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Utilising GIS and remote sensing to assess the impacts of the invasive Rubus cuneifolius on veld grazing capacity.
(2023) Mnikathi, Ayanda Pretty.; Kirkman, Kevin Peter.; Sibanda, Mbulisi.
This study was motivated by the heavily invasion of Rubus cuneifolius (bramble) in the Mistbelt grasslands of KwaZulu-Natal province of South Africa, particularly at Wakefield Farm. When not effectively managed, bramble invasion results in dire consequences, including the reduction of veld grazing capacity. The initial steps in managing invasive alien plants (IAPs) in rangelands involves understanding their distribution and extent. This requires a suitable satellite data with optimal temporal, spectral and spatial resolution, a task that necessitates accurate and feasible mapping of IAPs. In this regard, this study aimed to assess the utility of Sentinel-2 multispectral imager in mapping the spatial distribution of bramble and assessing its impact on veld grazing capacity. This overarching aim was addressed using two specific objectives. The first objective was to test the capabilities Sentinel-2 Multispectral Imager (MSI) in detecting and mapping bramble during the senescence period. To address this objective, four sets of spectral features (all spectral bands, mNDVI, mSR and combined inputs) and the Discriminant Analysis algorithm were used to test the utility of Sentinel-2 MSI’s in detecting bramble during the senescing stage. Inputs were tested when red edge bands were included in the analysis (inclusive bands) compared to when they were excluded from the analysis (exclusive bands). The second objective was to assess the impacts of bramble invasions on grass production, species diversity and dominance. To address this objective, grass biomass and species data we gathered and dry weight rank (DWR) and double sampling techniques were utilised. A relationship between the estimated biomass and the actual biomass was determined in the invaded and the uninvaded patches. Then, Shannon-Wiener diversity index and the Simpson’s Index were used to calculate species diversity and dominance, respectively. Results showed that bramble could be detected using Sentinel-2 MSI to an overall accuracy of 89.33% with red edge derived mNDVI being the most influential discrimination variable. Furthermore, results showed a significant relationship between the estimated and the actual biomass as well as a higher total biomass in the invaded patches. In uninvaded patches, species diversity was higher while dominance was lower and in the invaded patches species diversity was lower while dominance was higher. This study highlights that Sentinel-2 MSI's red edge bands are well-suited for discriminating invasive alien plants, particularly bramble, in rangelands during annual senescence. Additionally, it emphasizes that bramble invasion diminishes the value of rangelands by reducing the productivity of palatable grass species.
Evaluation of the larvicidal potential of Bacillus velezensis strain PHP1601 as a viable biological control agent against selected fly species.
(2024) Ramesar, Danvir Rajesh.; Hunter, Charles Haig.
Flies are one of the most abundant and prevalent insect pests posing a growing threat to various sectors of the economy. In response to this, a study was undertaken to evaluate Bacillus spp. strain PHP1601 as a candidate biocontrol agent against Lucilia cuprina larvae as a proxy for fly species of biocontrol significance. The identity of PHP1601 was confirmed as B. velezensis using MLSA and species-specific PCR. Bioassays demonstrated a larvicidal effect of cell, endospore (102 – 1010 cells/endospores g -1 ) and cell-free supernatant (1 – 30% v w -1 ) treatments on second instar larvae of L. cuprina. Studies were directed to the larvicidal effect of extracellular compounds, namely lipopeptides. Crude lipopeptide extract (CLP) was acquired using organic extraction from Landy broth. Bioassays with CLP extract (5 – 1000 μg g -1 ) resulted in a dose-dependent larvicidal response. Lipopeptides in the CLP extract were purified by TLC and characterised using UPLC ESI-TOF MS. This indicated the presence of iturin, fengycin and surfactin homologues of which, the purified surfactin fraction (Rf 0.91) was the most larvicidal. Bioassays were repeated with commercial surfactin, confirming its larvicidal potency, exhibiting an LC50 of 9.87 μg g -1 at 240 h. Larvae scent choice tests using TSB and MG bioassay medium fermented by PHP1601 showed that resulting VOCs were attractive to fly larvae, which was considered a viable trait of a fly biocontrol agent. CG-MS of the VOCs produced indicated that ketones were the dominant VOC class and, presumably, the major contributor to this larvae attraction effect. Field performance evaluation using pig manure trials demonstrated successful inhibition of several fly species of agricultural and veterinary importance using endospore treatments (105 and 1010 endospores g -1 ) of PHP1601. qPCR and REP-PCR fingerprinting confirmed that PHP1601 could grow in the manure slurries and was amiable to recovery and monitoring. Zebrafish embryo toxicity bioassays of the CLP produced by PHP1601 indicated that they achieved an LC50 of 22.77 µg ml-1, which characterised these metabolites as slightly toxic. Genome mining detected no genes associated with pathogenicity or virulence and presented no apparent pathogenic threat. The investigation demonstrated that B. velezensis PHP1601 is a viable fly biocontrol candidate and constitutes the first report of a B. velezensis antagonist of Brachycera flies.
Conservation genetics of the Hooded vulture Necrosyrtes monachus.
(2023) Le Roux, Rynhardt.; Willows-Munro, Sandi.; Van Vuuren, Bettine.; Thompson, Lindy Jane.
African vulture species have experienced rapid population declines, due to many anthropogenic threats. Hooded vultures are no exception and have experienced dramatic declines and are now listed as Critically Endangered on the IUCN Red Data list. Two subspecies of Hooded vulture have been described : Necrosyrtes monachus monachus which occurs in West Africa and Necrosyrtes monachus pileatus which occurs in East and southern Africa. The two subspecies differ in their feeding behaviour and morphology supporting the validity of the subspecies status. However, the validity of this taxonomic grouping is still being questioned. Clarifying the taxonomic status of the subspecies is important as if the two subspecies are genetically distinct then they should not be managed as a single species and current conservation policies would need to be updated. In addition, there is limited information available on many aspects of Hooded vulture life history including the factors affecting reproduction in the wild. In Chapter 2 I use microsatellite data collected from across the distributions of the two subspecies and Approximate Bayesian Computation (ABC) to test the hypothesis that the two subspecies are genetically distinct and should be elevated to separate species. In Chapter 3 I examine the genetic variation present in the South African Hooded vulture population. This population only includes 100-200 individuals and is at the edge of the southern range of the species. The conservation value of peripheral populations is debatable as these populations are often isolated and smaller with genetic drift and inbreeding leading to reduced genetic variability. In contrast, studying the genetic diversity in range-edge populations is important for understanding range shifts and adaptive capacity under climate change. These edge populations could potentially also retain unique genetic diversity which helps with the adaptation of species to different environments. Vulture colonies act as “food finding information hubs” allowing for the exchange of information regarding potential food resources. This explains, in part, the high-levels of relatedness often found within colonies as close relatives are more likely to tolerate the cost of sharing food by increasing their inclusive fitness. Hooded vultures are tree nesters with a single breeding pair per tree. In Chapter 4 I use the genetic data to test if individuals nesting close to each other are closely related and if the same individuals use the same nest over multiple years. The analyses conducted in Chapter 2 did not support the existence of the two subspecies classification, due to different demographic events experienced between the two groups. The next factor indicating that there is no subspeciation is the contemporary gene flow that is still seen between the population (m = 0.188) and the little variance seen between the two subspecies (11.9%). Structure analysis also does not support the formation of two distinct subspecies. Thus, this study supports the claim made by Mundy 2021 that it is size cline and not speciation. In Chapter 3 the genetic data did not support the hypothesis that the small South African population was genetically depauperate, instead the results show that the South African population contained similar levels of genetic diversity (Ho = 0.495) to that recorded for the Ghanaian population (Ho = 0.315) where Hooded vultures are more abundant. Levels of heterozygosity were similar to those recorded for other species of Old World vultures such as Cape Vultures (Gyps coprotheres, Ho = 0.380), and Bearded vultures (Gypaetus barbatus Ho = 0.400 – 0.480), but differed from the Griffon Vulture (Gyps fulvus Ho = 0.530 – 0.600) found in Europe. Worryingly, both populations of Hooded vultures show elevated levels of inbreeding and relatedness. The bottleneck analysis for both populations show no sign of a recent bottleneck and a normal L shaped distribution for both populations. In Chapter 4 breeding pairs were not found to reuse the same nests over multiple years. A negative correlation was seen between genetic distance and geographical distance (R2 = 0.0117; p-value = 0.012) the closer related individuals thus tend to nest further away from each other. The spatial autocorrelation shows a positive correlation between genetic and geographical distance between distance classes 8 km – 16km, 32 km – 40km and then between 88 km – 112km, but no clear support for increased relatedness between closer nesting individuals. Thus no support is seen for the formation of loose colonies to function as food finding information sharing hubs. African vultures are facing a number of challenges and most species are considered of conservation concern. Despite this limited genetic data is available for many species. This study aimed to fill this knowledge gap by generating and analysing microsatellite data for the Critically Endangered Hooded vulture to answer a number of key hypotheses. As such this study makes an important contribution towards the conservation of Hooded vultures across Africa.
Pre-release evaluation of the flea beetle Heikertingerella sp. (Coleoptera: Galerucinae: Alticini), a potential biological control agent for the invasive weed Tecoma stans L. (Bignoniaceae) in South Africa.
(2024) Madire, Lulama Gracious.; Olckers, Terence.; Simelane, David Okhi.
The root-feeding beetle Heikertingerella sp. (Coleoptera: Chrysomelidae) was introduced into quarantine in South Africa for evaluation as a biological control agent of the invasive tree Tecoma stans L. (Bignoniaceae). Larval feeding damages the roots, potentially reducing the weed’s growth and reproduction. Pre-release studies in quarantine included several aspects. Studies on the beetle’s biology and host specificity were conducted to confirm its safety for release in South Africa. The impact of varying beetle densities on plant fitness was assessed to determine its likely impact in the field. The effect of local climate on the beetle’s potential to establish throughout the weed’s range in South Africa was predicted using climate-modelling software. The interaction between Heikertingerella sp. and a leaf-feeding agent already established in South Africa was investigated. Finally, the effect of host-plant age and nutrient enhancement on mass-rearing activities was studied, to optimize beetle numbers for releases. The beetle proved host specific resulting in the granting of permission for its release in South Africa. There were significant reductions in plant growth and biomass accumulation in the beetle-exposed plants, relative to the controls, indicating that Heikertingerella sp. is sufficiently damaging. Climate matching revealed that Heikertingerella sp. is likely to perform best at coastal sites in South Africa, with the colder, more inland, areas within the weed’s range proving less suitable. The beetle proved compatible with a defoliating agent established in South Africa, with evidence of positive interactions that are likely to enhance their combined impact on the weed. Trials involving plants of varying age and nutritional enhancement revealed that 3-year-old plants, which were supplemented by either medium or high levels of fertilizer, were best suited for F1 progeny production and therefore for the mass-rearing of Heikertingerella sp. for releases. The results of this study should also benefit other countries in Africa and elsewhere in the world, where the plant is invasive.
Drug transporter expression and genetic polymorphisms in HIV endemic settings.
(2023) Zondo, Nomusa Margaret.; Archary, Derseree.; Sobia, Parveen.
Abstract available in a PDF.