Biological Sciences

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Aardvark and people: can a shy species be widely known in a localised area?
(2022) Makwati, Nolutho.; Kraai, Manqhai.; Tsvuura, Zivanai.
The increase in human populations has led to humans sharing space with wild animals even in the natural habitats of the animals. Conflicts may arise when people and wildlife attempt to fulfill their needs which can be detrimental to one or both parties, and this type of conflict is called human-wildlife conflict (HWC). The human needs include people hunting wild animals for consumption of the animal and trading in animal body parts.Hunting is one of the factors that decreases populations of numerous animal species, and it occurs in many parts of the world e.g. in Africa, Asia and South America, where it contributes to extinction of species. The conservation and management of burrowing animals is a major challenge due to their elusive and nocturnal behaviour. The aardvark is an African medium-sized, burrowing mammal whose conservation status has not been updated recently due to the difficulties associated with studying nocturnal animals. Aardvarks may play a significant ecological role in the ecosystems in which they occur, such as by changing the landscape through their digging activities, or through affecting the dispersal of seeds. Therefore, the aim of this study was to explore the influence of humans on population trends and activity patterns of aardvarks outside protected areas, and to determine people’s perceptions about the animal. The study was conducted in Ncunjane village in Msinga Local Municipality, KwaZulu-Natal Province of South Africa. To understand people’s perceptions about aardvark in their community, I used a semistructured questionnaire survey. I asked personal information of the participants (sex, level of education and age), and questions related to people’s perceptions about the aardvark, such as people’s knowledge, myths, and their uses of the animal or its body parts. To determine activity patterns of the animal, I focused on aardvark foraging activities in a semi- arid savanna ecosystem that is also used as a communal rangeland over eight months between 2020 and 2021. I measured and quantified aardvark foraging holes using 53 50 m × 10 m transects where there was evidence of aardvark activity. In addition, I quantified aardvark burrowing of dens in the dry, wet and early dry seasons using walking transects guided by a research assistant who knows the area. I found that people have different perspectives about aardvark with the majority (78%) of respondents having strongly positive perceptions. The positive perceptions arise from aardvark not causing physical harm to people, and fleeing away upon sighting people. I found that aardvarks were mainly hunted for meat while some animal body parts were sold to traditional healers for traditional medicine. All seasons consisted of a greater number (> 51%) of old than new and very old foraging holes.The surface area of new, old, very old holes differed significantly with season (P < 0.0001) and the depth of new, old and very old holes also varied with season (P < 0.0001). In addition, the contents of foraging holes varied with age of the hole and season in that new holes lacked evidence of plant life across seasons. Aardvark dens were used by other animals such as spiders, wild cats, Cape porcupines and snakes. Hence, an increase in aardvark holes can be associated with significant landscape heterogeneity for vegetation and animal life. Aardvarks in Ncunjane fed close to their dens presumablyto mitigate against human predation through hunting threats, which may directly affect the extent of aardvark digging activities. These results show that aardvarks may be categorised as ecosystem engineers as the burrows provide shelter for other animals, also, their effects on other animals are disproportionate to their abundance. These results highlight that aardvarks are threatened by human uses and may decline in abundance in the area. Finally, aardvarks remain poorly studied in landscapes shared with humans. Further studies to assess aardvark numbers in human-dominated landscapes are required which can raise awareness and play a significant role in conservation of aardvarks.
Above- and belowground competition in Savanna systems.
(2008) Payne, Michelle Jennifer.; Kirkman, Kevin Peter.
The structure and composition of savanna vegetation is influenced by resource availability and disturbance. Grasses, a major component of savannas, influence this resource availability by competing directly with trees for light, water and soil nutrient resources. The direct causes of bush encroachment are not always apparent, but are commonly ascribed to overgrazing and consequent decreased grass competition. The interaction, both above and belowground, between tree and grass seedlings and the surrounding grass sward is dependant on many factors, such as soil depth, seedling species and sward composition. These factors, as well as the presence or absence of defoliation, in the form of grazing or fire dictate whether the system will remain in a transition state as savanna or move towards a stable woodland state. The major competitive effects experienced by the tree seedlings were dependant on grass species and nutrient level. A. nilotica was affected by aboveground competition while A. karroo was affected by belowground competition. E. capensis caused the greatest decrease in A. karroo plant biomass. Both E. capensis and H. hirta had large competitive effects on the aboveground biomass of A. nilotica, while S. africanus had the greatest effect on belowground biomass. Increasing nutrient availability resulted in an increase in the competitive effect exerted on A. karroo, while little to no change was seen in the competitive effect exerted on A. nilotica. Soil depth constrained plant size in both tree species. The intensity of belowground interactions on tree biomass was unaffected by soil depth, while aboveground competition had a significant effect on shallow soils. Belowground competition was also of greater importance than aboveground competition in dictating tree seedling height. Grass seedlings growing on all three soil depths differed in mean mass, with E. racemosa having the least mass and T. triandra having the greatest. Simulated grazing by cutting the surrounding sward resulted in biomass increases in all three grass species. Changes in savanna composition and structure are thus likely to be influenced by initial species composition and soil depth and soil nutrient composition. While grazing creates niches for grass seedling establishment, heavy grazing has been observed to increase grass seedling mortality. Encroachment is thus more likely to occur on intensively grazed shallow and deep soils than on medium depth soils. This highlights the importance of ensuring the grass sward remains vigorous by resting and monitoring stocking rates to ensure veld is not over-utilized. It is then possible to maintain some form of tree-grass coexistence at a level where available grazing is not compromised.
Above-ground allometry, biomass and nutrient content of acacia mearnsii across four ages and three sites in the Kwazulu-Natal Midlands.
(2005) Dovey, Steven B.; Pammenter, Norman William.
Acacia mearnsii (black wattle) is one of the few tree crops of which both timber and bark are utilised, with branches sometimes being collected for fuel wood. There is a great potential for nutrient loss from plantations with intense harvesting practices. Allometric relationships were developed to estimate above-ground biomass across four ages and three site qualities of A. meamsii stands. The three sites were based on high, medium and low site quality classes of productivity. Differences in biomass and the distribution of biomass between the stem, bark, live branches, dead branches and foliage components are described in relation to site and age. Relationships between biomass and light interception and plant area index are investigated and show some merit. Nutrient concentrations were used with the above-ground biomass data to estimate quantities of nutrients held in the various biomass components in each of the stands. Nutrient distributions in the above-ground biomass (AGB) were examined and compared to other studies. Foliar phosphorus (P) and potassium (K) concentrations were shown to be sub optimal, agreeing with results and recommendations of South African fertilisation stupies. Some concentration differences were observed between site and age classes for certain nutrients, although these differences may have been due to seasonal effects. Biomass and nutrient quantities were adjusted to yield a wood production of 100 t ha01 and compared with adjusted calculations for similar studies on other plantation crops. Total nutrients contained in the AGB of the adjusted calculations were 540.8 kg ha01 nitrogen (N), 20.4 kg ha-I P, 200.6 kg ha01 K, 241 kg ha-I calcium (Ca), 55.7 kg ha-I magnesium (Mg), with a half to two thirds of the nutrients held in the stem and bark alone. Nutrients losses vary with harvesting intensity as bark and branches may be harvested with the stem wood. Levels of nutrient removal with harvesting intensity are discussed with reference to estimated losses and gains from natural processes and management practices. An incomplete nutrient budget calculation indicated that P, K, Ca and Mg might potentially be removed in quantities greater than replaced by natural processes under stem and bark harvesting. The budget calculations lack processes such as leaching and N-fixation. It is highly probable that these processes, once quantified, may yield more negative budget results, especially for the base cations K, Ca and Mg.
Abscisic acid and other hormonal effects on growth in Spirodela.
(1969) Van Staden, Johannes.; Bornman, Chris H.
The effects of abscisic acid In particular, as well well as gibberellic acid and the cytoklnlns, 6-benzyladenine, kinetin, and 6-dlmethylal lalylamlnopurine, on the growth of Spirodela oligorrhiza were investigated. Abscisic acid effectively arrested growth permanently at concentrations down to 10¯¹ mg/I. Normal growth tended to be resumed at concentrations of 10¯² and 10¯³ mg/l between nine and twelve days after treatment. A concentration of 10[-8] mg/l, however, resulted in a significant increase in dry weight at both eight, nine and twelve days after introduction into the culture medium. It is suggested that the resumption of growth twelve days after treatment at those concentrations which inhibit growth up to nine days, was due to a possible progressive inactivation of abscisic acid resulting in a lowering of its concentration to a level that is promotive. It was furthermore found that the growth response of Spirodela in terms of dry weight production over a period of eight days is proportional to the log[10] concentration of abscisic acid. It is suggested that this curve can be used as a relatively reliable and easily performed bioassay to detect amounts of abscisic acid as low as 10[-5] μg. The assay is more reliable over the range 0.01 to 10,000 μg and appears not to be affected by gibberellin, benzyladenine and kinetin. The inhibitory effect of abscisic acid on growth in Spirodela was shown to be reversed by benzyladenine, kinetin and dimethylallalylaminopurine, although they were not equally effective in doing so. Benzyladenine at 1.0 mg/l was the most effective In overcoming growth inhibition by abscisic acid. Gibberellic acid, however, proved ineffective in reversing the inhibitory effect of abscisic acid on Spirodela oligorrhiza. The apparent Increases in growth obtained in some cases may have resulted more directly from gibberellic acid stimulation than from the Interaction of gibberel lie acid with abscisic acid.
Achene biology and the chemical control of Chromolaena odorata.
(1985) Erasmus, Daniël Jacobus.; Van Staden, Johannes.
Abstract viewable in PDF document.
The actions of, and interactions between, auxins and cytokinins and their effect on in vitro rooting of selected Eucalyptus clones.
(2011) Nakhooda, Muhammad.; Watt, Maria Paula Mousaco Deoliveira.; Mycock, David John.
Clonal propagation of Eucalyptus spp. and its hybrids allows for competitiveness in the commercial forestry industry through the propagation and preservation of superior/elite genotypes. Vegetative propagation through rooted cuttings is the industry‟s standard and the choice of clones selected for plantations are determined by their rooting ability. However, as many potentially valuable genotypes are recalcitrant to adventitious rooting, micropropagation is the only effective means of propagating them. Micropropagation results in high plantlet yields, achieved primarily through the empirical use of the key plant growth regulators (PGRs) cytokinins and auxins, for shoot and root production, respectively. Their selection for use in vitro is driven by their effects on percent rooting rather than root quality. Little is known regarding the quality of the roots of the plantlets ex vitro, but there is some evidence that they are different from those of seedlings and cuttings. It was therefore hypothesized that the properties of exogenous PGRs and their interaction with other exogenous and endogenous PGRs, influenced root development and subsequent root quality. This was tested in vitro using a good-rooting E. grandis (TAG31) and two poor-rooting E. grandis x nitens hybrid clones (GN155 and NH58). In the former, the auxins supplied during the pre-rooting culture stages (multiplication and elongation) were sufficient for 100% rooting in an auxin-free rooting medium. Different combinations of PGRs in the two pre-rooting stages, followed by rooting without auxins, revealed a direct relationship between the stability of the supplied auxin and the rooting ability of TAG31. Gas chromatographymass spectrometry (GC-MS) analyses indicated that endogenous shoot levels of indole- 3-acetic acid (IAA) influenced graviperception. Also, low IAA content was associated with atypical starch grain accumulation or its absence from root tips (53.1 nmol IAA gˉ¹ DW compared with 325.7 nmol IAA g-¹ DW in gravisensing roots). The specific roles of the natural auxins IAA and IBA on root morphogenesis were then investigated using 2,3,5-triiodobenzoic acid (TIBA; inhibits IAA transport), ρ-chlorophenoxyisobutyric acid (PCIB; inhibits auxin signal transduction), and the auxin antagonist kinetin in the rooting medium, following root induction. After 3 weeks, the mean root diameter was significantly reduced from 552.8μm (control) to 129.2μm (with PCIB) and 278.6μm (with kinetin). TIBA increased root diameter to 833.4μm, decreased Δ root length, increased root vasculature and resulted in agravitropism. Hence, whereas rooting could be induced by IBA, IAA was necessary for the maintenance of vascular integrity and graviperception. This critical role of IAA in root development is of importance as IBA, owing to its higher stability, has been traditionally relied upon for root induction in the majority of micropropagation protocols. The potential of incorporating IAA into the media formulations of in vitro protocols for poor-rooters that do not respond well to IAA was then investigated, using GN155 and NH58. While PCIB in the rooting medium of GN155 completely inhibited rooting, the addition of dihydroxyacetophenone (DHAP), an inhibitor of auxin conjugation, to the rooting medium, did not significantly increase % rooting in the presence of 0.1 mg 1ˉ¹ IBA (i.e. 50% rooting with 2mM DHAP and IBA, compared with 45% with IBA alone). The results suggested that the inability of some eucalypts to induce roots easily in vitro was not due to a deficiency in auxin signal transduction or to auxin conjugation. Instead, rooting was inhibited by an accumulation of kinetin within shoots during the pre-rooting culture stages. The endogenous levels of PGRs in shoots of GN155 and NH58 showed a strong relationship (R² = 0.943) between the shoot kinetin:auxin and shoot rootability. Substituting kinetin with the relatively less stable natural cytokinin trans-zeatin in the elongation stage resulted in a significant increase in % rooting in both clones, from 19% to 45% (GN155) and from 31% to 52% (NH58), with 0.1 mg 1ˉ¹ IAA in the rooting medium. However, omitting all cytokinins from the elongation medium, resulted in over 95% and 75% rooting of shoots of GN155 and NH58, respectively, with 0.1 mg 1ˉ¹ IAA. These results suggest that IAA is a requirement for root development and cannot be substituted by its analogues in certain root developmental events. Hence, IAA should be the preferred auxin for eucalypt micropropagation. As fundamental research, the approach taken in this study circumvents the empirical method used in improving micropropagation protocols. The importance of the properties and the interactions between endogenous and exogenous PGRs in regulating root morphogenesis, and the practical implications of these findings is emphasised.
Adventitious rooting in stem cuttings of Eucalyptus grandis Hill ex Maid.
(1988) Wilson, Philip John.; Van Staden, Johannes.
Adventitious rooting in stem cuttings of Eucalyptus grandis Hill ex Maid. was thought to be influenced by a putative inhibitor. In previous studies it has been usual to infer the presence of putative rooting inhibitors and promoters from the mung bean bioassay, but the possibility was raised that treatment responses in this assay could be mediated more by the concentration of the treatment solution than by the chemical identity of the solute. This appeared to be so: several solutes, including hydrochloric acid and common salt, were found to promote the rooting of mung bean cuttings when present in the treatment solution at an apparently injurous concentration. The concept of promoters and inhibitors of adventitious rooting, as constituted at present, was considered to be an unfavourable approach for further studies. Stem cuttings must contain a morphogen, broadly defined, which operates the 'switch' from stem to adventitious root. The leaves and buds of E.grandis stem cuttings did not appear to be sole sources of a morphogen (as is often assumed), but nevertheless the activity of the leaves and buds was good for rooting. This activity was reflected in the pattern of root emergence. A slight preponderance emerged from the leaf trace sectors of the stem, suggesting that the leaves and buds cause a morphogen (of unknown origin) to circulate in the cutting. The existence of a vascular morphogen was confirmed and it proved to be very mobile in the stem, suggesting that it is well distributed circumferentially at the base of the cutting rather than confined to the leaf trace sectors. It appeared to be super-abundant at the base of easy-to-root cuttings, but it was not possible to tell to what extent the morphogen was rendered accessible to the sites where roots initiate. In general, the rate of efflux from the transporting tissues, the rate of attenuation of the morphogen after efflux, and the number of potential sites for root initiation must interact on a small scale to determine rooting ability. The relative prominence of these groups of factors would be expected to vary with circumstances, for example at different locations within a single stem cutting, so the traditional concept of a limiting morphogen ('rhizocaline') is unhelpful in its simplest form. Nevertheless, the rhizocaline concept provides a starting point towards a more comprehensive view of adventitious rooting, which is required in order to predict and improve rooting ability. This view remains a remote objective because many of the factors which could be important have recieved very little attention and will be difficult to elucidate.
Aligning elephant conservation with societal aspirations.
(2022) Van de Water, Antoinette.; Slotow, Robert Hugh.
Protection of biodiversity and social development often seem at odds in the world of today. The aim of this thesis is to show that it does not need to be that way. Most global social compacts focus on either economic development, or biodiversity conservation. Few prioritise the needs, values and rights of local people living in or near conservationsensitive areas. If biodiversity and human well-being goals are to be realised simultaneously, we must find ways to increase land use for conservation purposes, while respecting the values and needs of local people and future generations. In an effort to contribute to this aim, this thesis explores and analyses how elephants are valued and perceived by a wide range of stakeholders; it investigates why narrow conservation approaches fail; and it uses the research outcomes to develop an alternative roadmap for conservation, one that realises beneficial outcomes for elephants, people and the environment. Through literature review, participatory workshops, questionnaires, interviews and reports provided by reserves and provincial government, I developed: (1) the TUSKER framework to reconcile integrity of nature with human well-being, (2) the pluralist elephant valuation system to incorporate all values of elephants that I have been able to uncover and provide insight into trade-offs associated with conservation decisions, (3) a theory of change for human-elephant coexistence and building common ground, and (4) a One Well-being framework to holistically assess and rank the consequences of elephant management interventions at different scales of animal, human and environmental well-being. The frameworks can be used in strategies that promote animal well-being and range expansion, while simultaneously empowering local communities and enhancing local economies. They may be employed by policymakers and managers to work towards ‘living-in-harmony’ conservation schemes, in which elephants and other iconic species do not represent a threat to humans but a chance for development and joy. Through ‘Living in harmony’, ‘convivial conservation’, and the incorporation of African philosophy Ubuntu (a philosophy that recognises moral values such as justice, dignity and rights), we will move towards a more ethical, just, and sustainable world.
Alkaloids of Catha Spp.
(2001) Field, Courtney Robin.; Smith, Michael Trevor.
The levels of the psychoactive alkaloids S-(-)-cathinone and its primary metabolite cathine, consisting of the diastereomers (+) -norpseudoephedrine and (-)- norephedrine were determined in Catha edulis (Vahl) Forssk. ex Endl., Catha transvaalensis Codd and Catha abbottii Van Wyk & Prins. Alkaloid levels were investigated in C. edulis plants collected from three different localities in South Africa, and one from a Nairobi khat market. The efficiency of three different methods for the extraction and isolation of cathinone and cathine were investigated, viz. an aqueous acid extraction, an organic solvent extraction and an aqueous acid extraction using the commercially available Extrelutᴿ procedure. The aqueous acid extraction resulted in the rapid loss of cathinone and yielded variable alkaloid levels in replicate studies. This was also observed when this method was coupled with the Extrelutᴿ procedure. In contrast, the organic solvent extraction did not result in a loss of cathinone and provided consistent results over a number of replicates; it also proved to be a simple and rapid method for extracting and isolating cathinone and cathine. A trifluoroacetic acid (TFA) derivatization procedure which has been suggested to produce characteristic diagnostic fragments for gas chromatography / mass spectrometry (GC/MS) identification, was investigated, but failed to produce consistent TFA derivatives of cathinone and cathine. However, underivatized cathinone and cathine were easily identified by GCMS due to their unambiguous mass spectra. All subsequent studies were undertaken using the organic solvent extraction and isolation method, coupled with GC analysis and GC/MS identification of underivatized cathinone and cathine. Leaves of C. edulis were found to contain cathinone and cathine at levels 100 times higher than those of C. transvaalensis. The alkaloids were undetectable in C. abbottii. Plants grown from cuttings of C. edulis collected from the Durban Botanical Gardens were found to contain cathinone and cathine at levels of 0.410 mg per gram fresh weight and 0.157 mg per gram fresh weight in leaves, respectively, while these levels in plants derived from different localities decreased in the order: Eastern Cape (0.319 mg/g f.w cathinone and 0.029 mg/g f.w cathine), Mpumalanga (0.139 mg/g f.w. cathinone and 0.171 mg/g f.w. cathine) and Nairobi (0.032 mg/g f.w. cathinone and 0.025 mg/g f. w. cathine). In an investigation of the cathinone levels in the different plant parts it was found that the highest levels were found in leaves of the shoot tip (0.243 mg/g f.w.) but decreased with the age of the leaf and developmental stage of the plant in the order: juvenile leaves (0.124 mg/g f.w.), mature leaves (0.035 mg/g f.w.), young stem (0.033 mg/g f.w.) and mature stem (0.004 mg/g f.w.). Concomitantly, cathine levels increased with the age of the leaf: leaves of the shoot tip (0.006 mg/g f.w.), juvenile leaves (0.011 mg/g f.w.), mature leaves (0.019 mg/g f.w.). The cathine level in the young stem material was found to be the highest in the entire plant (0.270 mg/g f.w.) but decreased markedly in the mature stem (0.052 mg/g f.w.). Both cathinone and cathine levels in the mature root were greater than levels in the mature stern, being 0.012 mg cathinone per gram fresh weight, and 0.063 mg cathine per gram fresh weight. Neither cathinone nor cathine were detectable in young root material.
Alleviating delayed field curing-induced deterioration in rice seeds by cathodic water invigoration: a comparison of seed and seedling responses in two upland rice species and their interspecific hybrid.
(2021) Bam, Raphael Kwame.; Varghese, Boby.; Naidoo, Sershen.; Pammenter, Norman William.
Rice constitutes the major source of the world’s food supply. A number of varieties are grown in many parts of the world, all which produce orthodox seeds that are usually stored between growing seasons. As in other crop species, storage-induced loss of seed quality (viability and vigour) is inevitable but considerable research effort has been invested in optimising seed bank storage protocols for rice to ensure acceptably high levels of seed germinability and seedling emergence. However, poor post-harvest practices such as delayed field curing before threshing in developing countries in the humid tropics, such as Ghana, result in curing-induced seed deterioration in the field prior to ex situ storage. Given that many rice growing regions are likely to experience significant levels of climate change, seed processing and storage induced declines in rice seed quality could exacerbate the crop losses incurred by rice farmers in these regions in the future. This motivated the present study which was designed around three aims: 1) to investigate how environmental conditions and the duration of field curing influenced seed macro-structural integrity, susceptibility to microbial infection, and seed germinability and vigour; 2) to identify macro-structural and ultrastructural indicators/ biomarkers of field curing and associated storage-induced stress/ damage; 3) to assess whether the invigoration of field-cured seeds with cathodic water (CW), an established antioxidant-based seed invigoration medium, and deionized water (DW) can alleviate the deteriorative effects of delayed field curing on rice seed cellular integrity, germination and subsequent seedling growth and biomass. The specific objectives of this comparative study, which involved an Asian (Oryza sativa L.) and African (Oryza glaberrima Steud) upland rice species and their interspecific hybrid (O. sativa × O. glaberrima), were as follows: a) to compare the impacts of delayed field curing in wet and dry environments on seed physical, physiological and pathological quality; b) to identify potential ultrastructural biomarkers of seed sensitivity to delayed field curing-induced stress/ damage in embryonic root meristematic cells using transmission electron microscopy (TEM); c) to assess whether CW invigoration alleviates cellular stress/ damage induced by delayed field curing using selected ultrastructural biomarkers of seed sensitivity to such curing-induced stress/ damage; and d) to assess whether invigoration with CW and DW improves seed germinability and emergence, and subsequent plant growth in field cured seeds, relative to non-invigorated (NI) dry seeds.
Aluminium-induced gene expression in sugarcane roots.
(2002) Graham, Natalie Jane.; Watt, Derek Alexander.
Due to the increasing prevalence and severity of Al phytoxicity in certain regions of the South African sugar industry, a research programme has been initiated at SASEX to elucidate the molecular mechanisms by which sugarcane detects and responds to the metal. As part of this larger investigation, the current study aimed to assess the response of a reportedly Al tolerant cultivar, Saccharum spp. hybrid cv. N12, to phytotoxic levels of Al. Hydroponically-grown plants of this commercial genotype were used in Al inhibition studies, the results of which indicated that exposure of plants to 250µM Al for 24 hours resulted in maximum reduction of root elongation. Under these conditions, root growth was inhibited by approximately 36%, compared with only 4% for the 50µM Al treatment. Subsequently, this exposure regime was used to gather the terminal 5 to 10mm of root tips, the site of the primary Al lesion, of challenged and control, unchallenged plants for molecular analysis. Total RNA was extracted from the Al challenged and control root tips, from which mRNA was subsequently isolated, reverse transcribed and converted to double-stranded cDNA. The two populations of cDNA were reciprocally subtracted from each other and used to construct subtractive cDNA libraries in Lambda ZAP®II phages. Randomly selected clones, 576 representatives from each of the libraries, were screened using membrane-based array technology. Results indicated that only 33% (190) of the Al-treatment specific library cDNAs were found to be more highly expressed under conditions of Al stress than under control conditions. Of these potentially Al response-related cDNAs, 25 were sequenced and submitted to sequence databases for the assignment of putative identities. No genic sequences known to be directly associated with the Al stress response were identified, however, several were found to be related to pathogenesis or general stress pathways. Although further Northern hybridisation work is required to validate these results, they suggest that the induction of general stress response pathways may be involved in the aluminium stress response of this sugarcane cultivar. Such Al stress-related sequences could have applications in marker-assisted breeding programmes and as candidate genes for the genetic engineering of tolerant genotypes.
The analysis of erythropoiesis and other early developmental events in the chick embryo using mesodermal-inducing factors.
(1994) Gordon-Thomson, Clare.; Fabian, B.
The causal and temporal aspects of blood tissue specification in the chick embryo were investigated in this study. The main focus was on the role of basic fibroblast growth factor (bFGF) in the determination of the erythropoietic tissue, particularly in context with its representation as a non-axial mesodermal derivative which arises in the posterior domain of the chick embryo. The initial strategy employed in this study was the use of agents that are known to block the activity of bFGF, and to determine their effects on erythropoiesis. Treatment of unincubated chick embryo explants with heparin, which binds specifically to the FGF family, was found to inhibit primitive streak formation and erythropoiesis, and also inhibited the formation of other mesodermal tissues. These initial findings suggested that one or more growth factors had become bound to the heparin, and that their activity is important for the specification of primitive streak formation and mesodermal patteming. The development of the erythropoietic tissue was assayed by a cytochemical test for haemoglobin using 0dianisidine; and by histological examination for blood islands and red blood cells in serial sections of the embryos after 48 hours incubation. Microscopic examination of the embryos at the stages of gastrulation on the first day of incubation revealed that heparin caused holes to appear in the ventral layer; and although a primitive streak did not form, a middle layer of mesenchymal cells were seen to accumulate between the ectodermal and ventral "endodermal" layers. It was significant that heparin's inhibitory effect on erythropoiesis could be reversed after the addition of a recombinant bovine bFGF to the heparin-treated embryos. However, the exogenous bFGF did not neutralize the inhibitory effect of heparin on the primitive streak and other mesodermal derivatives (Chapter Two). The inhibition of erythropoiesis by heparin was also reversed by the addition of a mesodermal-inducing factor extracted from a Xenopus embryonic cell line, namely XTC. The XTC mesodermal-inducing factor (MIF), which belongs to the transforming growth factor-B family and is a homologue of activin, could also reverse the inhibitory effect of heparin on primitive streak formation; but no recognizable axial mesodermal structures subsequently developed. Of consequence, was that both bFGF and XTC-MIF blocked heparin's effect on the ventral layer, preventing the gaps forming. Therefore, it is suggestive that the VI development of an intact ventral layer is important for the determination of the erythropoietic sequence (Chapter Three). By taking a more specific approach using antisera to bFGF (anti-FGF) and the bFGF receptor (anti-FGFR) on whole embryo explants, it was found that anti-FGP and anti-FGFR were able to inhibit erythropoiesis, but not primitive streak formation. However, these antisera caused defects in the posterior region of the embryonic axis. These embryos not only lacked posterior blood tissue, but heart and somites were missing; whereas the anterior head structures were well formed. These results therefore suggest that bFGF signalling is important for the development of the posterior body plan, which includes erythropoiesis (Chapter Four). Further evidence for the role of bFGF in the determination of the blood mesodermal tissue line was reached in an in vitro bioassay. In this part of the investigation, specific pieces of the blastoderm, namely pieces dissected from the posterior marginal zone (PMZ) and inner core of the central disc (lCD) were able to form haemoglobin under particular conditions. The PMZ components were found to have the capacity to form haemoglobin when dissected from blastoderms of stages X to xm when cultured in serum-free medium. This commitment to form haemoglobin could be blocked by treatment with anti-FGP at stages X and XI, but not at the later stages of xn and XIII. The ICD components were found to have a commitment to form haemoglobin only if this component was dissected from embryos at stage XIT and XITI, but not before. These results suggest that a determinative event for the haemoglobin differentiative pathway occurs between stages XI and XII. It was also found that the stage X central disc component could be induced to form haemoglobin if a stage xm hypoblast was added to it in tissue recombination sandwich cultures, or if bFGF (75 - 150 ng/ml) was added to the medium. These results lend further support that bFGF plays an important role in the determination of erythropoiesis; and furthermore, suggest that the hypoblastic tissue is the source of this induction (Chapter Four). Finally, immunocytochemical labelling with a polyclonal antibody to bFGF has revealed that bFGF increases significantly from stage XI in cells within the developing hypoblast layer and in the middle mesodermal layer. These cells are located predominantly in the posterior domain of the embryo. This polarized distribution of bFGF with the high value of bFGF concentration in the posterior area, is presumably responsible for inducing the overlying epiblast to form the posterior horseshoe-shaped region from which blood tissue is seen to arise. An immunocytochemical analysis of the distribution of the FGF receptor was vu assessed, as an indicator of the possible competence of the cells to respond to the bFGF signal. The bFGF receptor was found to be expressed at stage XII in cells that appeared to be in register with those immunoreactive to the bFGF ligand; therefore suggesting an autocrine function. It was interesting that at stage Xli an intense immunostaining with the anti-FGFR developed in the nuclei of cells within the epiblast layer (Chapter Five). In conclusion, this study has demonstrated that the initial determination of the erythropoietic cell lineage in the chick is at the time when the hypoblast is in the process of forming beneath the epiblast, Le. between stages XI and XII. Furthermore, it was found that an induction by an FGF-like signal from the hypoblast layer (or middle mesodermal cells that may be closely associated with the hypoblast) induces "competent" cells (Le. FGFR-positive cells) in the epiblast to form blood tissue in the posterior domain of the chick embryo.
Analysis of historical flowering data, investigations into aspects of pollen biology and selected biotechniques to complement sugarcane breeding in South Africa.
(2016) Mhlongo, Nonsikelelo Yvonne.; Snyman, Sandra Jane.
Abstract available in PDF file.
The Anostraca (crustacea : Branchiopoda) of southern Africa.
(1994) Hamer, Michelle Luane.; Appleton, Christopher Charles.
The Anostraca are a group of crustaceans belonging to the class Branchiopoda. They are predominantly restricted to temporary, inland waterbodies, which in southern Africa, include rockpools, animal wallows, and large "pans". The anostracan fauna of southern Africa was last examined in detail in 1929 by Barnard, and recent collecting in a number of areas indicated the need to update earlier work. A total of four genera, each belonging to a separate family, and forty-six species, some of which had not previously been described, are presented in this thesis. The monogeneric family Streptocephalidae is well represented in Africa, and the fauna of Africa south and north of the Zambezi and Kunene Rivers, as well as Madagascar is reviewed. The Streptocephalus species are characterised by having an S-shaped antennal process, terminating in a cheliform "hand" region. The species were divided into ten groups based on similarities in antennal process morphology. The descriptions of five new species have been published, and an update on distribution and specimen data for a number of species are presented. An additional, as yet unpublished new species from Zimbabwe is presented. The genus Artemia, although well researched in other parts of the world, has been largely ignored in southern Africa. Bisexual populations occur along the Cape coast, and a set of specimens from Namibia, which includes only females, may indicate that A. parthenogenetica is also present on the subcontinent. The frontal knob morphology of the Cape specimens is similar to that of A. tunisiana from northern Africa and the Mediterranean. The family Branchipodidae is characterised by the fusion of the basal joints of the male antennae to form a so-called "clypeus". This family is represented in southern Africa by a diverse fauna of the genus Branchipodopsis. Eleven previously described species, as well as five new species are presented. An attempt was made to divide the sixteen species into species groups, as was done for the streptocephalids, but this proved difficult. The taxonomically useful characters in this genus are largely restricted to the basal processes. An additional character, the presence of expansions of the posterior thoracic segments in the females of some species could be useful. Much intraspecific variation in clypeus morphology was evident, particularly in two of the widespread species. Branchipodopsis species commonly occur in small pools which fill a number of times during the wet season and this has probably led to the development of localised adaptations, and intraspecific variation, or even species endemic to very restricted areas. Three sets of specimens which belong to the family Branchipodidae, but to no known genus, were recently collected from north-eastern Natal, the eastern Cape and the Namib desert in Namibia. These specimens share a single, large process positioned medianly on the fused basal joints, as opposed to a pair of processes in this position. However, the morphology of the penes, and the position and form of other antennal processes could indicate that the specimens are not congeneric. Unfortunately, more material is necessary before the descriptions of two of these possible new genera can be published. Three species of the genus Branchinella, of the family Thamnocephalidae, occur in southern Africa. These species have a well developed frontal process, and fully retractible penes. Bran chin ella spinosa was recorded from the Makgadikgadi Pan in northern Botswana, and was probably introduced to this area from north Africa, or Europe, where it has a wide distribution. The other two southern African species have been collected from few localities, and in small numbers, and this may be connected to cyst hatching processes. The southern African anostracan fauna exhibits distinct distribution patterns and these . appear to be influenced by climate, with rainfall having the dominant influence in the western half of the subcontinent, and temperature influencing distribution in the eastern half. The high altitude Escarpment forms a barrier to the movement of species between the coastal margin and the central plateau region. The formation of the Escarpment could have resulted in vicariance speciation in some anostracans, but in most cases, allopatric speciation appears to have occurred. The type of habitat also influences species distribution in a number of ways. The great anostracan species richness in southern Africa is probably related to the climatic heterogeneity of the subcontinent, as well as the possible origin of two genera in Gondwanaland, and the absence of a Pleistocene glaciation in Africa. Large parts of southern Africa have not been sampled, and the exact status and distribution of many species is uncertain.
Another culture of Solanum genotypes.
(1995) Liebenberg, Denise.; Van Staden, Johannes.
Being the third most cultivated crop in South Africa, potatoes are of great economic importance. As potatoes originated from cooler areas in the world, they do not easily adapt to South African conditions. The main objective of potato breeding is, therefore, to extend the crop's limited genetic base. Progress in crop improvement is slow due to dominance, segregation and other factors caused by the tetraploid character of cultivated potatoes. A new breeding program for rapid progress has been initiated at the Vegetable and Ornamental Plant Institute, Roodeplaat, South Africa, which comprises the combination of conventional and unconventional breeding techniques. The program is based on the reduction of the ploidy level from the tetraploid to the dihaploid level to facilitate crossings with diploid wild species. Anther culture is the preferred technique for the rapid reduction of the ploidy level and has been successfully applied on different members of the Solanaceae. Cultivated potato, Solanum tuberosum is, however, an important exception. In this study various potato genotypes (tetraploid cultivars, dihaploid breeding lines and a diploid wild species) were used in experiments concerning microtechniques, alternative culture methods and medium manipulation. The main objectives were to evaluate and compare the androgenetic ability of the various genotypes used and to try and identify the factors limiting their in vitro response. Regarding microtechnique, the study focussed on the investigation of the frequency of androgenesis - as a function of plant age - and the determination of defined flower bud lenqths representative of the correct microspore developmental stage for optimal androgenetic response. Combined with an extensive histological study on the microspore development within anthers, from the time of flower selection, after a cold-pretreatment and at various time-intervals during the culture period of 42 days, the following conclusions were reached: In vitro androgenetic response proved optimal when flowers of responsive genotypes were selected during the first seven to 21 days of the flowering period. Both microspore derived embryoid- and callus development were visible within responsive anthers after a culture period of only seven days. The flower bud length required for anthers to be in the optimal stage of microspore development, e.g. the uninucleate stage, varied between the different genotypes but could readily be determined with the DAPI (4,6-diamidino-2- phenylindole) technique. It was also concluded that anthers of the tetraploid cultivar Atzimba should be selected later, between the late-uninucleate and the early-binucleate developmental stages. This suggested a limited selection period for Atzimba anthers, as starch depositioning - which prevent embryogenesis - occurs within anthers during the binucleate stage. Histologically, Atzimba showed limited embryoid development with no embryoid release, while the diploid wild species, S. canasense, proved androgenetically unresponsive. Alternative culture methods were applied to study the effect of different culture phases (liquid, double layered and agar solidified) and anther orientations (lateral, dorsal and ventral) on the androgenetic response of the potato genotypes used. Liquid cultures, based on the so-called shed-pollen technique, enhanced the androgenetic response of the tetraploid cultivar Atzimba. Optimal embryogenesis was obtained for responsive breeding line 87.2002/3 with the utilization of agar solidified media, with maximal response when anthers were cultured in the lateral orientation. No response was observed from S. canasense. The effect of medium manipulation on the androgenetic response of the three genotypes was investigated. The utilization of various combinations of different concentrations of indole-3-acetic acid (1M) and benzyladenine (BA), the alteration of the initial time of incubation of anthers on the initiation media and the use of media without growth regulators compared to that containing gibberellic acid (GA[3]), were investigated. BA had to be present in the initiation media and had a major, though not exclusive, effect on embryogenesis compared to 1M. The optimal BA concentration varied between the two trials. IAA also had an increasing effect on anther response, both in the absence of BA and, especially, in addition with relatively high BA concentrations. In this experiment, only breeding line 87.2002/3 responded. The initial culture of anthers, during the first seven to 21 days of the culture period, on media containing growth regulators proved essential for microspore derived embryoid production in the tetraploid cultivar Atzimba. As these growth regulators are metabolized in the culture media, the regular transfer at shorter, two-weekly intervals to media containing metabolically active substances, proved important. GA[3] had no enhancing-effect on embryogenesis in any of the three tetraploid cultivars. The results obtained in this study suggest that the first 21 days is the critical stage in the anther culture period in terms of the optimal time for flower selection, embryoid induction and the increase in embryogenetic response due to growth regulator influence. It is important to pre-determine the developmental stage when most microspores were in the uninucleate stage of development and to correlate this stage with a specific flower bud length. This would assure maximum response of those genotypes amenable to anther culture. It also implies a more practical and economical starting pOint to anther culture experiments. Following the determination of microspore developmental stage and pollen fertility, flowers should be selected from the donor plants only during the first three weeks of the flowering period. The composition of the nutrient media used for potato anther cultures were sufficient with respect to growth regulators. The growth regulators SA, IAA and the amines glutamine and asparagine had to be present in the initiation media, especially during the first three weeks of the culture period. As microspore development within anyone anther was found to be asynchronous, the regular transfer of anthers to fresh media is recommended to assure proper development of all microspores. The use of a slightly higher IAA concentration could be considered, but care should be taken as too-high concentrations would induce callus production. Microspore derived embryoid production is preferred, as the ploidy level of callus derived plantlets normally varies and somaclonal variation can occur. Liquid media should be considered for anther culture of tetraploid genotypes, while embryoid production can be increased by culturing the anthers of responsive genotypes on agar solidified media on the lateral orientation. Finally, the diploid wild species S. canasense seemed androgenetically unresponsive, or the media and culture conditions used did not satisfy the specific requirements of this genotype. Androgenetic amenability should first be transferred by means of interspecific crossings with a responsive dihaploid genotype, such as the breeding line 87.2002/3.
Ant communities along an elevational transect, the Udzungwa Mountains in Tanzania.
(2020) Kunene, Caroline.; Munyai, Thinandavha Caswell.; Foord, Stefan Hendrik.
Understanding biodiversity patterns and the processes that structure them along environmental gradients has been a topic of major ecological interest. Although relatively well-known, alpha diversity is still poorly understood. It is therefore crucial to investigate alpha diversity patterns as they reveal how diversified species are within a site and identifies processes underlying the co-occurrence of species at a local scale. The patterns and processes related to beta diversity, however, have lagged even more behind. Beta diversity describes the variation in species composition between sites. It reveals whether species turnover or richness differences cause variation in community composition between sites. Together, alpha and beta diversity may provide baseline information for conservation planning, especially in African Tropics. African tropical rainforests, although very diverse, are some of the most threatened and understudied ecosystems of the world. Similarly, although the primary aim in ecology has been to document biodiversity patterns and the processes that structure them, those of invertebrates have lagged behind. As a result, very little is known about African tropical invertebrate patterns and the mechanisms that drive them. The current study, therefore aims (1) describe ant diversity patterns and community assemblages along the Udzungwa mountains, (2) to describe the extent of compositional differences between sites (beta diversity) and (3) to reveal the assembly mechanisms that drive these differences along an altitudinal gradient, Udzungwa Mountains, Tanzania. A standardized pitfall survey was conducted across five elevational transects, each at a distance of 0.1, 1, 20 and 174 km from the first one. Three target elevations which correspond to the three forest types of this mountain (lowland (300-800 m.a.s.l), sub-montane (800-1400), montane (1400-1500)) were selected. A total of 31 776 ant specimens were collected. They belong to five subfamilies, 34 genera and 101 species. Species richness declined with increasing elevation. Three species assemblages corresponding to the three forest types were observed across the mountains. The lowland assemblage was very distinct, while the sub-montane and montane assemblages were closely related. Results show that distance (km) and elevational distance (m.a.s.l) influence variation in community composition (beta diversity). Beta diversity increases with geographic and elevational distance, although more noticeable with elevation. The standardised effect sizes (SES) models suggest that species turnover increases with distance and elevation, while richness differences decrease with distance and elevation. Species turnover plays a significant role in structuring ant communities with increasing elevation while neither species turnover nor richness differences play a significant role in structuring ant communities with increasing geographical distance. The overall findings of this study, therefore, suggest that ants of the Udzungwa mountains are niche conservative, beta diversity is affected by distance and elevation and that species replacement structures ant communities with increasing elevation, while biotic interactions structure ant communities with increasing distance. Therefore, temperature is very important in structuring ant communities along the Udzungwa mountains and complementarity between sites is maximized by choosing sites that are at different elevations.
Ant community responses to fertiliser application and disturbance in a mistbelt grassland, KwaZulu-Natal.
(2021) Khoza, Lindiwe Rebecca.; Munyai, Thinandavha Caswell.; Andersen, Alan N.
Abstract available in PDF.
Ant diversity and composition in a reforested landscape of Buffelsdraai Landfill Conservancy, KwaZulu-Natal.
(2019) Xolo, Sbongiseni.; Munyai, Thinandavha Caswell.; Slotow, Robert Hugh.; Foord, Stefan Hendrik.
Restoration of degraded and reclaimed landscapes provide a useful framework to evaluate the recovery of biodiversity loss. A reforestation project was initiated in 2008 by eThekwini Municipality in Buffelsdraai Landfill Conservancy, aiming to offset carbon emissions over a 20-year period and increase climate change adaptation through biodiversity and ecosystem services restoration. The project offered an opportunity to evaluate to what extent reforestation for carbon sequestration can have co-benefits for biodiversity. The current study monitors the recovery of habitat restoration practices (planting of indigenous forest trees) in Buffelsdraai Landfill Conservancy, eThekwini Municipality, KwaZulu-Natal Province, in South Africa. The main aim of the study was to evaluate how biodiversity recovers following forest restoration. The study used ants (Formicidae: Hymenoptera) as a model organism as they comprise a significant component of invertebrate diversity and a keystone taxon in the terrestrial ecosystems. The study objectives were to provide ant checklist in a reforested landscape and to describe ant diversity patterns along a gradient of restoration and to identify the environmental variables which drive the diversity patterns along a reforestation gradient. Using a standardized pitfall survey, ants were sampled across eight sites, each replicated four times, which included sugarcane (unrestored), grassland and scarp forest (natural reference sites), short-term (0-2 year), medium-term (3-5 years) and long-term (6-8 years) restored sites. Ant sampling was conducted in April-May 2017 (early dry season) and December 2017 (wet season). Environmental (habitat structure) and soil surveys were conducted at each plot. A total of 27 439 ant specimens comprising of 96 species in 31 genera, and six subfamilies were collected. Sample coverage estimator was larger than 0.97, indicating that inventory completion approximated most of the ant assemblages found in the study area. Myrmicinae, Ponerinae and Formicinae were the most abundant and species-rich subfamilies, with Tetramorium, Pheidole and Monomorium as the most species-rich genera. The most numerically dominant species were Pheidole megacephala species group and Anoplolepis custodiens. Ant species richness and activities were significantly highest in the restored and grassland sites and low in forest site, and lowest in unrestored sugarcane. Species richness responded with a hump-shaped response as patterns of species richness significantly decreased with increasing bare-ground cover. High species diversity and composition was associated with open habitats with grass layer. Forest had the most distinct assemblages. Leaf litter, vegetation structure, canopy cover and bare-ground cover, were the four predictor variables which had major influences on ant assemblage structure. Four forest indicator taxa were identified (Pheidole UKZN_11 (megacephala gp.), Tetramorium UKZN_04 (squaminode gp.); Tetramorium UKZN_28 (setigerum gp.) and Leptogenys attenuate), and one indicator for grassland (Lepisiota capensis). No indicators were found for sugarcane sites. Solenopsis UKZN_01 and Pheidole UKZN_09 were potential indicator for restored sites. The restoration sites were transitioning from sugarcane plantation, and were drawing most of their colonisation from grasslands at this stage. This study shows that open woodlands are ideal habitats for maximising species diversity, as they provide a complex habitat for many species, and the availability of local natural grassland as a source of invertebrates assists restoring functioning, even if we expect the community to transition to forest species as regrowth progresses.
Ant diversity, assemblage composition and other arthropod activities in relation to the invader Parthenium hysterophorus L. (Asteraceae) and its biological control agent.
(2022) Hlabisa, Fanelesibonge Samkele.; Munyai, Thinandavha Caswell.; Strathie, Lorraine W.
Invasive alien plants have the potential to alter ecosystem function. While a growing number of studies have focused on the effects of invading plants on native biodiversity and the underlying community dynamics, there is still a lack of studies that detail the impact of invasive plants, such as Parthenium hysterophorus L. (Asteraceae), at higher trophic levels. This study investigated whether P. hysterophorus and its biological control agent, the stem-boring weevil Listronotus setosipennis (Hustache) Coleoptera: Curculionidae, affected ant diversity, assemblages and arthropod activities in the KwaZulu-Natal and Mpumalanga provinces of South Africa. The objectives of this study were to assess the impacts of P. hysterophorus invasion and presence of L. setosipennis on the diversity and assemblage composition of ants, a dominant terrestrial group. Additionally, whether vegetative variables in habitats invaded by P. hysterophorus affected ant assemblages, was examined. Lastly, the study investigated the impacts of the presence and absence of L. setosipennis on other arthropod activities. To study ant diversity and assemblage composition, ants were collected using pitfall traps, over five sampling periods from December 2019 to March 2020, in nine locations around KwaZulu- Natal and Mpumalanga provinces. At each site, three treatments were sampled; viz. P. hysterophorus invaded habitat, P. hysterophorus invaded habitat with L. setosipennis present, and habitat without P. hysterophorus. Species richness and abundance were compared between treatments using ANOVA and the Post-hoc Turkey test. Assemblage composition was analyzed using non-metric multidimensional scaling (NMDS). A Canonical Correspondence Analysis (CCA) was also used to correlate the best environmental variable with ant diversity and assemblage composition. Some 16 463 ant specimens that were collected were identified from four subfamilies, 27 genera, and 55 species. Results indicated that the presence of P. hysterophorus and its biological control agent L. setosipennis did not significantly alter ant diversity, as indicated by species richness and abundance, and assemblage composition, although some differences occurred across locations. The results also showed that vegetative variables (P. hysterophorus height, flowering and cover) did not significantly influence ant assemblages. A separate experiment at six locations in KwaZulu-Natal and Mpumalanga provinces, arthropod activities on P. hysterophorus plants were studied during timed observations at 07h00, 10h00 and 12h00 during monthly sampling from December 2020 to March 2021. Although some arthropod groups were less common visitors to P. hysterophorus than others, this study showed that the presence of L. setosipennis had no significant effect on overall arthropod activities. However, results demonstrated greater activity for some arthropod groups, specifically Hymenopterans, in both treatments, accounting for 60% of all arthropods recorded. Other studies have reported either a positive or negative impact on arthropods by invasive alien plants. These plants may provide a better food resource for native insects and other arthropods, causing them to be attracted to them. However, invasive alien plants have also been linked to a decline in invertebrate species diversity or changes in the composition of populations. This study contributed to growing knowledge on the impacts of invasive alien plants and on terrestrial arthropods, the most prominent group of invertebrates, that are also known to be significant indicators of biological change.
Ant management in Western Cape vineyards.
(2004) Addison, Pia.; Samways, Michael John.
No abstract available.

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