Theses and Dissertations (Zoology and Entomology)

Permanent URI for this collectionhttp://hdl.handle.net/2263/31849

Browse

Now showing 1 - 20 of 418

Metabolic heat generation in larval masses of the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), at different stocking rates
(University of Pretoria, 2025-02) Weldon, Christopher W.; masombukajt@gmail.com; Masombuka, Thulani Jack
The increasing global population, expected to surpass nine billion by the mid-21st century, necessitates innovative solutions for sustainable food and feed production. Insect larvae, specifically of the black soldier fly (Hermetia illucens), offer a promising alternative through bioconversion technology, wherein insects convert organic waste into valuable products like protein-rich animal feed, human food, and by-products such as frass and chitin. This study investigates the impact of stocking rate and temperature on the heat accumulation, development and growth and performance of black soldier fly larvae fed on pre-consumer fruit and vegetable waste. Larvae were reared at four stocking rates (0.5, 1, 1.5, and 2 g diet per larva) and incubated at three temperatures (27.5°C, 30°C, and 32.5°C). Results showed that increasing stocking rate led to heat accumulation in larval aggregations, which affected larval development. While survival rates were highest at 32.5°C with 0.5 g/larva (44.95%), weight gain was greatest at 30°C. Larval length was highest at 27.5°C. Bioconversion efficiency peaked at 45% with a stocking rate of 0.5 g/larva. Waste reduction efficiency remained consistently high across treatments, demonstrating the adaptability of H. illucens larvae for bioconversion in varied conditions. This research highlights the potential of black soldier fly larvae as a sustainable method for waste management and resource conversion, supporting both food and feed production.
Assessing occupancy of mammals in the Waterberg Mountain Catchment area across spatial scales
(University of Pretoria, 2024-11-19) Keith, Mark; Marshal, Jason P.; u22881027@tuks.ac.za; Naleba, Rodney
The on-going global decline of large mammals mainly due to anthropogenic activities, necessitates enhanced management and conservation efforts. Hence, there is a considerable need for monitoring ecological estimates such as mammal occupancy and distribution in space and time. Monitoring the impact of factors responsible for mammal occupancy and distribution is equally important. Additionally, the scale at which such investigations are carried out is also key to ensure reliable outcomes for informed decision making in the management and conservation of mammals. The Waterberg Mountain catchment (WMC) is situated in the Limpopo province of South Africa. This a very biodiverse area, however, few comprehensive studies on the biological diversity and associated aspects from this area have been carried out. This area consists of several small, fenced wildlife properties. As such, the main activity in the area is eco-tourism (wildlife-based) for economic purposes as well as contributing to conservation. The small, fenced, and the isolated nature of the wildlife properties in the WMC necessitates a considerable level of human intervention in the management of mammals and their environments. I used camera trap data collected between December 2021 and April 2024 from the WMC from several wildlife properties. I analysed the data using multi-species Bayesian occupancy models, modelling mammal occurrence as a function of several site-level covariates, including distance to nearest permanent water sources, distance to roads, normalized difference vegetation index (NDVI), elevation, among others to investigate the key drivers of mammal occupancy in the WMC. Furthermore, I measured site-level covariates at multiple spatial scales to examine if variation exists in mammal occurrence patterns across scales. I also sought to compare occupancy patterns observed between managed (fenced and managed) and non-managed mammal species (free ranging with the ability to cross through fences between properties). The results generally showed that anthropogenic variables were more impactful than environmental variables in driving mammal occupancy. Moreover, deriving covariates at multiple spatial scales had an impact on the mammal occurrence patterns observed. Also, differences between mammal occupancy responses were observed between managed and non-managed mammal species. These general observations were made even though most of the results were not statistically significant (using 95% confidence intervals). These findings highlight the importance of anthropogenic infrastructures including roads, buildings, and fences on mammal occurrence and space use patterns within small, fenced wildlife properties. In addition, the results suggest that scale should always be considered when designing species-environment relationship studies. Finally, the results highlight the importance of the environmental context (small, fenced wildlife properties) on mammals’ occurrence patterns and distribution, which in turn influences mammal ecology.
Impacts of maize cropping systems on soil microbiome phytochemistry and trophic interactions between the fall armyworm, Spodoptera frugiperda (J. E. Smith) and its endoparasitoid Cotesia icipe (Fernandez-Triana & Fiaboe)
(University of Pretoria, 2025-02-14) Yusuf, Abdullahi Ahmed; Mutyambai, Daniel Munyao; Khamis, Fathiya Mbarak; AJALLOH@ICIPE.ORG; Jalloh, Abdul A.
Intensification of staple crop production with synthetic chemical inputs has contributed to negative environmental impacts. Ecological intensification, using diverse maize-cropping systems, has the potential to reverse these detrimental effects and sustainably improve crop productivity. However, the influence of these diverse maize-cropping systems on soil physicochemical properties, the soil and maize-root microbiome, and subsequent plant-insect interactions has not been clearly understood. Diversified maize-cropping systems, such as push-pull cropping systems and maize edible-legume intercropping (MLI) systems, are known to enhance plant defence mechanisms, reducing susceptibility to invasive pests like the fall armyworm (FAW, Spodoptera frugiperda J. E. Smith). This polyphagous pest, originating from the Americas, has become a global concern with its invasion into Africa and subsequent spread worldwide, targeting over 353 host plant species, primarily maize and sorghum, staple crops for most African communities. Despite the widespread damage caused by S. frugiperda, limited research has focused on understanding the influence and mechanisms of diverse maize-cropping systems soil legacy on inducing resistance to pests. Therefore, the goal of this study was to determine the effects of different types of maize-cropping systems (push-pull, MLI, and maize-monoculture) on soil health (the soil's physical and chemical properties), the microbiome (the rhizospheric soil, and the bacterial and fungal communities that live in the roots of the maize plants), and the plant's resistance to damage by the S. frugiperda. This encompassed both direct effects, such as reduced S. frugiperda neonate feeding and larval development, and indirect effects, such as the attraction of the S. frugiperda endoparasitoid, Cotesia icipe (Fernandez-Triana & Fiaboe). Chapter one of this thesis briefly introduces S. frugiperda and emphasises the significance of soil physicochemical properties and the microbiome in diversified maize-cropping systems. It discusses the importance of studying tritrophic interactions in maize-cropping systems, investigated the influence of soil microbiomes on plant-insect interactions, and examined the role of the endoparasitoid, C. icipe in pest management. The chapter also reviews available control methods, suitable farming practices for enhancing soil and plant health, and effective pest management strategies. Finally, it outlines the rationale and objectives of the study. Chapter two outlines the field sampling procedures used on long-term push-pull cropping system farms. The soil physicochemical properties and microbiomes were analyzed using the Bouyoucos hydrometer method and the MiSeq Illumina sequencing platform. The goal was to understand the impact of long-term push-pull cropping systems on the physicochemical properties of soil, rhizospheric, soil and maize-root microbiomes. Soil from push-pull cropping systems had higher levels of pH, electrical conductivity, nitrogen, organic carbon, potassium, phosphorus, calcium, magnesium, and exchangeable acidity, among other parameters, compared to soil from conventional maize-monoculture cropping systems. The study compares the microbiomes relative abundance, diversity, and functional protein pathways with conventional maize-monoculture cropping systems. This chapter emphasizes the less-known belowground interactions within the push-pull, revealing its significance in harboring ecologically important microbial groups that improve soil fertility, decomposition, nutrient cycling, and plant protection compared to maize-monoculture cropping systems. Chapter three examines the impact of crop mixtures, particularly MLI systems, on belowground microbial communities and soil physicochemical properties in maize-cropping systems. By comparing the maize-monoculture cropping system with four different MLI systems, it shows that crop mixtures have a big effect on the rhizospheric soil and the microbial community restructuring around maize-roots. They also facilitate the growth of beneficial fungal and bacterial populations, significantly contributing to agrobiodiversity and belowground ecological services. Chapter four presents the findings on the impact of MLI in comparison with conventional maize-monoculture cropping systems, on soil legacies, maize growth, and the direct resistance of maize plants to S. frugiperda. The chapter includes details on field sampling and soil physicochemical properties, maize plant growth parameters evaluation, and S. frugiperda neonate feeding and larval development. The findings of this study reveals that soil-conditioned by MLI systems enhances nutrient levels and maize growth while reducing S. frugiperda neonates feeding and larval development. Hence, this chapter underscores the positive influence of soil-conditioned by MLI systems on maize plant growth, soil health, and S. frugiperda management. Chapter five discusses how long-term push-pull cropping systems alter the soil and affect plant-soil feedback. It focuses on maize phytochemical profiles, volatile-mediated interactions in plant-insect relationships, and plant growth parameters. The study scrutinizes the behavioural reactions of the S. frugiperda endoparasitoid, C. icipe, to the alterations in volatile profiles resulting from push-pull soil-conditioning, in contrast to conventional maize-monoculture cropping systems. Maize plants grown in soil-conditioned by push-pull had higher soil physicochemical properties, plant biomass, and growth rate. Consequently, S. frugiperda neonates fed less on leaf tissues from soil-conditioned by push-pull in comparison to maize grown in soil-conditioned by maize-monoculture cropping systems. In quantitative and qualitative terms, diverse volatiles were observed in maize plants grown in soil-conditioned by push-pull cropping systems compared to maize-monoculture cropping systems. The volatiles emitted by maize plants grown in soil-conditioned by push-pull cropping systems were significantly more attractive to C. icipe than those emitted by maize plants grown in maize-monoculture cropping systems. Chapter six discusses and concludes the thesis, provides a summary of the study's key findings, explores practical applications of the findings, and offered recommendations for future research endeavors.
Malaria vector composition and insecticide resistance in Vhembe district, a high disease burden region of South Africa
(University of Pretoria, 2025-02) Riddin, Megan A.; Bastos, Armanda D.S.; u21847585@tuks.co.za; Kachali, Kondwani
South Africa’s malaria endemic provinces (Limpopo, Mpumalanga & KwaZulu-Natal) continue to face residual malaria transmission that is partly attributed to outdoor biting and resting Anopheles species. This reduces effectiveness of control interventions as they mostly target indoor vector species. Limpopo Province remains the most affected region in the country, carrying the highest disease burden, particularly in the north-eastern Vhembe district. However, the factors sustaining residual transmission in the area remain unknown. Vectors responsible for transmitting malaria and other potential secondary species have been reported in the area, but in low numbers, as has the presence of species implicated in malaria transmission in other African countries. The role of vectors and other factors, including insecticide resistance, in the persistence of residual malaria remain to be determined. Therefore, this study investigated species composition, feeding preference and insecticide resistant status in mosquitoes from Vhembe, towards understanding the cause of the persistent and residual malaria. Anopheles mosquitoes were collected in Bende Mutale, Tshivaloni, and Gwakwani, some of the areas in the Vhembe district, Limpopo Province, with the highest malaria burden. Mosquitoes were collected using carbon dioxide- and animal-baited traps, dippers and sweep nets over four collection events during the 2022-2023 and 2023-2024 malaria season. Species were morphologically identified to species level, with those belonging to the An. gambiae complex and Anopheles funestus group being identified by species-specific polymerase chain reaction (PCR). For those specimens that could not be identified morphologically, amplification and sequencing of the cytochrome oxidase subunit 1 (COI) barcoding region was performed. Insecticide susceptibility testing was carried out on Anopheles mosquitoes using standard WHO tube bioassays, testing against DDT, deltamethrin, bendiocarb and malathion. PCR and sequencing were used to investigate knockdown resistance (kdr) mutations using a typing approach. Finally, host preference was investigated through bloodmeal analysis on wild-caught blood fed females using PCR and sequencing of the cytochrome b (cyt b) gene. A total of 6,134 Anopheles specimens were collected of which 4,772 were used for insecticide susceptibility testing. Species composition assessment (Chapter 2) revealed that Anopheles gambiae s.l. (n=2,160) comprised of three sibling species in Vhembe: An. arabiensis, An. merus and An. quadriannulatus. The 357 An. funestus s.l. collected consisted of An. rivulorum-like, An. rivulorum, An. leesoni and An. vaneedeni. Other species collected included An. coustani, An. rufipes, An. pretoriensis, An. listeri, An. nili and An. gibbinsi. Nine Anopheles spp could not be assigned to species based on COI sequencing. Insecticide susceptibility testing (Chapter 3) detected potential resistance to bendiocarb and deltamethrin in An. quadriannulatus and An. rivulorum, respectively. Resistance to DDT, deltamethrin and bendiocarb was detected in An. coustani, An. rufipes, and An. pretoriensis. Full insecticide susceptibility to all insecticides was reported in An. arabiensis, An. merus, An. vaneedeni, An. rivulorum-like and An. leesoni. The sodium channel mutation associated with kdr resistance was not detected in any of the An. gambiae s.l. specimens tested. Host-specificity assessed through bloodmeal analyses (Chapter 4) revealed that An. quadriannulatus and An. pretoriensis favoured cattle and goats. Comparative analysis of two cyt b assays confirmed that both amplify mosquito vector DNA in the absence of bloodmeal DNA of adequate integrity. The results of this study support continued entomological monitoring to further investigate the roles of these species in malaria transmission and to monitor insecticide resistance in these populations. Successful implementation of targeted interventions relies on research evidence to effectively reduce vector and malaria burden.
The mechanisms of socially induced infertility of the highveld mole-rat (Cryptomys hottentotus pretoriae)
(University of Pretoria, 2024-11) Bennett, Nigel Charles; Hart, Daniel William; Oosthuizen, Carel ; u18112537@tuks.co.za; De Wet-Marais, Christiaan
This thesis explores the intricate mechanisms underlying reproductive suppression and queen succession in the highveld mole-rat (Cryptomys hottentotus pretoriae), a cooperatively breeding social rodent within the family Bathyergidae. In these colonies, a dominant breeding female (the queen) exclusively monopolises reproduction, while subordinate members of both sexes are hysiologically suppressed through a complex interplay of social, hormonal, and ecological factors. Central to this hierarchy and suppression is prolactin (PRL), a key hormone in mammalian reproduction that regulates energy allocation and social behaviours, enforcing infertility among non breeding females (NBFs) and ensuring colony stability. Field and laboratory experiments revealed that PRL levels are modulated by ecological and seasonal influences. During the dry season, elevated PRL levels maintain reproductive suppression, possibly through restricted feeding of subordinates by dominant breeders. In contrast, the wet season, marked by increased food availability, triggers a reduction in PRL levels, enabling partial reproductive activation in NBFs and facilitating dispersal opportunities. Experiments involving forced dispersal and sucrose supplementation demonstrated a direct link between decreased PRL levels, improved energy balance, and reproductive activation. However, the dopamine agonist bromocriptine, typically effective in lowering PRL, failed to do so in highveld mole-rats, suggesting an evolutionary resistance to dopaminergic regulation in the dopamine-prolactin (DA-PRL) axis. The findings underscore the centrality of PRL in maintaining socially induced infertility, shaped by energy dynamics and environmental conditions. This strategy is critical for reproductive suppression in cooperative breeders, balancing ecological pressures, genetic risks, and social stability. Among highveld mole-rats, PRL mediated suppression not only sustains the reproductive hierarchy, but also facilitates colony cohesion. Within intact colonies, PRL levels varied significantly among NBFs, with heavier females—potential "beta queens"—exhibiting lower PRL levels and partial reproductive activation. Upon queen removal, females with the lowest PRL levels were most likely to succeed to new queen status (regardless of their relatedness to the breeding male), supported by elevated testosterone levels that enabled the aggression necessary to dominate rivals. Once the new queen was established, her testosterone levels subsided, reducing prolonged aggression, and stabilising the colony. This chapter also found a minimal influence of genetic relatedness on queen succession, emphasising hormonal regulation over incest avoidance. Yet, despite their tolerance for inbreeding, highveld mole-rats showed a preference for unrelated males when available, highlighting a secondary role for genetic diversity in mate selection. The thesis demonstrates how PRL-mediated physiological suppression underpins reproductive hierarchies, illustrating the delicate balance between ecological, hormonal, and social factors that shape reproductive strategies in inbreeding-tolerant species. In conclusion, this work provides valuable insights into the evolutionary adaptations and hormonal mechanisms that maintain reproductive hierarchies in cooperative breeders. The findings have significant implications for understanding how environmental and social factors influence reproductive dynamics, contributing to a broader knowledge of behavioural ecology and the evolution of sociality in mammals.
Bat diversity in the Waterberg mountain catchment, Limpopo province South Africa : patterns and drivers
(University of Pretoria, 2025-02) Keith, Mark; Somers, Michael J.; Parker, Daniel Matthew; tracy.basch@tuks.co.za; Basch, Tracy
The Waterberg Mountain Catchment (WMC) in Limpopo, South Africa, is an important region due to its diverse environments. A large area of the WMC was designated as a United Nations Educational, Scientific and Cultural Organization (UNESCO) Biosphere Reserve in 2001. The WMC spans approximately 650000 hectares and includes a variety of vegetation types and geological formations. There have been shifts in land-use within the WMC, with a recent rise in wildlife-based activities, such as eco-tourism, hunting, and wildlife production. While tourism is often seen as beneficial for biodiversity conservation, it can sometimes lead to decreased diversity due to habitat loss from infrastructure development and the introduction of non-native species. Agriculture, including crop production and livestock farming, is a significant influence in the region, affecting local wildlife by reducing potential habitat and resources, which can lead to increased interspecific competition. The adverse effects of land-use changes impact volant and non-volant mammals differently, as the sustained flight capabilities of volant species enable them to overcome barriers between areas with enough resources to sustain them. Bats are categorised into foraging guilds based on their morphology and behavioural traits. These guilds include open-space foragers, edge-space foragers, and clutter-space foragers, each adapted to different environmental conditions. By using these foraging guilds and species richness, I analysed how different land-use types, and other factors of environmental and anthropogenic drivers in the WMC potentially influenced bat diversity and assemblages in the Waterberg. I further investigated how the various factors might affect bat diversity and relative call activity in the WMC to different extents. By analysing bat assemblages in relation to these factors at various scales (30 m, one km and five km), I aimed to provide insights into how these measures at the scales could influence/affect richness and relative call activity. My key question was what species of bat are present in the WMC and what drivers (anthropogenic or natural) might have influenced the presence or absence of various species and the abundances of those species present. I collected data by active capture and release sampling to manually identify bat species with the use of mist nets, harp traps, and by passively recording bat call data using audio recorders. I analysed my processed call data to determine species richness and relative call activity (using Miller’s Index). Generalised linear mixed models were run using variables measured from satellite imagery and QGIS to determine what drivers influenced distribution. I found that bat species richness was relatively homogeneous across the WMC. I recorded 23 bat species, consistent with historical records of 27 species for the region. I recorded two species, Nycticeinops schlieffenii and Neoromicia anchietae, that had not previously been recorded in the area. My results showed that the foraging guilds that contributed the most to species richness were the open-space and edge-space foraging guilds. Aside from foraging guilds, I also grouped species into adapter and avoider species based on roosting habits and how well the species survive in disturbed environments. The relative call activity of adapter species (mainly free-tailed and vesper bats), compared to avoider species (such as horseshoe bats), was higher due to increased anthropogenic disturbances (such as cleared vegetation for buildings, roads, etc.). Cleared vegetation for buildings and roads etc. would result in reduced roosting sites for Rhinolophus species and other clutter-space guild species. Despite similar species richness across properties, species’ relative call activity varied, with edge-space foraging guilds notably predominant. This guild seemed to benefit from low-intensity agriculture, livestock farms, and areas with cleared vegetation. Clutter-space foragers, which are less adaptable and more sensitive to habitat fragmentation, were notably scarce throughout the WMC. Habitat heterogeneity supports species richness by offering diverse resources and roosting sites, but excessive heterogeneity can negatively impact specialized species like clutter-space foragers. While heterogeneity alone does not affect species richness, the availability of space and the degree of fragmentation do. Clutter-space foragers also had lower detection rates due to their higher frequency calls and limited roosting options in southern Africa, leading to increased interspecies competition. Clutter-space forager relative call activity was influenced by the presence of roosting sites and denser vegetation. The generalised linear mixed model results indicated that bat species richness declined with increased normalised difference vegetation index (NDVI) and vegetation complexity, while relative call activity increased with decreased clutter and distance to clutter. Despite the influence of land-use and water availability on bat populations in other studies, I did not detect an influence of these factors on species richness in my study. Small-scale, low-intensity agricultural lands were less impactful than anticipated, possibly due to seasonal activity and water sources being less limiting. Water sources in the Waterberg are more abundant, thus potentially not being limiting as it may have been in other studies. Some studies also show that agricultural properties surrounded by natural vegetation support bat richness and activity. Aside from seasonal influences, my study didn’t include insect abundance (thus food availability) which may have also influenced the results. Elevation and vegetation types were significant at the five km scale, with higher elevations and dense vegetation reducing bat relative call activity and richness. The study concluded that bat richness and relative call activity are influenced by a combination of elevation, NDVI, and distance to clutter, with broader scales (five km) providing clearer insights into distribution patterns. These factors combined would indicate that change in vegetation cover along an elevational gradient could be a driver of diversity. Thus, land-owners and property management should prioritise the maintenance of cluttered habitats to support avoider species, particularly clutter-space foragers. Research into roosting preferences and specific management of vegetation cover could increase prey relative call activity and foraging opportunities for these species. Establishing buffer zones and ecological corridors to reduce habitat fragmentation and maintaining diverse vegetation structures will help support both adapter and avoider species, contributing to the long-term survival of bat populations in the WMC and similar environments.
A risk assessment of anthropogenic activities on cetaceans in South Africa in light of the expanding oceans economy
(University of Pretoria, 2024-09) Vermeulen, Els; Purdon, Jean; u18011536@tuks.co.za; Grobler, Alannah
The unique oceanographic characteristics of the South African marine environment gives rise to high biological productivity and a wide variety of habitat types. These in turn are able to support a high diversity of marine life, including a variety of cetacean species. In addition to this, the South African marine environment provides biotic and abiotic resources which can be utilised by humans. In an effort to boost the South African economy by expanding the utilisation of its marine environment, Oceans Phakisa was launched in 2014. In light of this expansion, the interaction between marine life and the anthropogenic activities utilising ocean resources must be investigated, and potential risks must be determined. Consequently, a risk assessment of anthropogenic activities on cetaceans in the South African Exclusive Economic Zone (EEZ) was developed. In first instance, the impact of anthropogenic activities on cetacean mortalities was determined. This was done through an analysis of cetacean mortality data collated between 1969 and 2023. Most cetacean mortality records (62%) were not assigned a cause of death. However, at least 38% of cetacean mortalities were associated with an anthropogenic activity. Entanglements in bather protection nets were most frequently identified as the cause of mortalities, followed by bycatch, ship strikes, and entanglement in fishing gear. Midwater trawls were most frequently involved in bycatch incidents, while octopus and rock lobster trap fisheries were most frequently involved in fatal entanglements in fishing gear. Indo-Pacific bottlenose dolphins, Bryde’s whales, humpback whales, and dusky dolphins were frequently identified in anthropogenic related mortalities. Spatial analysis of the mortality data identified the west and south coast of South Africa as hotspots of cetacean mortalities, especially during summer months (October to March). Secondly, the risk that marine anthropogenic activities may pose to cetacean species was assessed. This was done by conducting a spatiotemporal analysis of the distribution overlap of 18 cetacean species and the spatial footprint of 9anthropogenic activities in the South African EEZ. Results indicated that all modelled cetacean distributions in the South African EEZ overlapped with at least one anthropogenic activity. Shipping activity overlapped with all cetacean distributions and may therefore pose the highest overall risk based on spatial overlap. Risso’s dolphins, minke whales, sperm whales and common dolphins were identified as the species with distributions that have a higher than 80% overlap with shipping activity. Results indicated that most cetaceans in the South African EEZ may be at risk from the effects associated with cumulative anthropogenic pressures. The west and south coasts of South Africa were identified as areas were risk to cetacean species from the effects of anthropogenic activities was highest. The results of this thesis provide a baseline analysis of risk which can be used during the development of mitigation and management strategies as well as to inform Marine Spatial Planning processes.
Oviposition dynamics and sex ratio model assumptions in pollinating fig wasps
(University of Pretoria, 2024-12) Greeff, Jacobus Maree; Van Noort, Simon; De Waal, Pam; simisom2000@gmail.com; Mnguni, Simiso Polite
This thesis investigates a few assumptions of sex allocation in fig wasps, a pivotal subject in evolutionary biology and sex ratio theory. We investigate specifically if species can be considered in isolation of one another, and if the females that share a fig, oviposit simultaneously or sequentially. In doing so the study tries to explain deviations in fig wasp sex ratios from predictions made by classical frequency-dependent selection models. As more mothers oviposit in a fig, their offspring sex ratios become less female biased as predicted, but to a lesser degree than is optimal. The adaptive adjustment is a result of the two mechanisms of sex ratio adjustment in pollinating fig wasps: a passive response due to unlaid female eggs in competitive environments, and a facultative response involving increased male egg production in the presence of co-foundresses. An information-theoretic approach allowed me to contrast different hypotheses and to conclude that the presence of heterospecifics disrupts these mechanisms, leading to maladaptive sex ratios and illustrating trade-offs between versatility and specialization. The standard sex ratio models based on local mate competition theory assumes that females oviposit simultaneous. My direct observations show that sequential oviposition is in fact more frequent than simultaneous oviposition and this can help to explain sex ratios that are too female-biased in multi-mother figs. To investigate sequentiality further, I used an Approximate Bayesian Computation approach to estimate parameters such as wasp entry probabilities, foundress longevity, and ostiole closure timing The estimated parameters suggests that sequential oviposition is very likely because figs stay open for longer than wasps stay alive.
Southern right whale (Eubalaena australis) migratory and foraging behaviour in a changing climate
(University of Pretoria, 2025-01-20) Vermeulen, Els; Vichi, Marcello; u15029507@tuks.co.za; Germishuizen, Matthew
The name “right” whale reflects the violent history of southern right whales (SRW, Eubalaena australis) since their sluggish, predictable coastal behaviour and the tendency to float when dead led to the reputation of being the “right” whales to hunt. Now, the characteristics that contributed to their near demise carry a less sinister connotation, that of being the “right” climate sentinel. Their life histories and wide-ranging migratory behaviour make SRWs ideal candidates for monitoring environmental change. SRWs are capital breeders with discrete periods in their life histories dedicated to foraging and reproduction. Therefore, females have a strong impetus to accumulate sufficient energy reserves during their foraging period to sustain them through pregnancy and calf nursing. Thus, a strong connection exists between foraging efficiency and reproductive success. Foraging efficiency is largely dictated by the environment’s ability to generate productive feeding grounds. Sea ice, for example, has a fundamental role in the life history of Antarctic krill (Euphausia superba), a key prey species for SRWs. Changes in reproductive success in SRWs may indicate climate-induced alterations in prey, such as reductions in sea ice, in their offshore feeding grounds. Following a steady period of recovery from commercial whaling, SRW populations recently began displaying signs of reduced population growth rates and reproductive failure. This prompted an in-depth assessment into potential drivers behind these changes, and their contemporary migratory and foraging behaviour. This thesis is focused on the South African population, which through annual aerial surveys has been extensively monitored since 1969. The resultant time-series of population demographic data has revealed drastic reductions in reproductive success after 2009, together with a northward shift in foraging location as indicated by stable isotopes, and a decline in maternal body condition. To better understand these changes, an assessment into patterns of satellite-derived chlorophyll and sea ice as proxies for foraging habitat quality was performed over the period of observed population-level reductions in reproductive success. This revealed substantial declines in sea ice over historically important foraging grounds for SRWs, which likely contributed to reduced availability of their main prey at high-latitudes; Antarctic krill. The thesis reports on the use of animal-borne Conductivity, Temperature and Depth instruments and dive depth recording tags in better understanding the environmental characteristics of their mid-latitude foraging grounds. Results highlighted the importance of ocean fronts, temperature and salinity in determining favourable foraging grounds. Finally, through the deployment of 26 location-only satellite tags, a comprehensive investigation into the contemporary offshore migratory and foraging behaviour of South African SRWs was performed. From these, areas of high use were identified, and the presence of foraging whales was predicted from eight environmental covariates using Random forest. This significantly increased our knowledge of SRW contemporary habitat use. The findings of this thesis highlight the strong connections between SRWs and their environment, and the vulnerability of the species to climate change and variability. This also reaffirms the utility of SRWs as the “right” sentinels for environmental change.
Foraging strategies and spatial-temporal partitioning by brown hyenas (Hyaena brunnea, Thunberg 1820) around a coastal food source: implications for conservation and ecotourism in the TsauǁKhaeb National Park, Namibia
(University of Pretoria, 2024-11-16) Somers, Michael J.; Wiesel, Ingrid; marie.lemerle@strandwolf.org; Lemerle, Marie Anna
The coastal ecosystem of the TsauǁKhaeb National Park in Namibia serves as an important foraging ground for both brown hyenas (Hyaena brunnea) and black-backed jackals (Lupulella mesomelas). The presence of breeding colonies of Cape fur seals (Arctocephalus pusillus pusillus) provides a year-round food source, with hunting opportunities for the local carnivores. At the Baker’s Bay seal colony, brown hyenas display unique behavioural patterns around a concentrated food source. This thesis aims to investigate the temporal activity patterns, foraging behaviours, movement strategies, and human-wildlife interactions of brown hyenas in this unique context, providing insights that are essential for sustainable wildlife management and ecotourism development. This study was conducted at the Baker’s Bay seal colony from November 2020 to December 2023. A combination of direct behavioural observations and camera trap data were used to analyse the activity patterns of brown hyenas and black-backed jackals at the seal colony. Brown hyenas exhibited individually distinct activity patterns, ranging from nocturnal to diurnal. During diurnal observations, brown hyenas were most active around midday, while black-backed jackal numbers peaked around dawn and dusk. Carnivore activity was influenced by weather conditions. Additionally, brown hyenas showed a preference for fresh carcasses at the seal colony, and displayed surplus killing and caching behaviours of seal pups. Male brown hyenas hunted more frequently, whereas females demonstrated greater efficiency. The analysis of movement patterns using satellite GPS collars revealed that coastal brown hyenas had smaller home ranges and less varied diets compared to their inland counterparts, emphasising the importance of seal colonies as primary foraging sites. Collared brown hyenas exhibited significant overlap in their home ranges around key resources, leading to territorial disputes and highlighting the complex social dynamics among brown hyena clans. The potential for ecotourism development at Baker’s Bay was also explored. Brown hyenas were sensitive to movements such as people walking or vehicles driving, and human disturbances altered their foraging behaviour. Recommendations for sustainable tourism include controlled visitor access, use of infrastructure to minimise disturbance, and continuous monitoring of brown hyena activity patterns to ensure the long-term sustainability of ecotourism in the area. Overall, this study underscores the importance of balancing tourism with conservation efforts. The results provide insights into the behavioural ecology of brown hyenas in a coastal ecosystem, and highlight the importance of developing conservation strategies that consider the unique adaptations of coastal predators and the impact of human activities. By proposing guidelines and recommendations for policymakers and tour operators, this research contributes to the establishment of responsible and sustainable wildlife tourism practices, ensuring the conservation of this unique ecological hotspot.
Evaluation of stable isotope ratios of historical and modern samples of invasive and indigenous murid rodents, with respect to historical urbanization in Gauteng Province, South Africa
(University of Pretoria, 2024-07) Chimimba, Christian Timothy; Hall, Grant; u16125119@tuks.co.za; Engelbrecht, Armand
Natural history traits such as sex and ontogeny (i.e., age), environmental factors such as season, habitat, and time of sampling, and the nature and extent of urbanization may influence the trophic ecology of rodents. The current study used stable isotope analysis (SIA) of modern and historical samples to: 1) investigate the potential influence of natural history traits and environmental factors that also included metrics of urbanization on carbon (δ13C) and nitrogen (δ15N) isotope ratios in murid rodents from Gauteng Province, South Africa; and 2) evaluate their potential trophic ecological shifts due to urbanization over a historical time scale. SIA was conducted on biologically inert fur samples of modern and historical samples (i.e., museum-preserved samples collected over a time scale) of three invasive (Rattus rattus, R. norvegicus and R. tanezumi) and three indigenous (Aethomys ineptus, Mastomys coucha and Otomys angoniensis) murid rodents. Generalized linear models (GLM), analysis of variance (ANOVA) and Tukey’s post-hoc analyses showed that sex, age, and sampling year had minimal impact on δ13C and δ15N isotope ratios, but not sampling locality and season. These results were supported by the analysis of percentage trophic overlaps based on sample size-corrected standard ellipse areas (SEAc). Collectively, these results suggest that in the last century, short-term seasonal fluctuations accounted for a larger proportion of isotopic variation than long-term environmental changes. The results also showed that qualitative categorical land use data as a proxy for urbanization did not adequately account for changes in rodent isotope ratios. Consequently, an attempt was made to identify quantifiable potential sources of short-term variation in δ13C and δ15N stable isotope ratios in these rodents. The identified quantitative variables included monthly median temperature and monthly total rainfall as short-term metrics of environmental change and Normalized Difference Vegetation Index (NDVI) as a metric for vegetation cover and impervious surface area (ISA), both as proxies for urbanization over a historical time scale. The analyses found that both metrics of short-term environmental factors and proxies of urbanization had no impact on δ13C ratios in any of the three invasive and three indigenous murid rodent species investigated, while δ15N ratios of the insectivorous indigenous A. ineptus and M. coucha were found to be influenced by monthly median temperature and impervious surface area. Overall, the largest %SSQs were due to error (i.e., residual), suggesting that apart from the metrics analysed and the interaction between them, there may be other unexplained components that are also responsible for the variation. These results suggest that the murid rodent populations investigated may be shielded from the negative impacts of short-term environmental factors and urbanization through the availability of excess food resources in one of the most urbanized landscapes in South Africa. This has implications on potential knock-on effects in other aspects of the behaviour and ecology of these rodents that may represent an urgent direction of focus for future research initiatives. These results highlight the potential impact of urban landscapes on the trophic ecology of invasive and indigenous murid rodents and their negative impacts on the conservation of other threatened species within urban settings.
Distribution and phenotypic population structure of the tsetse flies Glossina morsitans morsitans Westwood and Glossina morsitans centralis Machado in Zambia
(University of Pretoria, 2024-11) Sole, Catherine L. ; Pirk, Christian Walter Werner; Yusuf, Abdullahi Ahmed; u19395605@tuks.co.za; Muyobela, Jackson
Glossina morsitans s.l. is an efficient vector of African trypanosomiasis, a debilitating and fatal disease of humans and livestock. This study aimed at investigating the current distribution and phenotypic population structure of G. m. centralis Machado and G. m. morsitans Westwood to inform effective vector management strategies in Zambia. To achieve these objectives, the study also evaluating a vehicle-mounted sticky trap (VST) for effective and rapid sampling of G. morsitans over large geographic areas. Randomised block design experiments were used to establish the optimal design of VST. An extensive VST based tsetse survey was then conducted in all tsetse belts in Zambia. The occurrence records obtained from this survey were used to model the distribution of G. m. centralis and G. m. morsitans using a Maxent species distribution model. Landmark-based wing geometric morphometrics was undertaken to investigate the population-level phenotypic variation of the two subspecies. There were no significant differences in catch indices of VST constructed using an all-blue, all-black and 1:1 blue-black panel. Overall, the VST oriented in-line and baited with butanone and 1-octen-3-ol, caught 2.42 and 2.60 times more G. m. centralis and G. m. morsitans respectively, than the standard mobile trapping device, the black-screen fly round. The VST survey captured a total of 15,602 flies with G. m. morsitans (58%) and G. m. centralis (39%) being the most abundant. The predicted potential distribution for G. m. centralis was 80,863 km2 while that of G. m. morsitans was 70,490 km2 representing a 47 and 29% reduction compared to their historical distributions, respectively. Significant differences in wing centroid size and shape were observed between G. morsitans sexes, subspecies and sample locations within each subspecies range. The populations of G. morsitans were found to exhibit significant population-level variation in fly size and wing shape which suggests high levels of population structuring. The main drivers of this structuring could be random genetic drift in G. m. centralis demes and local adaptation to environmental conditions in G. m. morsitans populations.
Development of effective biorationals for sustainable management of the invasive South American tomato leafminer Phthorimaea absoluta Meyrick (Lepidoptera: Gelechiidae)
(University of Pretoria, 2024-09) Torto, Baldwyn; Yusuf, Abdullahi Ahmed; u21831409@tuks.co.za; Adams, Bashiru
The tomato leafminer, Phthorimaea absoluta Meyrick (Lepidoptera: Gelechiidae) formerly known as Tuta absoluta is an invasive pest of Solanaceous crops with preferences for cultivated tomato (Solanum lycopersicum) where it is a major pest. Herbivory by P. absoluta larvae causes 80-100% yield losses in unprotected fields, with an estimated mean seasonal production loss of at least 114,000 tonnes, translating to about US$ 59.3 million in economic losses in Kenya. Synthetic chemical control has been the mainstay in managing the moth, with limited success because of the cryptic nature of the feeding larvae, the rapid evolution of resistant populations of the moth, and more importantly the negative effect of synthetic chemicals on the environment and non-target organisms. Hence, there is a global demand for more eco-friendly alternatives such as using biorationals to control the moth. Using behavioural assays, chemical analysis, and field trials, behaviour-modifying compounds that mediate the interaction of host, non-host plants, P. absoluta, and two native natural enemies associated with the pest including the generalist mirid predator Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) and the larval parasitoid Stenomesius japonicus (Ashmead) (Hymenoptera: Eulophidae) were identified. The mirid predator N. tenuis is zoophytophagous and may become a pest in the absence of prey by feeding on the tomato plant. The results from these studies revealed that terpenes from constitutive volatiles of host plants such as tomato and nightshade and some selected non-host Asteraceae plants including marigold (Tagetes minuta) and blackjack (Bidens pilosa) elicit significant behavioural responses in the moth and the associated natural enemies. Additionally, terpenes and green leaf volatiles (GLVs) from the predator N. tenuis-induced host plant defense volatiles influence the tritrophic interaction between host plants, P. absoluta, N. tenuis, and S. japonicus. Field trials also showed that combining the sex pheromones (1-octanol and hexyl hexanoate) identified from the Kenyan population of N. tenuis with specific visual cues such as red and white delta traps can be used to suppress both P. absoluta and N. tenuis populations, respectively in a tomato field. Overall, these studies identified different behaviour-modifying chemicals that can be developed into effective biorationals for the sustainable management of P. absoluta and the predator N. tenuis when it becomes a pest.
Population and individual life history consequences of polygyny in male southern elephant seals
(University of Pretoria, 2019-11) De Bruyn, P.J. Nico; Oosthuizen, W.C. (Wessel Christiaan); kyle.john.lloyd@gmail.com; Lloyd, Kyle John
Our understanding of polygynous life history is biased towards females. Few studies investigate the processes governing male life history because of the difficulty in measuring male reproductive effort, and because population growth is thought to be limited only by females. Therefore, clarity is needed on the drivers and predictors of polygynous male life history and the long-term consequences this has for male fitness. My thesis achieves this overall aim by answering specific questions about the life history of male southern elephant seals at Marion Island using a 34-year mark-recapture dataset. The male elephant seal served as a model organism to investigate the most important life stages of polygynous males in general. For pre-breeders that survived their first year of life, individual heterogeneity in survival probabilities was expressed from age 2. Males born in years with relatively few pups were more likely to be robust in quality than males born in years with many pups. Survival probabilities of robust individuals and the population average became more similar as pre-breeders aged, suggesting that frail individuals were preferentially removed from the population during development. Therefore, the majority of pre-breeders that survived to breed successfully were robust in quality. Pre-breeder recruitment probabilities increased with age. In addition, pre-breeders of the same age often recruited as first-time subordinate breeders than as first-time dominant breeders. First-time subordinate breeders started recruiting from a younger age than first-time dominant breeders. Males likely need time to socially mature or require some breeding experience to outcompete older breeders. Pre-breeders expressed individual heterogeneity in recruitment probabilities, with robust individuals (i.e. higher survival) being more likely to recruit than frail individuals (i.e. lower survival). This supports the individual quality theory, which predicts that life-history traits are positively, rather than negatively, correlated. Pre-breeders born during low pup production years generally recruited at younger ages than pre-breeder born during high pup production years. Males attending breeding events did not suffer lower survival probabilities than same aged males that were still pre-breeders, suggesting that there was no reproductive cost for attending breeding events for early recruits. However, all males attending breeding events experienced actuarial senescence from recruitment age, with subordinate males suffering higher baseline mortalities. Given that this coincided with breeding improvement (the probability of becoming dominant), males appear to pay a reproductive cost for attempting to obtain dominance. When comparing survival probabilities between individual dominant males, there was also a reproductive cost for breeding successfully that accumulated with age. Males that were dominant at beaches with above average harem sizes accumulated higher reproductive costs than males that were dominant at beaches with below average harem sizes. Nevertheless, dominant males still maintained higher survival probabilities than subordinate males of the same age. Therefore, individual quality (inferred from breeding state) may play an important role in modifying resource allocation trade-offs between reproduction and survival. Future breeding success (measured as social status) increased with age for both subordinate and dominant males, but dominant males were more likely to remain dominant than subordinate males were in obtaining dominance. This apparent improvement in breeding success with age was predicted by birth cohort size, again suggesting that males born into cohorts with few conspecifics performed better as adults. In conclusion, I provide support for several population theories and show how they shaped male elephant seal demographics from birth to death. My findings provide valuable insight into the drivers and predictors of male life history in a highly polygynous breeding system.
Phenotypic and genotypic sources of variation in the thermal physiology of a passerine bird
(University of Pretoria, 2020-01) McKechnie, Andrew E.; noakesmatthewj@gmail.com; Noakes, Matthew Jason
There is considerable variation in avian thermal physiology, with traits such as metabolic rates correlated with climate at both inter- and intraspecific levels. However, it is often unclear whether these correlations result from genotypic adaptation, developmental plasticity or phenotypic flexibility. Seasonal acclimatization is a frequently cited example of phenotypic flexibility, with small, temperate-zone birds typically increasing metabolic rates in response to low winter air temperatures (Ta). Recent studies suggest considerable variation in patterns of seasonal acclimatization in birds inhabiting lower latitudes with milder winters, with variation also reported among populations of subtropical species such as the white-browed sparrow-weaver (Plocepasser mahali). To gain insights into the sources of intraspecific variation, I investigated phenotypic flexibility in the thermal physiology of Afrotropical passerine birds, using sparrow-weavers as a model species. I measured seasonal variation in basal metabolic rate (BMR) and summit metabolism (Msum) over a four-year period in arid-zone populations of sparrow-weavers and scaly-feathered weavers (Sporopipes squamifrons; chapter 1). Patterns of acclimatization varied substantially among years in both species, for example, sparrow-weaver BMR ranged from ~ 20 % lower to 68 % higher during winter compared to summer. In contrast to higher-latitude species, interannual metabolic variation was never related to minimum Ta or enhanced cold tolerance, but metabolic rates were significantly lower in seasons with lower food abundance. I also investigated seasonal changes in the body composition of sparrow-weavers, focusing on traits commonly correlated with BMR and Msum in temperate-zone birds (chapter 2). As expected, a lack of seasonal variation in BMR during the study period was associated with no significant variation in the dry mass of digestive and excretory organs. However, despite significant winter increases in pectoral muscle (~ 9 % higher; primary muscle for avian shivering thermogenesis) and heart mass (~ 18 % higher), there was a winter decrease in Msum. These findings support the idea that factors other than enhanced cold tolerance drive patterns of metabolic variation in subtropical birds. I used short-term (~ 30 days) thermal acclimation experiments to investigate whether phenotypic flexibility in thermoregulatory responses of sparrow-weaver varies among populations across a climatic gradient (~ 8 °C and 11 °C in mean daily winter minimum and summer maximum Ta respectively). I measured BMR and Msum after acclimating individuals to one of three acclimation Ta (Taccl) treatments (5 °C, 15 °C or 35 °C; chapter 3). There was ~ 12 % lower BMR and 25 % lower evaporative water loss in birds at the hottest Taccl compared to cooler treatments, with no interpopulation variation after acclimation (i.e., similar reaction norms). In contrast to the findings of most studies on temperate-zone birds, Msum did not vary with Taccl regardless of population. I also investigated flexibility in heat tolerance and evaporative cooling capacity of sparrow-weavers, measuring their ability to handle high Ta (~ 38 °C to 54 °C) after acclimation to one of three treatments (day-time Taccl = 30 °C, 36 °C or 42 °C; chapter 4). Birds at the hottest Taccl coped better with high Ta than those at milder Taccl, maintaining lower body temperatures and reaching Ta ≈ 2 °C higher before the onset of severe hyperthermia. There was no variation among populations after acclimation, suggesting similar reaction norms for heat tolerance and evaporative cooling capacity. These findings suggest previously documented interpopulation differences in sparrow-weaver thermal physiology is largely the result of phenotypic flexibility rather than local adaptation. In conclusion, I found considerable flexibility in the thermal physiology of an Afrotropical passerine bird, both within and among populations. My data support the idea that enhancing winter cold tolerance is less important in subtropical birds compared to higher-latitude species. Moreover, similar thermoregulatory reaction norms among populations highlights the importance of phenotypic flexibility as a source of variation in avian physiology.
Monitoring of large carnivores in Botswana for conservation management
(University of Pretoria, 2019-10) Somers, Michael J.; christiaan.winterbach@gmail.com; Winterbach, Christiaan Willem
Assessing the range, population size and trend of large carnivores are required for conservation management at global to local scales. Survey techniques should be precise with low bias, detect population trends and cover large areas efficiently. Track surveys may be used to monitor populations of lion (Panthera leo), leopard (Panthera pardus), spotted hyaena (Crocuta crocuta), brown hyaena (Parahyaena brunnea), cheetah (Acinonyx jubatus) and African wild dog (Lycaon pictus) in Botswana. Call up surveys is an alternative to survey lion and spotted hyaena. I recalibrated the published relationships between track density and true density. Linear regression through the origin was justified over linear regression with intercept for all models tested. Models through the origin fitted better and Akaike Information Criteria showed that these models were more robust. A review of the track survey method clarified ambiguous terminology and inappropriate analyses of data. This allows others to replicate track surveys in a way that improves inter-survey comparisons of results. I calculated species-specific calibrations to estimate confidence intervals of track densities from track incidence frequencies, and thus carnivore densities, for the entire southern African large carnivore guild. Calibration of carnivore response is required to estimate density from call up surveys. There correlation between the mean number of lions per calling station and reference density was significant (P < 0.05). Response probability did not differ by sex and age among surveys (call duration 90 minutes). Site-specific calibrations performed better than published calibrations. Call up surveys are unlikely to detect population trends in the Okavango Delta due to the high coefficient of variation (>200%). I collated data from various sources and conducted track surveys to assess brown hyaena distribution and density across land uses in Botswana. Density ranged from 0 brown hyaena / 100 km² in parts of northern Botswana, to 2.94 (2.16–3.71) brown hyaena / 100 km² in the southern Central Kalahari Game Reserve. The estimated brown hyaena population is 4642 (3133–5993). Agricultural land in Botswana is important to link populations in South Africa, Namibia and Zimbabwe. In 2005, Botswana implemented a minimum age threshold strategy to manage sustainable trophy hunting of male lions. I evaluated tooth: pulp width and area ratios to estimate age of trophy-hunted male lions in Botswana as a post hoc monitoring of compliance (2005 – 2007) to the 6-year minimum-age threshold. I used digital radiographs of the second premolar for measurements and cementum annuli analysis to calculate reference ages. The linear regression y = 0.990 x + 2.512 (r² = 0.647), between the tooth root area: root pulp cavity area ratio (R: RPA) and reference ages < 10 years (F1, 23 = 42.244, P < 0.001), was used to estimate age from R: RPA ratios. The 95% confidence intervals of age estimates from R: RPA ratios for the reference age classes 4 - 5 years and 6 - 7 years were mutually exclusive, showing the methods ability to distinguish between animals older and younger than the minimum age threshold. Wildlife tourism can provide economic incentives for conservation. I evaluated tourism potential in the Northern Conservation Zone of Botswana, using wildlife biomass and diversity estimates from aerial survey data as indicators of tourism potential. Areas used for High Paying Low Volume tourism had significantly higher mean wildlife biomass and wildlife diversity than the areas avoided for this type of tourism. Only 22% of the Northern Conservation Zone has intermediate to high tourism potential. Tourists will have significantly better wildlife sightings in areas with high tourism potential compared to low potential areas. Although the largest part of the Northern Conservation Zone has low tourism potential, it has a high conservation value. Alternative conservation strategies should be developed to complement the economic incentive provided by wildlife-based tourism in Botswana.
Using functional genomics to provide insights into social parasitism by Cape honey bee clonal workers based on mandibular gland pheromones (Apis mellifera capensis Eschscholtz)
(University of Pretoria, 2019-04) Crewe, Robin M.; Pirk, Christian Walter Werner; Yusuf, Abdullahi Ahmed; fiona.mumoki@up.ac.za; Mumoki, Fiona Nelima
The queen mandibular gland pheromone (QMP) enables the queen to maintain reproductive dominance by inhibiting worker ovary activation and production of queen-like multi-glandular secretions. While the queen is typically able to maintain the reproductive role in most colonies, some rogue workers evade this strict control to become reproductively active. An extreme form of this evasion is seen in Apis mellifera capensis (Eschscholtz 1822) where, through a short-sighted evolutionary process, a specific invasive lineage of the A. m. capensis workers developed into facultative social parasites. These parasitic workers (A. m. capensis clones) infest susceptible honey bee colonies and develop into pseudo-queens, taking over the role of reproduction. While relatively more has been described regarding the behavioural basis accompanying reproductive parasitism, the genetic basis describing how these morphologically-worker honey bees become pseudo-queens still requires more investigation. Here, the composition of the mandibular gland secretions from young, old and field-collected (age-unspecified) A. m. capensis clones from queenright and queenless social environments was investigated and compared to the mandibular secretions of A. m. scutellata workers (a subspecies with a comparatively lower reproductive potential). Techniques in gas chromatography and functional genomics were used to investigate the chemical composition of the mandibular gland secretions and the molecular pathways involved in the biosynthesis of mandibular gland fatty acid components, respectively. In the first part of this work, it is shown that even at less than 24 hours old, queenless A. m. capensis clones show queen-like signatures in their pheromone profiles through the production of 9-HDA, the precursor to the ‘queen-substance’ 9-ODA. Using high-throughput RNA sequencing technology, about 48 differentially expressed transcripts (DEGs) directly associated with the mandibular gland pheromone biosynthetic pathway in Apis mellifera, were identified. Of these DEGs, 25 were orthologues to Cytochrome P450s, enzymes involved in the caste-specific hydroxylation of acylated stearic acid, a major regulatory point in the biosynthesis of mandibular gland fatty acids. The in-situ biosynthesis and activation of stearic acid, uncompleted β- oxidation and the oxidative conversion of 9-HDA to 9-ODA were also identified as putative points of queen-associated regulation in the multi-step biosynthetic pathway. Finally, using field-collected A. m. capensis clones, it is shown that some host queens can suppress reproductive parasitism in clones by regulating the synthesis of multiple enzymes key in the production of mandibular gland components, such as Cytochrome P450 enzymes and alcohol dehydrogenases, leading to a multi-step regulation of worker reproduction. This work contributes to our understanding of the molecular-level mechanisms related to regulation of reproductive dominance and deepens our understanding of the evolution of reproductive division of labour.
Constitutive chemical defense of Eucalyptus against herbivory by Gonipterus sp. n. 2
(University of Pretoria, 2019) Hammerbacher, Almuth; Hurley, Brett P.; Schröder, Michelle; u14029406@tuks.co.za; Joubert, Johannes Christoff
The Gonipterus scutellatus species complex Gyllenhaal, 1833 (Curculionidae, Coleoptera) is comprised of 8 cryptic species native to East Australia and Tasmania. Of these 8 species only G. platensis, G. pulverulentus and Gonipterus sp. n. 2 are invasive pests. Gonipterus sp. n. 2 was first discovered outside of its native range in 1916 in South Africa, and caused widespread defoliation of Eucalyptus trees, preferentially feeding on young leaves and new shoots. In 1926 Anaphes nitens Girault, 1928 (Hymenoptera: Mymaridae), an egg parasitoid, was discovered and released in South Africa. Anaphes nitens was historically very effective until the early 2000’s when large outbreaks of the beetle were occurring with increasing frequency. Therefore, investigations for alternative management options were initiated. Both biopesticides and pesticides were tested. However, biopesticides showed little reduction in beetle populations and pesticides are expensive and under legislative control, thus lowering accessibility and hampering large scale use, which results in inefficient control of the beetle. However, Gonipterus sp. n. 2 shows a very distinct host selection behavior, preferentially feeding on certain Eucalyptus species and not at all on others. Several studies have indicated Eucalyptus defense compounds, (such as 1,8-cineole) which may be able to repel Gonipterus sp. n. 2 and could partially explain this selective feeding behavior. Therefore, understanding these compounds which potentially mediate the feeding behavior of Gonipterus sp. n. 2 can offer an alternative control strategy for these beetles. However, this feeding preference has not been studied in depth and more research is needed to understand how these compounds can be developed into a control measure for commercial Eucalyptus plantations. Therefore, the inherent resistance mechanisms of the plant against feeding by Gonipterus sp. n. 2 should further investigated.
Temporal changes in food resource availability between two karst bat assemblages
(University of Pretoria, 2020) Keith, Mark; Seamark, Ernest; tlaishegonkoana@gmail.com; Nkoana, Tlaishego Tedson
The temporal availability of arthropods varies in response to changing quality of vegetation which is influenced by climatic conditions. Climate in the Savanna and Grassland biomes is defined by wet and dry cycles. Bats (Chiroptera) are major consumers of nocturnal flying arthropods and respond to temporal fluctuations of their arthropod prey as well as climatic conditions. My study is undertaken in two karst landscapes within two biomes, Savanna (Meletse) and Grassland (Cradle of Humankind World Heritage Site-CoH WHS). The migratory Miniopterus natalensis utilizes Madimatle cave (Meletse –Thabazimbi) for maternity roosting (October-February/March) whilst caves in the CoH WHS provide hibernacula (winter) roosts (April-September) for this population. Migration in bats has been linked to changing climatic conditions for temperate species and food availability in tropical species. The factors driving the migration of Min. natalensis population are not yet understood. The temporal changes of bat assemblages and their arthropod prey from dry to wet season climatic regimes are of interest. To test this, I collected arthropods and recorded bat echolocation calls from dry to wet season (June-February), using malaise traps and Anabat SD2 bat detectors, respectively. Different bat species are adapted to forage within different levels of vegetation clutter. Traps and bat detectors were therefore spatially placed across different levels of vegetation clutter at the study sites. Arthropods were caught, measured (size and biomass) and capture success (CS=individuals/trap-hours) were calculated monthly. An Acoustic Activity Index (AAI) of recorded bats was also used to obtain monthly relative activity. My results show that bat activity corresponds to arthropod availability on a temporal basis with wet season highs and dry season lows, at both study sites. When comparing Grassland and Savanna sites, arthropod CS was significantly higher (P<0.01) at the grassland (mean CS=0.248 ind./trap) whilst biomass was greater at the savanna site. In addition, the Grassland had higher CS with lower biomass for the arthropods Diptera and Lepidoptera, whilst the larger biomass taxa, Coleoptera and Hemiptera, had higher CS at the savanna. The frequency of larger arthropods was higher in November and corresponded with peak biomass measured that month. At Meletse, significant increases (P<0.05) for bat activity and arthropod CS were recorded in August/September (late dry season) and November (wet season). Species level bat activity increases corresponded with increases in arthropod CS and biomass. The matching between bat activity patterns and arthropod availability is important for the maternity season when pregnant females have to meet increased energy demands. Indeed, the maternity season matched with periods of highest food resources expressed as increased arthropod abundance and biomass. Greater bat activity during the maternity period places Meletse as an important food resource reservoir both supporting resident and the migratory species. As bats are major predators of several taxa of nocturnal flying arthropods amongst which are agricultural pests, the ecological and economic implications of maintaining healthy bat assemblages remain of importance. Careful and effective monitoring of bat assemblages and arthropod prey will further increase understanding of the temporal dynamics between predator activity and prey abundance within habitats. Knowledge on the effects of land-use change on habitats will develop a better understanding of impacts on species and broader ecological systems.
Drivers of leopard population dynamics in the Kruger National Park, South Africa
(University of Pretoria, 2014-08) Ferreira, Sam M.; Chimimba, Christian Timothy; nmaputla@awf.org; Maputla, Nakedi Walter
In the Kruger National Park (KNP), South Africa, five of the six extant members of the large carnivore guild: lions, Panthera leo, spotted hyaenas, Crocuta crocuta, leopards, P. pardus, cheetahs, Acynonyx jubatus, and wild dogs, Lycaon pictus, are sympatric. A priori and posteriori deductions dictate that lions maintain a balance in the top-down processes in the KNP ecosystem including population abundances and behaviour of the subordinate predators. The recent discovery of the extrinsic disease, bovine tuberculosis (bTB) caused by a bacterium Mycobacterium bovis, in lions suggests that potentially, lion population may decline. Further deductions dictate that the leopard population whereas at individual level may be affected, does not appear to be challenged by the disease. This presupposes that the balance in the top-down processes will potentially be affected. By specifically assessing how this change may affect the leopard population, two mechanisms, which in the context of the KNP are contradictory were invoked. The first mechanism is the meso-predator release hypothesis, which predicts that should the lion population decline, the leopard population would increase as a consequence. The second mechanism, niche packing hypothesis, predicts that the leopard population will not experience a change as a result of the lion population declining; it argues that leopards and lions have co-evolved and as a result have developed conflict avoidance life history, morphological and ecological patterns. Consequently, the thesis set out to investigate if these mechanisms were in effect in the KNP by: (i) designing a robust method to estimate leopard abundances; (ii) estimating leopard abundances throughout the KNP; (iii) comparing leopard abundances with abundances of other members of the large carnivore guild; and (iv) assessing how leopard movements responded to indices of resource distribution and models that predicted space use by lions. Results revealed that leopards responded to resource distribution more than in response to other carnivores and especially lions as was predicted. Accordingly, niche packing theory was selected over meso-predator release theory on the grounds that at population level leopards, at least as far as the KNP is concerned, are not affected by other carnivores. This study therefore, has direct implications on the large carnivore management in KNP. The present study suggests that the leopard population is mainly driven by resources and secondarily by lions. That means in the absence of factors such as human-induced effects, and diseases that are likely to threaten their resource base and them as a result, leopard population is likely to self-regulate in KNP.

Browse

Recent Submissions