Masters Degrees (Biological Sciences)

Permanent URI for this collectionhttps://hdl.handle.net/10413/12380

Browse

Now showing 1 - 20 of 71

Assemblages of surface-active arthropods in pristine and disturbed savannah.
(2022) Mavasa, Risuna Wain.; Tsvuura, Zivanai.; Yekwayo, Inam.; Mwabvu, Tarombera.
Savannahs are structurally complex ecosystems rich in biodiversity, and the conversion of savannahs into human-modified landscapes poses a significant risk to organisms with limited dispersal abilities. Surface-active arthropods have limited dispersal abilities and are sensitive to changes in their environment; as a result, they are restricted to specific habitats with the resources that they need. Surface-active arthropods are essential in ecosystem processes, such as playing a direct or indirect role in water infiltration into the soil and its storage, decomposition of plant and animal matter, nutrient cycling, humification and biological pest control. Many landscapes of natural vegetation in South Africa have been transformed into croplands, residential and commercial areas. In Mpumalanga province, croplands (including fruit plantations) dominate the landscape where savannah vegetation occurred previously. This study investigated the influences of disturbance (transformed savannah vs pristine savannah) and season on the diversity of four groups of surface-active arthropods (ants, beetles, millipedes and spiders) in the savannah biome in Mpumalanga province. The objectives of the study were to determine 1) whether flightless arthropod assemblages differ between disturbed and pristine savannah, and 2) whether functional guilds of flightless arthropod assemblages differ between summer and winter. Field sampling using pitfall traps was done to collect the surface-active arthropods in pristine and disturbed savannah during summer and winter. All samples were sorted into morphospecies and identified into family or genus where possible and then assigned into functional guilds. Functional guilds were allocated based on the feeding habits of the surface-active arthropods, resulting in three distinct functional guilds (detritivores, herbivores and carnivores) being identified. Surface-active arthropods with diverse feeding habits were lumped to form a fourth functional guild, the “diverse functional guild”. I found significant differences in the species composition of ants, beetles and spiders between disturbed and pristine savannahs. The species richness and abundance of ants was significantly greater in the disturbed than pristine savannah, while beetles and spiders had similar species richness and abundance between the two habitat types. The number of unique species of the surface-active arthropods in the disturbed savannah were two times more than those in the pristine savannah. The species richness and composition of all functional guilds of the surface-active arthropods differed between summer and winter, with greater species richness in summer than in winter. Herbivorous and carnivorous arthropods had significantly higher abundance in summer than in winter, while the abundance of detritivores and the “diverse functional guild” was similar between the two seasons. This study shows that different vegetation types support different compositions of surface-active arthropods and that there may be a positive relationship between vegetation structure and the assemblages of surface-active arthropods in the savannah. Furthermore, the study highlights a potentially positive relationship between the assemblages of herbivorous and carnivorous arthropods. I recommend that it may be essential to consider both disturbed and pristine habitat types in the conservation of surface-active arthropods, especially in South Africa where most of the land is outside of formal conservation areas. This assertion is supported by the greater number of unique species of surface-active arthropods found in the disturbed than in the pristine savannah. My study provides relevant baseline information because little is known about the assemblages of surface-active arthropods in savannah landscapes dominated by croplands. Furthermore, my study gives some insight on how the assemblages of surface-active arthropods may respond to disturbance in the savannah.
Assessment of roadkills in Hluhluwe-Imfolozi Park, KwaZulu-Natal, South Africa.
(2017) Mkhohlwa, Muzi Nicholas.; Downs, Colleen Thelma.
Anthropogenic land-use activities are considered to be the main contributor to current worldwide changes in natural ecosystems. South Africa is one of the countries that has been severely affected by changing land-use. The changes in land-use in South Africa are driven primarily by the need to provide food, water, and shelter to a growing human population and for economic growth. However, consequences of such actions impact biodiversity negatively with effects that lead to habitat fragmentation, loss of wildlife habitats, wildlife mortalities and species declines. One factor that contributes negatively is the increased number of roads and associated traffic. This study was conducted in Hluhluwe-Imfolozi Park (HIP), KwaZulu-Natal, South Africa, to assess roadkills on roads of the park. We conducted monthly roadkill surveys on three main roads (R618 corridor road traversing the HIP, paved road from Memorial Gate to Hilltop Resort, and an unpaved road from Memorial Gate to Isivivaneni Lookout) within HIP for a year. Furthermore, we assessed the public’s level of awareness about roadkills using questionnaire surveys. Relatively few roadkills were reported in our study when compared with other studies. The taxa that were reported as roadkills included mammals, birds, reptiles and amphibians. The R618 corridor road traversing the HIP had the highest number of roadkills, followed by the paved road then the unpaved road within park. Factors that contributed to reported roadkills were season, type of road, amount of game in the vicinity, and the distance to roadside vegetation from the road. In addition, the public showed limited awareness about roadkills occurring in HIP, but were aware of how they were expected to drive within protected area road networks. Mitigation measures such as mowing, signage, enforcement of harsh laws and introduction of fines were recommended as means that would help in the reduction of roadkills in HIP.
Behavioural responses of rodents to the scent and taste of compounds associated with sugar and protein degradation : implications for the evolution of chemical signals in rodent-pollinated flowers.
(2015) Records, Darryn.; Johnson, Steven Dene.; Nicolson, Susan W.
Volatile compounds in nectar may influence the behavioural responses of animal flower visitors, and thus have fitness consequences for both animal and plant mutualists. Rodents may use certain volatiles associated with sugar fermentation or protein degradation as a cue to locate food. Plants pollinated by rodents may thus emit these volatiles to enhance their attractiveness to rodents. However the presence of certain compounds in nectar may also indicate reward degradation, reducing its attractiveness to potential pollinators. The effects of these compounds on small mammal flower visitors are largely unknown and the consequences of nectar degradation by microorganisms for small mammal flower visitors need investigation. The present study examines the responses of a known rodent pollinator, the Namaqualand rock mouse Micaelamys namaquensis, an occasional floral visitor, the four-striped field mouse Rhabdomys pumilio, and a closely-related congener, the mesic four-striped field mouse Rhabdomys dilectus towards four compounds - ethanol, ethyl acetate, acetic acid and dimethyl disulphide - that are associated with the degradation of sugars and proteins. The study aimed to: (i) Identify if fermentation and protein degradation volatiles act as behavioural cues for small mammals, and have the potential to assist in the finding of food resources; and (ii) to determine the responses of rodents to the taste of volatiles in nectar. In chapter 1, I investigated whether fermentation and protein degradation volatiles elicit a behavioural response in small mammals, using a traditional Y-maze choice apparatus. Rodent species differed in their responses to the four volatiles tested. Ethanol emerged as an attractant for all of the species, with the strongest response seen at the 0.3 % ethanol concentration, while only R. dilectus responded positively to dimethyl disulphide. Acetic acid and ethyl acetate were generally not attractive. In chapter 2, the palatability of fermentation and protein degradation compounds at varying concentrations in experimental nectars was tested. A paired choice test analysis was used to determine if animals altered their choice with the addition of volatiles to sucrose solutions (0.73 and 1.46 M). Rodents showed a dose-dependent response towards the volatile concentrations presented to them. Both M. namaquensis and R. pumilio preferred medium (0.3 %) concentrations of ethanol in high sugar concentration diets, but found this compound distasteful in lower sugar concentration diets. Acetic acid and ethyl acetate were generally not preferred by any species at either sugar concentration. Dimethyl disulphide was preferred by all species when present in greater sugar concentrations (1.46 M) and at low volatile concentrations (0.003 %). These results suggest that rodents do alter their choice of nectar in relation to the tested compounds. I conclude that certain compounds associated with sugar fermentation or protein degradation have the potential to act as behavioural cues in rodent pollination and that further studies to reveal the effect of nectar degradation by microorganisms are needed to help in understanding plant-pollinator interactions.
Chemokines and haematological profile in Sprague-Dawley rats infected with trichinella Zimbabwensis and Plasmodium berghei ANKA.
(2017) Mdleleni, Yanga.; Mukaratirwa, Samson.; Murambiwa, Pretty.
Trichinellosis is an important re-emerging parasitic zoonosis caused by nematode species of the genus Trichinella and Plasmodium falciparum malaria is among the leading causes of mortality and morbidity in sub-Saharan Africa (SSA). Co-infection of the two diseases in rural communities is likely to be a common phenomenon although no reports have been made up to date. There is paucity of information on the consequence of co-infection regarding the clinical outcome of these diseases, especially malaria. Helminths, such as tissue-dwelling Trichinella spp larvae induce Th2 immune responses, while malaria induce Th1 immune responses as a survival strategy. On the other hand, chemokines are chemotactic cytokines produced by the host macrophages in order to elicit a protective immune response. Immuno-pathogenesis during co-infection remain obscure. It is against this background that this study aimed to determine host chemokine and haematological responses in male Sprague-Dawley rats during co-infection with Trichinella zimbabwensis and Plasmodium berghei. A 42 day follow up study was carried out, where 168 male Sprague-Dawley rats (90-150g) were randomly divided into four separate groups, control (n=42); malaria infected (n=42); Trichinella infected (n=42) and co-infected group (n=42). On day 0, male Sprague-Dawley rats were orally infected with 3 T. zimbabwensis muscle larvae per gram body weight. Followed at day 28 post-Trichinella infection with malaria induction using 105 P. berghei parasitized RBCs for the mono-infected group. While 42 male Sprague-Dawley rats were co-infected with T. zimbabwensis and P. berghei on day 0 and P. berghei infection occurred on day 28pi. Experimental animals were sacrificed on day 0,7,14,21,28,35 and 42 pi. Where whole blood and sera were collected. Plasmodium berghei percentage parastaemia, T. zimbabwensis adult worm count and muscle larvae load, haematological parameters and serum levels of IP-10, RANTES and EOTAXIN were determined. Co-infection with P. berghei and T. zimbabwensis showed elevated P. berghei percentage parastaemia, as well as upregulation of RANTES and EOTAXIN as a Th2 immune response, while IP-10 was downregulated as an effective immune response to parasitic infections. Mono-infection with P. berghei caused an upregulation of IP-10 as a Th1 immune response.
The curious case of the Satyrium neglectum complex: a taxonomic, ecological, and phylogenetic study.
(2021) Rule, Matthew James.; Van der Niet, Timotheus.; Johnson, Steven Dene.
Classical herbarium taxonomy uses a combination of morphological features from pressed specimens and distribution information as data in species delimitation. Whilst morphology is critical to species delimitation, additional information on phylogenetic relationships and fieldbased studies of ecology can inform taxonomic decisions. Satyrium neglectum Schltr. is a highly variable taxon currently comprising two subspecies, ssp. neglectum (Schltr.) A.V. Hall and ssp. woodii (Schltr.) A.V. Hall both of which are widely distributed in subtropical southern and eastern Africa. Variation in morphology and differences in apparent pollination systems, both between the subspecies, and within ssp. neglectum suggests the presence of two taxa within the current concept of the latter. This information, as well the exclusive reliance on herbariumbased taxonomy in the most recent species revision, formed the background to this re-evaluation of the systematics of the complex. A combination of detailed morphometrics and molecular phylogenetics demonstrated that the current concept of S. neglectum ssp. neglectum is inaccurate. A principal components analysis using traits measured from herbarium records from across the range, and ethanol-preserved flowers from South Africa, confirmed the presence of two morphologically distinct clusters within ssp. neglectum. Representatives from these two forms are separated along an elevation gradient. Bayesian inference using a combination of plastid and nuclear DNA sequence data revealed incongruent topologies. The nuclear topology is not consistent with current taxonomic boundaries, and revealed a separation between the high-elevation form and the low-elevation form of S. neglectum ssp. neglectum as well as ssp. woodii. The plastid data set also confirmed the separation of the high-altitude form of ssp. neglectum, but otherwise the topology reflects geography, as southern African accessions are separate from eastern African accessions. Floral scent was investigated in combination with published and novel pollinator observations in the Satyrium neglectum species complex. Floral scent composition and emission rates are mostly representative of associated pollination syndromes in previously published pollination work, with the exception of the high-elevation form. Published observations of ssp. woodii indicate that the species is pollinated by amethyst and the greater-double-coloured sunbirds, and the scent composition and emission rate is largely reflective of this. In addition, published observations showed a system of butterfly pollination in the low-elevation form of ssp. neglectum and long-proboscid fly pollination in the high-elevation form. However, new night time observations revealed additional pollination by settling moths in the high elevation form. These observations make sense in the context of the scent profile, which is dominated by compounds typically associated with moth pollination, such as phenylethyl alcohol and eugenol. In addition, two settling moths showed electroantennographic responses to the two dominant compounds in the scent bouquet of the high-elevation form. The compounds that dominate the scent of the butterfly-pollinated low elevation form are hexan-1-ol, octan-1-ol and benzyl alcohol, while previously published work on ssp. woodii showed that it is virtually unscented, and has emission rates that are markedly lower than other taxa pollinated by insects. Based on the morphological, phylogenetic and scent chemistry analyses, a case was made for the high-altitude form to be considered a separate taxonomic entity. This is formally described under the new name Satyrium basutorum. The analyses suggest that ssp. neglectum and ssp. woodii should be retained as subspecies, but a further investigation is required to identify the status of the eastern African synonyms Satyrium sceptrum and S. neglectum var. brevicalcar.
Cytokine and haemtological profiles in sprague-dawley rats experimentally infected with trichnella zimbabwensis and plasmodium berghei Anka.
(2017) Umo, Ekuyikeno Silas.; Mukaratirwa, Samson.; Murambiwa, Pretty.
Abstract available in PDF file.
Decadal changes in rocky shore communities in KwaZulu-Natal and survey methods for future monitoring.
(2020) Mvula, Philile Emelda.; Macdonald, Angus Hector Harold.; Pfaff, Maya Catherine.
Intertidal rocky shores form part of the sea during high tides and part of the land during low tides. They are therefore subjected to diverse anthropogenic pressures, including climate change, pollution, coastal erosion and harvesting. Due to their accessibility, rocky shores are among the most heavily exploited marine ecosystems. The rocky shores of the East and the South coasts of South Africa have been exploited for thousands of years. With growing coastal populations, they require management practices that ensure their ecological integrity and function. Rocky shore community structure along the KwaZulu-Natal (KZN) coast has been well studied between the years 1996 and 2000 when surveys were conducted at 39 sites. A monitoring Programme has since been established by Ezemvelo KwaZulu-Natal Wildlife in partnership with the Department of Environmental Affairs, Forestry and Fisheries (DEAFF) to inform the management of these heavily impacted ecosystems. This study aimed to contribute to the monitoring Programme in two ways: Firstly, by characterising and evaluating changes in rocky shore communities that have occurred since 2000, which was done by resurveying historical sites and comparing community structure and diversity between decades. Secondly, by comparing and evaluating different rocky shore sampling methods to identify the most suitable sampling protocol for a long-term monitoring programme of KZN rocky shores. This required statistical analyses of parallel surveys conducted using different methods. Significant changes in the community structure were observed with increased species richness and evenness. A decline in the abundance of harvested mussels was also noted, coupled with an increase in coralline algae and the arrival of two species of alien barnacles. Even though more long-term studies will be required to determine the status of the intertidal communities under anthropogenically induced change, the current study can be used to initiate better managementpractices in order to maintain species diversity and distribution.
Diet preference of common mynas (Sturnus tristis) in urban areas of Pietermaritzburg and Durban, KwaZulu-Natal.
(2017) Gumede, Silindile Thobeka.; Downs, Colleen Thelma.
Urbanization is one of the anthropogenic land use changes with a negative impact on biodiversity generally. However, some species are persisting well in urban areas and are termed urban exploiters. One of these species is the common myna (Sturnus tristis). It is also considered amongst the 100 worst alien invasive birds globally. As relatively little is known about the factors that affect common mynas invasive ability and urban persistence, aspects of their diet were investigated. Consequently, the main aims of this project were to investigate the macronutrient preference, sugar type and concentration preference, and assimilation efficiency of captive common mynas in the laboratory from July 2016 to March 2017. In addition, patterns of occurrence of common mynas in urban areas of Pietermaritzburg and Durban, KwaZulu-Natal, South Africa, and the influence of supplementary feeding and anthropogenic foods on their diet were investigated using questionnaires. Common mynas (n = 10) macronutrient preference was investigated in the laboratory where they were offered pairwise choices of three different diets (high in lipids diet, high in soluble carbohydrates (including sucrose) diet, and high in protein diet). Common mynas significantly preferred the high in lipids diet compared with either the high in protein diet or the high in carbohydrate diets. Common mynas (n = 7) were offered pairwise choices of three nectars (glucose, fructose and sucrose) to investigate their sugar type and concentration preference. Birds showed a significant preference for diluted glucose when given a choice of nectars. The sugar content of their excreta showed that they were unable to digest and absorb sucrose in nectar. Responses from the questionnaires showed that common mynas were found in the two study cities and were abundant year around. Results also showed that they were feeding mostly on anthropogenic foods compared with natural foods. Anthropogenic supplementary feeding has likely influenced the occurrence of common mynas because they follow food resources (human food waste) in urban areas and therefore successfully persist through lean periods. Further research is needed to help understand the ecology and behaviour of common mynas in order to get insights on how to monitor and control them in urban areas, in particular in South Africa where their range is expanding. Common mynas behaviour is currently poorly documented in South Africa. Since these are alien invasive birds with negative impacts in other countries, more research, especially on their behaviour, is required to prevent their negative impacts occurring in South Africa.
DNA barcoding of KwaZulu-Natal afromontane forest parmelia (parmeliaceae) species: a molecular approach to accurate specimen identification and sensitivity to climate change.
(2018) Ndhlovu, Nqobile Truelove.; Willows-Munro, Sandi.; Beckett, Richard Peter.
Accurate species identification is challenging, especially in groups with subtle taxonomically diagnostic characters such as lichens. Molecular-based techniques have shown to be a valuable tool for accurate specimen identification in fungi, in particular the use of DNA barcoding has become popular. Specifically, the internal transcriber spacer (ITS) region has been shown to successfully discriminate a broad range of fungal species. In this study, the utility of the ITS DNA barcode for use as a species diagnostic tool in the cosmopolitan lichen-forming fungus, Parmelia (Parmeliaceae) was investigated. Sixty-eight ITS sequences were generated from specimens collected from five sites around the province of KwaZulu-Natal and analysed. Phylogenetic analysis indicated that unlike European Parmelia species that form strong monophyletic clades, what appeared to be morphologically very similar Parmelia species in KwaZulu-Natal are paraphyletic or polyphyletic. No barcode gap was detected between the intra and interspecific distances. This suggests that the taxonomy of Parmelia lichens in South Africa needs to be thoroughly revised. The molecular data presented in this study provides evidence of previously hidden species-level diversity in Parmelia and as such contributes to the knowledge and understanding of the biodiversity of lichenized fungi in South Africa. The thermotolerance of Parmelia collected from different sites along an altitudinal gradient around Kwa-Zulu Natal was invesigated Chlorophyll fluorescence was used to assess the performance of lichen photobionts following stress, while ion leakage that of the mycobiont. For heat tolerance, results suggested that tolerance was correlated with the climatic conditions in which the lichens grow. Material from the coastal site of Hawaan were more heat tolerant than that from the three Midlands sites. Counter to our expectations, the coastal collections were more cold tolerant than those from the other sites. However, the genus clearly contains genetic variation with respect to stress tolerance, suggesting that it may have the potential to adapt to climate change.
Effects of high light intensity and desiccation stress on moss species.
(2021) Mbatha, Sikhethile.; Beckett, Richard Peter.
Bryophytes are desiccant tolerant non-vascular plants, capable of growing and surviving in extreme conditions. They are divided into three groups: liverworts, hornworts, and mosses. Most mosses grow in shady and moist environments, although some formpart of arid soil crusts where they protect soil from erosion. The moss flora of the Afromontane vegetation around Pietermaritzburg is dominated by two acrocarpous mosses, Atrichum androgynum, and Dicranella subsubulata. A. androgynum tends to grow in wetter, more shaded habitats and is a rather delicate species, while D. subsubulata grow in open, drier habitats and is more robust. Rarely, the species grow together, for example at the transition of a shaded indigenous woodland to plantations. We hypothesized that the more robust species has higher stress tolerance and has largely constitutive stress tolerance mechanisms. By contrast, we hypothesized that the more delicate species is less tolerant and may have inducible tolerance mechanisms. In the present study, desiccation tolerance and tolerance to high light stress were investigated in A. androgynum and D. subsubulata. Results confirmed that D. subsubulata was more tolerant of high light stress than A. androgynum. Exposure to moderate light intensities did not increase tolerance to subsequent high light stress in either species. Similarly, D. subsubulata was more desiccation tolerant than A. androgynum. Not consistent with our original hypothesis, mild desiccation, and treatment ABA-induced tolerance to desiccation in both species. Furthermore, detailed studies of the antioxidant enzyme peroxidase showed that enzyme activity was induced during slow drying in both D. subsubulata than A. androgynum. It appears that inducible tolerance mechanisms are present in both species. The work presented here represents a contribution to the autecology of two important mosses in the KwaZulu-Natal midlands Afromontane vegetation.
Efficacy of maslinic acid and chloroquine on the co-infection of Plasmodium berghei and Trichinella zimbabwensis in Sprague-Dawley rats.
(2015) Gcanga, Lorna.; Mukaratirwa, Samson.; Masola, Bubuya.
Many people living in Africa and elsewhere in the tropics suffer from combined malaria, soil-transmitted infections and tissue-dwelling nematodes. Most of these deaths are prevalent in sub-Saharan Africa (SSA) where the infections overlap, which often results in co-infection. Malaria and trichinellosis are one of the most important zoonotic diseases especially in sub-Saharan Africa caused by Plasmodium spp. and Trichinella spp., respectively. New drugs targeting malaria and trichinellosis have been examined with little success. The aim of our study was to determine and compare the efficacy of maslinic acid and chloroquine on the co-infection of muscle-dwelling larvae of Trichinella zimbabwensis and Plasmodium berghei in rats. Fifty-four Sprague-Dawley rats with an average weight of 150g and 200g for males and females respectively were infected with T. zimbabwensis and P. berghei. Infected rats were randomly assigned to nine groups which were subjected to treatments of maslinic acid and chloroquine and a combination of maslinic acid and chloroquine. Co-infected groups were infected with T. zimbabwensis on day 0, and then infected with P. berghei on day 30 post-infection (pi). Treatment was administered for 3 consecutive days on day 9 pi with P. berghei. Groups infected with P. berghei only were infected on day 0 and were treated on day 9 pi for 3 consecutive days. Groups infected with T. zimbabwensis only were infected on day 0 and treated on day 25 pi. Untreated control groups were a placebo (distilled water) on day 25 pi infected with T. zimbabwensis and from day 9 pi infected with P. berghei. In Trichinella-infected groups, the efficacy of each treatment measured by the rate of the reduction in muscle larvae was significant (P < 0.05) for both drugs compared to the untreated control group. In malaria-infected groups, the efficacy of each treatment, measured by the rate of reduction in parasitaemia, was significant (P < 0.05) for both drugs compared to the untreated control group. There was no apparent synergistic effect due to the combination of the two drugs in reducing the muscle larval burden and in reducing malaria parasitaemia. In all the treatment regimens, the reductions were significant when compared to the untreated control groups and not significant to each other (P > 0.05). From these results we can conclude that the efficacy of maslinic acid on the co-infection of T. zimbabwensis and P. berghei was comparable to that of chloroquine, making maslinic acid a promising drug to be used as an anthelmintic and anti-malaria against muscle larval stages of Trichinella spp. and malaria parasitaemia and no side effects were observed.
The emission of volatile organic compounds (VOCs) from rotting fruits and wilting flowers.
(2015) Ragubeer, Charlene.; Jürgens, Andreas.; Johnson, Steven Dene.
Plants and the microbes that feed on them produce a high diversity of volatile organic compounds (VOCs) that often mediate interspecies communication with other organisms. Two main functions of VOCs emitted by plants are to attract pollinating animals to flowers and seed dispersers to fruits; while volatiles emitted by microbes that feed on plant material can be used as cues by animals searching for food and can also facilitate dispersal of the microbes. The emission of VOCs from flowers and fruits often shows temporal changes that are characteristic for the different ripening stages of the plant organs. In many plants the VOC emission not only increases but also changes in its chemical composition during flower opening and fruit ripening respectively. In addition, VOC emission into the atmosphere carries information about the physiological status and stresses of the plant. However, the vast majority of studies that deal with the function of VOCs, e.g. for attracting pollinating animals or seed dispersers, focus only on those components that are emitted during the time when the plant shows the highest attractiveness for interaction partners. It is reasonable to believe, however, that the decisions made by animals, in terms of host preference and selection, are not only based on the chemical components that are emitted during times of optimal (nutritional) condition. The decision to utilize a flower/fruit is most likely also based on components that indicate to animals that a food source is not worth using, unpalatable, or toxic. For example, early stage flowers and unripe fruits have a low nutritional value, and late stage (wilted) flowers and rotten fruits may, in addition to already depleted resources, also contain toxic chemicals from microbial decomposition of the plant tissue. Compounds that are emitted from flowers and fruits are often difficult to detect with conventional headspace extraction techniques that use solvents. This is a particular problem for researchers interested in fermentation volatiles because many of the emitted compounds (e.g. ethyl acetate, acetic acid, acetoin) overlap in their retention time with solvents that are commonly used for extracting these compounds such as hexane, acetone, or dichloromethane. In this thesis two commonly used extraction techniques were compared: (i) solid phase micro-extraction (SPME) and (ii) micro solid phase extraction (Micro SPE), both the techniques are used to collect fermentation and floral VOCs. For Micro SPE two different chromatography columns (DB5 and Carbowax) were used to determine which is more sensitive in identifying compounds. For this, a floral and fermentation standard mixture was created by using compounds that represent sweet smelling flowers and rotting/fermenting fruits. Significant differences in the absolute emission of compounds, when using SPME and Micro SPE were found. There were also significant differences with the use of a DB5 and Carbowax column. The selection of the appropriate extraction technique for collection of VOCs should be based upon the type of application and availability of the necessary equipment. From this study, I found that Micro SPE worked better for collecting early to late stage VOCs of flowers and fruits, particularly if samples need to be collected under field conditions. To characterise the typical fermentation volatiles from flowers, the temporal variation in the emission of floral VOCs from the freshly opened to the wilted stages of three plant species namely: Hymenocallis littoralis, Dendrobium chrysotoxum and Camellia reticulata were investigated. The study revealed that there were significant differences in the absolute amounts and in some species also in the number of compounds emitted between early stage flowers and wilted flowers. Hymenocallis littoralis had a higher absolute emission of compounds on day one of flowering and thereafter emission decreased. However, no differences in the number of compounds were detected for this species. The VOCs of H. littoralis on the first day of sampling included: linalool, (1Z)-2-methylbutanal oxime, and 2-methyl-6-methylene-1,7-octadien-3-one, however the composition during the wilted stage included: (3E)-3-hexenyl acetate, heptenal, nonanal, and 2,6-dimethyl-7-octen-2-ol. There was a difference in the absolute emission of compounds for D. chrysotoxum, the emission increased until day six and thereafter decreased. There was also a difference in the number of compounds emitted, with more compounds being emitted from day 1 to 9 of sampling. The VOCs that contributed to the overall scent of the flowers of D. chrysotoxum from day 1 to 11 included: myrcene, linalool, limonene, 3,7-dimethyl-1,3,7-octatriene and α-pinene, however as the flowers began to wilt from day 12 to 13, the VOC composition changed and 4-dimethyl-1-heptene, limonene, terpinen-4-ol and (Z)-verbenol contributed to the late stage scent. For Camellia reticulata significant changes in the absolute emission and the number of compounds during the fresh and wilted flowering stages were detected. It was found that more compounds were emitted during the wilted stage. During the early stage of flowering, ethyl 2-(5-methyl-5-vinyltetrahydrofuran-2-yl) propan-2-yl carbonate, linalool, and 2H-pyran-3-ol, 6-ethenyltetrahydro-2,2,6-trimethyl- contributed to the scent of the flowers. During the wilted stage, benzaldehyde, benzyl alcohol, (E)-2-Hexen-1-ol, and 2-Heptanol contributed to the scent of the flowers. To investigate typical fermentation volatiles three plant species, Musa acuminata (banana), Pyrus communis (pear) and Rothmannia globosa, were selected. For the three selected species, the temporal variation in the emission of VOCs from fruits during the ripening process (i.e. ripe to overripe stages) were investigated. Significant differences in the absolute amount and number of compounds emitted were detected. For M. acuminata, there was a higher absolute emission and number of compounds emitted from sampling day 1 to 10. Acetoin and 2,3-butanediol contributed to the scent of rotting M. acuminata. For P. communis, more absolute emission took place on day 1 of sampling and thereafter decreased, followed by an increase at day 35 of sampling and thereafter decreasing. Hexyl acetate, n-butyl butanoate, 1-hexanol and n-amyl acetate were found during the ripe stage of the fruit, and the VOC composition changed during rotting with the occurrence of ethyl acetate, acetic acid, 3 methyl-1-butanol, phenylethyl alcohol and benzaldehyde. Rothmannia globosa was sampled during the ripe and overripe stages. Higher absolute emission and number of compounds were emitted during the ripe stage of the fruit. 1-hexanol contributed to the scent of R. globosa during the ripe stages, however during the rotting stage, n-butyl acrylate, benzaldehyde, 1-butanol and 2-ethyl-1-hexyl acetate were found in samples. The findings of this study have relevance for researchers that are interested in the role of temporal VOC changes for the behaviour of pollinators and seed dispersers. Furthermore, it may be beneficial to researchers interested in the chemicals that are emitted by flowers that mimic rotting fruit volatiles. It is likely that microbial VOCs together with VOC changes initiated by the plant play an ecological role for host selection in animals. However, there is still a gap in our knowledge regarding the functional role of these VOCs and further studies are needed to investigate how such changes affect animal behavior and host selection. In addition, some of the findings of this study might be of interest for more applied areas such as horticulture and agriculture where the detection of microbial VOC signatures is important for detecting microbial pathogens, early senescence, and decomposition of plant tissue.
Epigenetic priming and in vitro mutagenesis in sugarcane (Saccharum Spp. Hybrids) for resistance to fusarium species and Eldana saccharina (Lepidoptera: Pyralidae).
(2022) Govender, Eshani.; Watt, Maria Paula.; Snyman, Sandra Jane.; Rutherford, Richard Stuart.
In the South African sugar industry, there have been substantial economic losses of R1 billion/annum caused by the indigenous pyralid borer, Eldana saccharina (Lepidoptera: Pyralidae). To develop control measures for E. saccharina in sugarcane, it is important to understand the interactions between the stalk borer and Fusarium spp. In previous studies, in vitro assays have shown that Fusarium strains may be antagonistic (e.g., F. sacchari PNG40) or beneficial (e.g., F. pseudonyamai SC17). F. pseudonyamai SC17 is a potential endophytic indicator of E. saccharina infestation, as the association between borer infestation and infection by the fungus causes Fusarium stalk rot in sugarcane. Studies have reported that the presence of endophytic fungi may have several benefits to the host plant, e.g., the production of phytohormones such as indole-3-acetic acid (IAA), which promotes plant development. The study aimed to: 1) choose a suitable resistance priming agent between hexanoic acid (Hx) and cis-jasmone (CJ); 2) determine an appropriate culture filtrate (CF) concentration for in vitro screening of calli and plantlets for tolerance to F. pseudonygamai; 3) develop a protocol (epigenetic priming and mutagenesis) to generate mutants: primed only (0.6 mM Hx), a combination of priming and mutagenic agents (100 μM 5-AzaC + 16 mM EMS-induced); 4) screen for indole-3-acetic acid production by F. pseudonygamai; and 5) characterise in vitro selected mutants for E. saccharina and F. pseudonygamai resistance by comparing the levels of resistance between unprimed, primed, and primed + mutagenic plantlets through ex vitro screening. When cis-jasmone (CJ) and hexanoic acid (Hx) were investigated for their effect on priming for pathogen resistance, 0.6 mM Hx was selected as the optimum priming agent concentration for both the callus and plantlet regeneration stages. At the highest CF concentration (100 ppm) at the embryo germination stage, the number of plantlets was greatly reduced to 58 and 98 plantlets/0.1 g of callus, for cultivars 88H0019 and N41 respectively, compared to more than 600 plantlets/0.1 g of callus in the no CF control. Unexpectedly, in the plantlet regeneration stage all the tested CF concentrations had a significant positive effect on the percentage of plantlets that re-rooted compared with the control. Both cultivars showed a 95 - 100 % rooting ability of the plantlets, which was significantly higher than the percentage of plantlets that rooted in the embryo germination media (EGM1) containing no CF (60 - 70 %) (p < 0.001). Likewise, all the concentrations of the CF had a positive effect on the root length of plantlets, with 1500 ppm CF resulting in the highest root length of 31.5 mm ± 4.3 for 88H0019 and 34.05 mm ± 3.9 for N41. Hence, F. pseudonygamai SC17 could not be used as an in vitro selection agent in a root re-growth assay. Due to the enhanced effect of F. pseudonygamai SC17 CF on root growth, the fungal isolate’s potential to produce indole acetic-3-acid (IAA) was assessed. F. pseudonygamai produced the highest IAA concentration (743.1 nM) in the presence of L-tryptophan than in the treatment without L-tryptophan (457.2 nM). This suggests that the observed enhanced root growth may be due in part to the production of auxin (IAA) in the F. pseudonygamai SC17 CF. Acclimatised in vitro plantlets (8-9 months old) were inoculated only with F. pseudonygamai SC17 or dual inoculated: firstly, with F. pseudonygamai SC17, then 1-2 2nd instar E. saccharina larvae that were placed into the leaf whorls 2 weeks later. To confirm tolerance of the putative mutants, fungal isolations were performed on the stem sections above the inoculation lesion from symptomatic and asymptomatic plants. The results revealed that the putative mutant plants that were primed with Hx only and treated with a combination of mutagens (EMS and 5-AzaC) and priming agent exhibited a significant decrease in lesion severity as compared with controls. For both treatments, a mild lesion severity rating was recorded for plants inoculated with only SC17 for cultivars N41 and 88H0019. For the plants that were dual inoculated there was a significant difference in the lesion severity ratings between the two treatments (p < 0.001). The lesion severity rating was moderate for cultivar 88H0019 (primed with Hx) and mild for cultivar N41 (primed with Hx). Plants from the combined treatment for both cultivars resulted in a mild lesion severity rating. This protocol could be valuable in generating commercially important cultivars that are tolerant and resistant to F. pseudonygamai SC17 and possibly other sugarcane pathogens. Planting resistant cultivars is recommended as an economical and the best method for controlling diseases and pests. This approach used in this study will have the least impact on the environment and increase yields without the need for expensive chemical applications and labour.
An estimation of oxidative metabolism in relation to desiccation tolerance, chilling sensitivity and hydrated storage lifespan of recalcitrant seeds from tropical and temperate provenances .
(2017) Ramlall, Chandika.; Pammenter, Norman William.; Berjak, Patricia.
Abstract available in PDF file.
Feeding dynamics of invasive (Tarebia granifera) and native (Melanoides tuberculata) freshwater gastropods.
(2020) Naidoo, Senine.; Carrasco, Nicola Kim.; Miranda, Nelson Augusto Fernandes.
Tarebia granifera has invaded several South African estuaries, outnumbering native gastropods such as Melanoides tuberculata. Comparative feeding dynamics can aid in estimating and understanding invasion impacts. This study aimed to explore the feeding dynamics of these gastropods with the use of two different approaches. Stable Isotope Analyses (SIAs) were used to investigate the dietary preferences and niche overlaps in the St Lucia Estuary, while Functional Response Experiments measured the relationship between the consumption rate of a food resource and its availability. These experiments were run both with and without the presence of heterospecific chemical cues (secondary metabolites secreted by either species) to determine whether chemical cues influence the functional responses of T. granifera and M. tuberculata. Mixed species experiments were also conducted to observe individual behaviour (active, inactive and feeding) over time and measure resource consumption when both species are placed together under high and low food availability. The SIA showed that both gastropods exhibited generalist diets, however, due to niche partitioning, there was no significant difference in their dietary niche overlap. In the FR experiments, both species exhibited Type II FRs and had similar feeding rates. However, in the presence of heterospecific chemical cues, M. tuberculata exhibited a higher feeding rate at high food availabilities, whereas T. granifera showed efficient feeding dynamics under limited food resources. In the mixed species experiments, T. granifera spent more time feeding under low food availability while M. tuberculata spent more time feeding under high food availability. This study showed that in certain conditions (e.g. high resource availability) the alien species did not always have a feeding advantage. A multiple method approach is recommended when assessing ecological impacts of invasive species.
Field evaluation and characterisation of the mode of imazapyr tolerance in three mutant sugarcane genotypes.
(2016) Singh, Varnika.; Watt, Maria Paula Mousaco Deoliveira.; Snyman, Sandra Jane.; Rutherford, Richard Stuart.
Abstract available in PDF file.
The financial and economic feasibility of biodigester use and biogas production for rural households.
(2011) Smith, Michael Trevor.; Blignaut, James N.; Goebel, Jessica Schroenn.
In South Africa, sustainable development is set in the context of two separate economies. The second of these economies consists of the rural population and is characterised by poverty and stagnant development. Sustainable development is an increasingly topical concept which highlights the need for development to proceed in a manner that does not deplete natural resources. In addition to narrowing the gaps between the various classes (layers) in an economy, the key ‘ingredients’ of sustainable economic development include “natural resource management, food, water, and energy access, provision and security” (Blignaut, 2009: cited in Blignaut and van der Elst, 2009: 14). A biodigester is a potential solution to some of the difficulties faced by remote rural populations. Biodigester systems are submerged tanks capable of producing a nutrient rich fertiliser and combustible gas when consistently fed with organic matter and water. A biodigester may be one simple answer to the key ingredient needs of sustainable development – reducing the depletion of natural resources, providing clean burning energy for cooking and fertiliser for growing food. The potential is clear for biodigesters to aid in the process of sustainable development. The question to be analysed is whether this technology would be financially and economically feasible for installation and use in rural households. This thesis focuses on a typically remote and rural community in KwaZulu-Natal, South Africa, in order to assess the potential feasibility of a biodigester system. The appraisal takes the form of a Cost Benefit Analysis (CBA) and aims to establish whether or not this technology is financially feasible for individual rural households and/or economically beneficial to society.
Foliar secretory cavities of Vepris lanceolata (Lam.) G. Don (Rutaceae): micromorphology and chemical composition of the secretion.
(2017) Nxumalo, Nozipho Ntombikayise.; Naidoo, Yougasphree.; Naidoo, Gonasageran.
Secretory structures such as ducts, trichomes and cavities consist of cells that are primary sites synthesizing essential oils and other phytochemical compounds with medicinal properties. Little is known about the micromorphology of secretory structures and the composition of the chemical constituents. There was no information documented on the micromorphology of secretory structures of Vepris lanceolata (Lam.) G. Don (Rutaceae family). The aim of this research was to investigate the micromorphological characteristics of foliar secretory cavities, the chemical composition of the secretion, and the antibacterial activity of leaf extracts of Vepris lanceolata. Scanning electron microscope (SEM) images by chemical fixation and freeze drying revealed no external secretory structures on the surfaces of leaves. SEM images by freeze-fracture showed secretory cavities present in the leaf blade. The cavities were embedded amongst palisade and spongy parenchyma cells, next to the vascular bundle. Cavities were made up of the lumen surrounded by varying layers of epithelial cells, depending on the secretory phase of the cavity. Semi-thin and ultra-thin sections showed that foliar cavities develop schizo-lysigenously, i.e. cavities develop by both separation and degradation of epithelial cells. Transmission electron microscope (TEM) sections showed that during the secretory stage, secretory cells contained oil droplets, vacuoles and vesicles indicating active secretion. Histochemical assays of fresh leaves showed the localization of phytochemical compounds. Cavities turned orange red when stained with Sudan III indicating the presence of lipids and pink with NADI reagent to show essential oils. Cavities also stained positive for polysaccharides, sugars, phenolic compounds, proteins and alkaloids. Phytochemical screening showed the presence of alkaloids, glycosides, carbohydrates, proteins, tannins, phenolic compounds, flavonoids, fixed oils and fats. Preliminary thin layer chromatography (TLC) showed separation of bands indicating groups of active compounds in leaf extracts. Crude (ethanolic and methanolic) and water extracts of leaves showed antibacterial activity against gram positive bacteria Staphylococcus aureus (ATCC 25923) and methicillin-resistant Staphylococcus aureus (ATCC BAA-1683); and five strains of gram-negative bacteria: Escherichia coli (ATCC 25922), Escherichia coli (carbapenem-resistant) (ATCC BAA 2340), Klebsiella pneumonia (ATCC 314588), Pseudomonas aeruginosa (ATCC 27853), as well as Salmonella typhimurium (ATCC14026) according to the disc diffusion method. Leaf extracts have tannins, alkaloids, flavonoids, essential oil and flavonoids responsible for the antimicrobial activity of the plant.
Friendly neighbours? Investigating ecological facilitation between Thunbergia atriplicifolia (Acanthaceae) and Exochaenium grande (Gentianaceae).
(2018) Msweli, Simangele Mbali.; Johnson, Steven Dene.; Shuttleworth, Adam.
Wildflowers that co-exist, share similar floral signals and flower simultaneously, may interact with the same pool of pollinators, therefore sharing pollinator species and individuals. Floral similarity could be a result of a common ancestor, convergent floral syndrome or mimicry. Pollinator sharing may have consequences for the pollination success and fecundity of one or more of the interacting wildflowers. This study was conducted in grassland vegetation of southern KwaZulu-Natal to investigate an observed floral similarity between Thunbergia atriplicifolia and Exochaenium grande, document pollinator sharing between the two species and investigate the consequences of pollinator sharing on (1) interspecific pollen transfer between the two species and (2) seed set of individuals of E. grande that grow within sparse and dense populations of T. atriplicifolia. It was hypothesized that E. grande is a mimic of T. atriplicifolia. Investigated aspects of floral similarity include: flowering phenology, flower colour, flower size and nectar production. Weekly surveys indicated that both species flower simultaneously but E. grande occurs at much lower density and peaks in flowering later than does T. atrplicifolia. Flowers of the two species have similar spectral reflectance and in terms of a bee vision model can be considered indistinguishable to bees. There is also overlap in flower size of the two species. They provide similar amounts of nectar but nectar of E. grande has a higher sugar concentration. Both species are dependent on pollinators for seed production and are pollinated by generalist solitary bees belonging to the Apideae and Hactilidae family, with some species shared by both plant species. Stigmas of T. atriplicifolia and E. grande carried heterospecific pollen in varying degrees. Estimates of pollen production indicated that E. grande produces more pollen than T. atriplicifolia. Although interspecific pollen transfer was confirmed, it is not yet clear whether this improper pollen transfer affects seedset. Plant density of E. grande and T. atriplicifolia was not a significant predictor of seed set in E. grande. However, there were very high levels of seed predation in E. grande, and that hinders our ability to rule out the any effects of pollinator sharing in seed set. These findings reveal a striking similarity and pollinator sharing between the two species, but despite this, there appears to be no negative or positive effects of this on seed set. Seed set only accounts for half of fitness, however, and the effects of pollinator sharing may therefore be evident on other measures of fitness. The role of trait similarity for pollinator attraction still requires further experimental investigation before the hypothesis of ecological facilitation (or mimicry) can be accepted.
The functional role of birds as pollinators in southern Cape fynbos.
(2018) Whitehead, Kellyn Jean.; Johnson, Steven Dene.; Brown, Mark.
Nectarivorous birds, particularly sunbirds, are important pollinators of plants in the Cape Flora of South Africa, being responsible for pollinating approximately 5% of plant species. However, interactions between plants and nectarivorous birds in the eastern part of the Cape Floristic Region have not received much attention. This study focussed on two putatively bird-pollinated plant species found within the Nature’s Valley area, namely Kniphofia uvaria and Chasmanthe aethiopica. The breeding systems were determined for each species and, due to their patchy population distribution, potential Allee effects on plant fecundity were also tested for. Flowering phenology in the area was also examined to test for associations between flowering of bird-pollinated plant species and the temporal presence of nectarivorous birds. Selective exclusion experiments showed that sunbirds were the main pollinators of K. uvaria and C. aethiopica – fruit set and the number of viable seeds were much higher for untreated (open control) individuals where birds could visit flowers freely, compared to caged individuals which only allowed for insect visitation. Very few seeds developed when plants of the two species were bagged to exclude all pollinators, indicating that the species are not capable of autonomous self-fertilization. Fruit and seed set were determined for patches of K. uvaria and C. aethiopica in order to test for potential Allee effects. There was a significant relation between the percentage of flowers that set fruit and the number of plants per patch for both K. uvaria and C. aethiopica. However, the number of seeds set per flower of K. uvaria and C. aethiopica had no significant relation with the number of plants per patch. Flowering phenology for the area was determined by bi-weekly walks along the two study sites to document plants in flower. Bird presence was determined using data collected from bi-weekly mist netting sessions at the two sites. We then compared the presence of birds with the flowering data of bird-pollinated plant species. For the Kalander Kloof site there were ten bird-pollinated plant species found and eight for the Salt River site. A comparison of the flowering data with bird presence data, indicated that nectar feeding birds were more likely to be present when accessible nectar availability is high. A total of 135 plant species across both sites were documented during the period of this study of which 14 were bird pollinated.

Browse

Browsing Masters Degrees (Biological Sciences) by Title