment show nonlinearity results with exports. Exports adversely affect employment but positively affects unemployment. Results show economic growth and unemployment that are nonlinear with arable land. Arable land adversely affects economic growth, but positively affect unemployment. Nonlinear results for economic complexity only and other variables show no nonlinearity in the regressions. For economic complexity, low levels of foreign direct investment are insignificant, but at higher levels of foreign direct investment there is positive effect of foreign direct investment on economic complexity. More results show economic growth and employment that are nonlinear with human capital, physical capital, household consumption and exports. Human capital and exports positively affect economic growth, employment, and unemployment. Whereas, physical capital and household consumption adversely affects economic growth and unemployment, yet positively affects employment. Further results show nonlinearity between employment and government expenditure. Government spending adversely affects employment. Further results show nonlinearity between economic growth and unemployment with arable land. Arable land positively affects unemployment, yet adversely affects economic growth. The following section discusses granger causality results. This study also employed granger causality tests. The causality results between economic growth, employment, economic complexity, unemployment, and private foreign direct investment. The causality results show that there is granger causality between economic growth and economic complexity with private foreign direct investment. Whereas, between bank foreign direct investment and other variables there is no granger causality. However, between total foreign direct investment and economic growth and employment there is granger causality. There are a number of policy recommendations that can be drawn from the study. The study results in overall revealed that BRICs (private and bank) FDI inflows had a positive impact on South Africa’s economic growth between 1997 and 2016. The study results suggest that the policy makers should focus the attention on lobbying foreign direct investment from BRICs economies, since this study shows positive impact and relationship between South Africa’s economic growth and BRICs FDI inflows. The BRICs economies should focus on enhancing investment partnership, preventing protectionism, and promoting intra-BRICS flows. In addition, South Africa should eliminate barriers affecting business with BRICs countries. Policy makers should promote the building of new companies (for example Greenfield Investment) so that the economy of South Africa could grow and create employment. , Thesis (MA) -- Faculty of Business and Economic Sciences, Economics, 2021
- Full Text:
- Date Issued: 2021-04
- Authors: Dingela, Siyasanga
- Date: 2021-04
- Subjects: Investments, Foreign -- South Africa , Investments, Foreign -- Developing countries , South Africa -- Economic conditions , BRIC countries -- Foreign economic relations
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/51141 , vital:43212
- Description: This study investigated a behaviour of South Africa’s economy towards inflows of foreign direct investment (FDI) from Brazil, Russia, India and China (BRICs) economies, during the period 1997 to 2016. The BRICs bloc was coined in 2001 by then chairperson of Goldman Sachs Asset Management, Jim O’Neil. According to Goldman Sach (2001), the BRICs group was collectively expected to overtake the major economic powers over the span of a few decades. Their growth is expected to shape a new economic order and replace the currently dominant advanced economies. South Africa joined the BRICs bloc in 2010 as the jeweler of the world and as a gateway to Africa. It joined the BRICs group at the time when economic growth was at a sluggish rate, and the savings and investment were at the lowest rate. The country had a high unemployment rate, high levels of poverty and income inequality. On the other hand, the BRICs economies had limited intra-BRICs flows amongst themselves. It is against this background that this study investigated the long run impact of BRICs FDI inflows on South Africa’s economic growth, and the causality relationship between South Africa’s economic growth and BRICs FDI inflows. This study contributes to the body of knowledge of economics in South Africa and the literature on foreign direct investment and economic growth in South Africa. The study employed two cointegration methods to investigate the behaviour of South Africa’s economy towards inflows of foreign direct investment from BRICs economies. These are fully modified ordinary least squares (FMOLS) and dynamic ordinary least squares (DOLS). For granger causality, the study employed Stacked and Dumistrescu Hurlin tests. All the models used time series annual data from 1997 to 2016. The Unit root test results confirmed that the variables were stationary at first difference using panel Im, Pesaran, Shin (IPS) and Levin, Lin, Chu (LLC). The research employs four regressions, first, Economic growth and foreign direct investment (i.e. private sector, banking sector and both sectors), human capital, physical capital, household consumption, government expenditure, exports, and arable land; Second, Employment and foreign direct investment, human capital, physical capital, household consumption, government expenditure, exports, and arable land; third, Economic complexity and foreign direct investment, human capital, physical capital, household consumption, government expenditure, exports, and arable land; finally, Unemployment and foreign direct investment, human capital, physical capital, household consumption, government expenditure, exports, and arable land. The cointegration results for private FDI and economic growth, employment, economic complexity, and unemployment. The results show only economic complexity has significant effect on foreign direct investment and other variables show insignificant results. However, this effect is smaller compared to other growth determinants which are included in the regressions. The cointegration results for bank FDI. These results show more similarities with private FDI results and few differences. However, this effect is smaller compared to other growth determinants included in the regressions. These growth determinants, however, show a positive effect of human capital and household consumption on economic growth which is expected. Other interesting results are exports being positively related with economic growth and unemployment but negative with employment and insignificant with economic complexity. Another one is government spending negatively influence economic growth, employment and positively influence unemployment. But insignificant for economic complexity. Total FDI results and other variables. These results are also similar to private and bank FDI results discussed above. Economic complexity shows significant effect with foreign direct investment, yet other variables are insignificant. . Further results show human capital positively related with economic growth, which is expected. However, physical capital and household consumption negatively affects growth. Another one exports show positive influence on economic growth but negatively related with employment. Yet, insignificant with economic complexity and unemployment. Other results government spending shows negative influence with employment but insignificant with economic growth, economic complexity and unemployment. The results for nonlinearity between the variables under review. The results that employment and economic complexity are nonlinear with foreign direct investment and no nonlinearity between unemployment, economic growth and foreign direct investment. For employment, low levels of foreign direct investment (LFDI_private) adversely affects employment but at higher levels (FDI_private_SQ) is insignificant. For economic complexity, low levels of foreign direct investment are insignificant for economic complexity but at higher levels there is a positive effect of squared foreign direct investment on economic complexity. Further results show that economic growth and employment are nonlinear with human capital, physical capital, household consumption and exports. Physical capital and household consumption adversely affect economic growth, yet positively affects employment. Human capital positively affects economic growth, employment, and unemployment. Exports positively affect economic growth, but negatively affect employment. Further results show nonlinearity between employment and government expenditure. Government expenditure adversely affects employment. Also, economic growth and unemployment show nonlinearity with arable land. Arable land adversely affects economic growth but positively affects unemployment. Nonlinear results for economic growth and economic complexity with foreign direct investment but no nonlinearity in other remaining variables. For economic growth, low levels of foreign direct investment there is a positive effect of foreign direct investment on economic growth, however, at higher levels foreign direct investment are insignificant. For economic complexity, low levels of foreign direct investment are insignificant, yet, higher levels of foreign direct investment there is a positive influence of foreign direct investment on economic complexity. Further results show economic growth and employment that are nonlinear with human capital, physical capital, and household consumption. Human capital positively affects both economic growth and employment. Physical capital and household consumption are adversely affecting economic growth, yet positively affects employment. Further results show nonlinearity between economic growth and government expenditure. Government expenditure adversely affects employment. More results, employment, and unemployment show nonlinearity results with exports. Exports adversely affect employment but positively affects unemployment. Results show economic growth and unemployment that are nonlinear with arable land. Arable land adversely affects economic growth, but positively affect unemployment. Nonlinear results for economic complexity only and other variables show no nonlinearity in the regressions. For economic complexity, low levels of foreign direct investment are insignificant, but at higher levels of foreign direct investment there is positive effect of foreign direct investment on economic complexity. More results show economic growth and employment that are nonlinear with human capital, physical capital, household consumption and exports. Human capital and exports positively affect economic growth, employment, and unemployment. Whereas, physical capital and household consumption adversely affects economic growth and unemployment, yet positively affects employment. Further results show nonlinearity between employment and government expenditure. Government spending adversely affects employment. Further results show nonlinearity between economic growth and unemployment with arable land. Arable land positively affects unemployment, yet adversely affects economic growth. The following section discusses granger causality results. This study also employed granger causality tests. The causality results between economic growth, employment, economic complexity, unemployment, and private foreign direct investment. The causality results show that there is granger causality between economic growth and economic complexity with private foreign direct investment. Whereas, between bank foreign direct investment and other variables there is no granger causality. However, between total foreign direct investment and economic growth and employment there is granger causality. There are a number of policy recommendations that can be drawn from the study. The study results in overall revealed that BRICs (private and bank) FDI inflows had a positive impact on South Africa’s economic growth between 1997 and 2016. The study results suggest that the policy makers should focus the attention on lobbying foreign direct investment from BRICs economies, since this study shows positive impact and relationship between South Africa’s economic growth and BRICs FDI inflows. The BRICs economies should focus on enhancing investment partnership, preventing protectionism, and promoting intra-BRICS flows. In addition, South Africa should eliminate barriers affecting business with BRICs countries. Policy makers should promote the building of new companies (for example Greenfield Investment) so that the economy of South Africa could grow and create employment. , Thesis (MA) -- Faculty of Business and Economic Sciences, Economics, 2021
- Full Text:
- Date Issued: 2021-04
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