Faculty of Science

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Hold your horses: the effect of play behaviour in horses (Equus caballus) under imposed stress
(University of the Witwatersrand, Johannesburg, 2024) Howard, Jodi Anne; Pillay, N.
In animals, stress is inevitable, often resulting in behavioural and physiological responses to stressors. Due to the negative connotation of stress and positive connotation of play behaviour, stress and play are concepts not often coupled in research. A few studies have shown a negative association between play and stress whereas others have shown a positive association. Horses (Equus caballus), especially those in equestrian sports, are prone to acute and chronic stress. My study aimed to ascertain whether and how play behaviours can ameliorate acute stress in horses from two different stabling and working conditions (i.e. housed in a stable or on a farm). My study involved investigating the behaviours and decision- making (cognition) of the individual horses in a Y maze for a food reward. All horses were exposed to three treatments in sequence, following a repeated measures design: baseline – without a stressor; stress - exposing the horses to a short-term acoustic stressor; and play - exposing horses to a short term acoustic stressor and then initiating object play with them. Treatments were repeated twice. I recorded the behaviours of the horses and later extracted the following variables: behavioural diversity (i.e. number of behaviours displayed/total potential behaviours); frequency of behaviours (number of behaviours per 10 seconds); emotional states (positive, negative and neutral), and the time taken (latency) for the horse to make a decision in the maze. I recorded whether they made decisions at two points: 1) the decision point in the maze and 2) for a food reward located at one terminal arm of the maze; the two decisions could be uncoupled. I collected saliva from each horse before and after each treatment for later analysis of cortisol levels. I found that the horses in the stress treatment showed greater diversity and frequency of behaviours linked to a negative emotional state as well as poor decision-making compared to the play and baseline treatments. Overall, decision-making was better in the play treatment than in the baseline and stress treatments. The horses at the stable, housed under more constrained conditions were more stressed than the horses on the farm. Male horses also appeared to be more stressed compared to the female horses. Salivary cortisol was not a significant predictor of any behaviours and decision-making, nor was it predicted by treatments, stabling or sex. I found that play is able to ameliorate stress behaviourally and that it improves decision-making, which indicates that play behaviour could be a useful indicator of animal welfare. It is, however, also evident that the behavioural and physiological response to a stressor appears to be decoupled in the horses selected for study.
Concurrent effects of elevated carbon dioxide and temperatures on the polyphenolics profile, in-vitro selected antioxidant and antimicrobial activities in Carpobrotus edulis (L.) leaves
(University of the Witwatersrand, Johannesburg, 2022) Sebothoma, Lethabo; Risenga, Ida; Nuapia, Yannick; Mayonde, Samalesu
Anthropogenic activities have led to the accumulation of carbon dioxide in the atmosphere and consequently the elevation of temperature. Carbon dioxide and temperature influence the physiological and biochemical activities in plants and thus, are important for plant survival, growth, and development. The sessile nature of plants prevents them from physically avoiding environmental factors such as high CO2 and temperatures, as a result they have developed a physiological response mechanism for protection. This mechanism involves the production of secondary metabolites, which in return have human-health benefits. How then is the production of secondary metabolites impacted by rising atmospheric CO2 concentrations and temperatures? Moreover, is the pharmaceutical efficacy of medicinal plants impacted as the atmospheric CO2 concentrations and temperature conditions rise due to climate change? This study therefore, aimed to investigate the possible modifications in the composition of polyphenolic compounds, antioxidant and antibacterial activities in Carpobrotus edulis leaves under controlled concurrent elevated atmospheric CO2 and temperatures. A total of 36 C. edulis potted plant samples, constituting 12 pots, divided into 3 pots per treatments were exposed to combined 600 ppm and 35/30°C (day/night), 600 ppm and 45/35°C (day/night), 800 ppm and 35/30°C (day/night), 800 ppm and 45/35 °C (day/night), respectively. The control samples were kept at ambient conditions of combined 400 ppm and 28/25°C (day/night). The plant samples were exposed to these conditions for up to 192 hours, and leave samples were harvested episodically every 48 hours (48, 96, 144 and 192 hours) during the exposure period. All harvested leave samples were air-dried under 40°C and crude extracts were obtained using methanol. Preliminary phytochemical screening was performed to test the presence of tannins, phenolics, flavonoids, steroids, terpenoids, 6 glycosides, and saponins. The LC-MS/MS method was used to profile the polyphenolic compounds and 2,2-diphenyl-1- picrylhydrazyl (DPPH) used to measure the antioxidant activity of the plant. The antibacterial activity of C. edulis was determined by the use of two popular bacterial strains, Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), using the Agar well diffusion method. The preliminary phytochemical screening results showed the consistent presence of tannins, phenolics, flavonoids, steroids, terpenoids, glycosides, and saponins throughout the treatments as compared with the control, however flavonoids were not detected in the samples under combined 800 ppm and 45/35°C, 600 ppm and 35/30°C as well as 800 ppm and 35/30°C. This indicated that combined elevated CO2 and temperatures could have impacted on the production of flavonoids. The LC-MS/MS results showed the presence of 24 polyphenolic compounds in Carpobrotus edulis leaves and of those only 14 (58.83%) were present in C. edulis leaves under ambient/control conditions. Furthermore, the concurrent increment of CO2 concentrations and temperatures prompted the appearance of 10 (41.67%) more compounds. A total of 17 (70.83%) polyphenolic compounds were identified under the 600 ppm and 45/35°C treatment. The presence of these 17 compounds seemed to be influenced by the duration of exposure to these conditions. Polyphenolic compounds profiling showed the disappearance of compounds and appearance of new compounds. The disappearance of some compounds was mainly observed under extreme conditions. Antioxidant activity decreased with increasing combined CO2 concentration and temperature exposure. Antimicrobial activity showed some inhibition of S. aureus and E. coli, and the inhibition activity remained constant in all the climatic conditions. This response maybe attributed to the appearance of new polyphenolic compounds. These results suggested that C. edulis is a strong antioxidant and antimicrobial agent, owing it to the polyphenolic compounds composition. However, these properties could be negatively impacted by elevated CO2 and temperatures, thus influencing the efficacy of C. edulis. Future studies could investigate the influences of elevated CO2 and temperatures independently to assess which factor plays the biggest role in the pharmaceutical efficacy of C. edulis
De novo production of Taxol intermediates by Saccharomyces Cerevisiae
(2022) Rabie, Renée
Taxol is an invaluable anticancer molecule produced by Yew trees and their endophytic fungi. Harvesting taxol is difficult and often has low yields. For these reasons, a method to produce taxol heterologously in a fast-growing, well-studied, safe microbe is desirable. In this study, artificial genes were designed for the expression of two taxol biosynthesis pathway enzymes, as well as an assisting NADPH-cytochrome P450 reductase. The genes were designed to be compatible with the pCut transformation technique, which allows genomic integration into Saccharomyces cerevisiae strain BY4742. The genes were then divided into seven fragments. Two additional DNA fragments were amplified directly from the yeast genome because their complexity made them difficult and expensive to synthesise. These nine DNA fragments were designed to be assembled into three linear fragments of equal length for transformation of S. cerevisiae. Attempts at assembling these nine fragments into three inserts failed for various reasons, which largely came down to the complexity and integrity of the DNA, as well as the size of the fragments.
A Partially Articulated Cynodont Encased in a Putative Burrow Structure from the Cynognathus Subzone C
(2015-10) Afonso, Nadia
A sedimentary structure containing a fossilized therapsid, and bioglyphs on the surface morphology, was found during a field expedition to Cynognathus subzone-C in the Eastern Cape, South Africa. A combination of surface scanning, petrographic thin sections, bone mapping and anatomical comparison were used to determine the deposit type and taxonomic identity of the encased therapsid, and examine the implications for biostratigraphy and faunal assemblage of the Cynognathus Assemblage Zone. The deposit is hypothesized to be a portion of a cynodont burrow (burrow margin) that was constructed in fluvial sediment near a river bank. This is the first account of a burrow in subzone-C. Pattern and directionality analysis of the bioglyphs suggest that the bioglyphs are scratch marks made by the burrower during excavation. The scratch marks are mediolaterally narrow, with some exhibiting indentation marks, indicating that the tracemaker had mediolaterally narrow unguals at the distal phalanx (claws). Anomodonts and cynodonts were common burrowers during the Triassic, however comparisons of Thrinaxodon and Lystrosaurus scratch marks to the bioglyphs on this deposit suggests that the bioglyphs were likely constructed by a cynodont as anomodont unguals are laterally wider, and are unable to create mediolaterally narrow markings. The tracemaker is hypothesized to be closely related to Thrinaxodon based on scratch mark comparison. However, bioglyph published literature is limited, and therefore the tracemaker cannot be identified. The therapsid was identified as Diademodon based on cranial and dental morphology. There is limited published literature on Diademodon constructing and/or exploiting burrows, however the taphonomy suggests that the Diademodon was near the entrance or in the tunnel of burrow nearing/during death. This is the first account of Diademodon encased in a burrow.
On the Triggering Mechanisms of Upward Lightning
(Nature Research, 2019-12) Schumann, C.; Saba, M; Warner, T.; Ferro, M.; Helsdon Jr, J.H.; Thomas, R.; Orville, R.E.
Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the continuing current that follows a positive return stroke.
Carnivore conservation needs evidence based livestock protection
(Public Library of Science, 2018-09) van Eeden, L.M.; Eklund, A.; Miller, J.R.B.; López-Bao, J.V; Chapron, G.; Cejtin, M.R.; McManus, J.
Carnivore predation on livestock often leads people to retaliate. Persecution by humans has contributed strongly to global endangerment of carnivores. Preventing livestock losses would help to achieve three goals common to many human societies: preserve nature, protect animal welfare, and safeguard human livelihoods. Between 2016 and 2018, four independent reviews evaluated >40 years of research on lethal and nonlethal interventions for reducing predation on livestock. From 114 studies, we find a striking conclusion: scarce quantitative comparisons of interventions and scarce comparisons against experimental controls preclude strong inference about the effectiveness of methods. For wise investment of public resources in protecting livestock and carnivores, evidence of effectiveness should be a prerequisite to policy making or large-scale funding of any method or, at a minimum, should be measured during implementation. An appropriate evidence base is needed, and we recommend a coalition of scientists and managers be formed to establish and encourage use of consistent standards in future experimental evaluations.
Chiefs in a Democracy: A Case Study of the 'New' Systems of Regulating Firewood Harvesting in Post-Apartheid South Africa
(MDPI, 2018-03) Findlay, S.J.; Twine, W.C.
Much of the international commons literature reveals a decreased functioning of local traditional institutions that regulate natural resource harvesting. In South Africa, it is believed that the creation of new democratic structures at the end of Apartheid has contributed significantly to the deterioration in traditional resource regulation and this in turn has led to the extensive resource degradation seen in parts of the country. Many of these assertions, though, remain anecdotal in nature. Given the high reliance by rural households on natural resources, and the serious negative implications that over-use has on livelihood security, understanding how well or poorly such commons are regulated is key to ensuring the sustainability of such resource-dependent populations. The aim of this study was therefore to examine systems of resource governance, focusing specifically on firewood, and to determine the roles of traditional and democratically elected community leaders in six rural villages spanning two chieftaincies in Bushbuckridge, South Africa. In each study village, five local leaders were interviewed and five community focus groups were conducted. Results indicate that most parties still regard the Chief as the ultimate authority for regulating firewood harvesting. However, overall firewood management appears weak, at best, across the region. Although some authors attribute this to community confusion over the roles of local leaders in a new democracy, we provide evidence that other socio-political factors, including political expediency, may be driving the increasingly relaxed implementation of these firewood management systems. With resource dependence remaining a vital contributor to livelihood security across the developing world and with many rural communities facing increasing strain under local resource depletion, these findings shed new light on the complex social dynamics underlying the widely reported weakening of traditional institutions in South Africa. In so doing, it offers insights into local firewood governance that can be used to combat these challenges and thereby reduce regional social and ecological vulnerability being experienced in communal landscapes across the region.
Transplant Experiments Point to Fire Regime as Limiting Savanna Tree Distribution
(Frontiers Media, 2018-09-18) Stevens, N.; Archibald, S.; Bond, W.J.
Plant species range shifts are predicted to occur in response to climate change. The predictions are often based on the assumption that climate is the primary factor limiting the distribution of species. However the distribution of grassy biomes in Africa cannot be predicted by climate alone, instead interactions between vegetation, climate and disturbance structure the ecosystems. To test if climatic variables, as predicted by an environmental niche model, determine the distribution limits of two common savanna tree species we established a transplant experiment at a range of latitudes and altitudes much broader than the distribution limits of our study species. We planted seedlings of two common savanna trees, Senegalia nigrescens and Colophospermum mopane, at eight paired high and low elevation sites across an 850 km latitudinal gradient in South African savannas. At each site seedlings were planted in both grassy and cleared plots. After 2 years of growth, rainfall, temperature and location inside or outside their distribution range did not explain species success. Grass competition was the only variable that significantly affected plant growth rates across all sites, but grass competition alone could not explain the distribution limit. Species distributions were best predicted when maximum tree growth rates were considered in relation to local fire return intervals. The probability of sapling escape from the fire trap was the most likely determinant of distribution limits of these two species. As trees grew and survived 100 s of kilometers south of their current range limits we conclude that climate alone does not explain the current distribution of these trees, and that climate change adaptation strategies for savanna environments based only on climatic envelope modeling will be inappropriate.
Biological and geophysical feedbacks with fire in the Earth system
(Environmental Research Letters, 2018-03-06) Archibald, S.; Lehmann, C.E.R.; Belcher, C.M.; Bond, W.J.; Bradstock, R.A.
Roughly 3% of the Earth's land surface burns annually, representing a critical exchange of energy and matter between the land and atmosphere via combustion. Fires range from slow smouldering peat fires, to low-intensity surface fires, to intense crown fires, depending on vegetation structure, fuel moisture, prevailing climate, and weather conditions. While the links between biogeochemistry, climate and fire are widely studied within Earth system science, these relationships are also mediated by fuels-namely plants and their litter-that are the product of evolutionary and ecological processes. Fire is a powerful selective force and, over their evolutionary history, plants have evolved traits that both tolerate and promote fire numerous times and across diverse clades. Here we outline a conceptual framework of how plant traits determine the flammability of ecosystems and interact with climate and weather to influence fire regimes. We explore how these evolutionary and ecological processes scale to impact biogeochemical and Earth system processes. Finally, we outline several research challenges that, when resolved, will improve our understanding of the role of plant evolution in mediating the fire feedbacks driving Earth system processes. Understanding current patterns of fire and vegetation, as well as patterns of fire over geological time, requires research that incorporates evolutionary biology, ecology, biogeography, and the biogeosciences.
Geology drives the spatial patterning and structure of termite mounds in an African savanna
(Ecosphere, 2018-03) Muvengwi, J.; Davies, A.B.; Parrini, F.; Witkowski, E.T.F.
Termite mounds perform important roles in savanna ecosystems, generating heterogeneity and influencing ecosystem processes across multiple trophic levels. However, the influence the environment and neighboring termite colonies have on mound spatial patterning and structure is poorly understood, despite the profound implications such dynamics can have on ecosystems. To better understand these drivers, we mapped the spatial distribution and size of active and inactive Macrotermes mounds in eight 1-km2 plots on contrasting geologies, nutrient-rich granite and nutrient-poor basalt, in a semi-arid Zimbabwean savanna. Although mound density was not significantly different between basalt (5.5 mounds/ha) and granite (6.1 mounds/ha), termite mound structural attributes and spatial distribution patterns varied greatly between geologies. Mound size distributions differed between the geologies and mounds were 2.6 times taller and 3.9 times wider and had 15 times greater lateral surface area on granite. Subsequently, 6% of the total landscape was covered by mounds on granite compared with only 0.4% on basalt. On granite, large mounds exhibited significant over-dispersion at scales below 30 m, signifying density-dependent thinning. Furthermore, small mounds were clustered around large mounds, likely a result of the budding of new colonies comprising fully fledged castes less vulnerable to competition. In contrast, random patterning was evident on comparably homogenous basalt. Our results demonstrate the powerful influence geological substrate has on mound spatial patterning and structure, suggesting that the importance of termite mounds for ecosystem functioning is more pronounced on nutrient-poor granitic substrates than basalts because of the pronounced over-dispersion, which maximizes mound production per unit area, and much larger mound sizes here.

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