School of Life 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.
Accretion versus bioerosion on the Maputaland reefs in South Africa - The major processes.
(2011) Grimmer, Ashley.; Schleyer, Michael H.; Glassom, David.
The development of coral reefs is largely restricted to areas within the tropics where favourable conditions for both coral and reef growth prevail. There is, however, a continuum from these typical, accretive reefs in the tropics to marginal, non-accretive, coral-dominated reef communities which occur at higher latitudes. High-latitude reefs function similarly in many regards to their tropical counterparts and are regulated by similar processes to a varying degree. In this study, the major biological and physico-chemical processes were assessed which directly or indirectly prevent the continued persistence of reefal frameworks and thus hinder reef accretion on high-latitude reefs in the iSimangaliso Wetland Park. These reefs have a high diversity of hard and soft corals with significant reef coverage, yet little evidence of any biogenic accretion has been observed. The scleractinian coral, Acropora austera, is one of the few corals which may be responsible for reef framework production. It exhibits a gregarious growth pattern, forming large, monospecific stands with an interlocking framework characteristic of the early stages of reef accretion. The framebuilding potential of A. austera and the continued persistence of such frameworks were thus determined by in situ monitoring of coral growth, mortality, bioerosion and several physico-chemical parameters. Growth rate and mortality of A. austera branches were measured at three sites of differing stand size and apparent age. This was achieved by repeated image analysis and by staining branches with the vital stain, Alizarin Red S. Both measures of growth yielded a similar linear extension rate of 24.5 mm/yr (n = 467), comparable to related species at similar latitudes. Mean branch mortality was as high as 50%, with clear differences manifested between each A. austera stand. Branch extension rates and branch mortality were inversely related between sites. Small, young stands exhibited significantly faster coral growth rates, lower mortality and a net increase in overall branch length over the study period, whilst the opposite was true of larger, more developed stands. In addition, bioerosion was determined at each site to assess its potential for carbonate removal and its destabilizing effect on reef frameworks. Bioerosion intensity was recorded as “percentage area damage” within cross-sections and “frequency of occurrence” of bioeroding organisms in coral rubble fragments (n = 120). The level of bioerosion was found to be substantial (up to 11.5% loss in weight of coral fragments over the 12-month study period) and was found to decrease significantly with a reduction in size of each A. austera stand. Aragonite saturation state is considered a major factor that limits the geographical range of coral reefs globally. Although previously thought to be limiting in Maputaland, mean ΩArag values of 4.40±0.29 were measured on the reefs in summer and 4.33±0.21 in winter and thus would not have limited reef development. Past studies have noted the turbulence on South African east coast reefs and its adverse effect on reef development. This was corroborated in this study with the measurement of considerable sediment re-suspension (0.17 g cm⁻² day⁻¹) and regular damage to both living coral and the reef framework caused by large swells. These results lead to the theory that Acropora austera stands senesce with increasing size and age. Although large coral frameworks are found on the Maputaland reefs, they do not persist in the long term. High rates of sediment re-suspension prevent infilling of the interstitial spaces and eventual cementation, while high levels of bioerosion lead to framework instability over time. Rough seas further hamper accretion by physical removal of both living coral and the coral-derived framework, thus removing recent growth. This process is suspected to cause an imbalance in the carbonate budget of these marginal reefs, ultimately favoring carbonate removal over carbonate deposition.
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.
Adhension of Candida albicans to host cells in culutre.
(1989) Maiter, Aziza Ismail.; Alexander, D. M.; Oellermann, Rolf Alfred.
No abstract available.
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.
Aerobic utilization of selected pharmaceutical and personal care product by estuarine heterotrophic bacteria.
(2014) Bulannga, Rendani Bridghette.; Schmidt, Stefan.
Pharmaceutical and personal care products (PPCPs) constitute a broad class of organic compounds, some of which belong to the list of the OECD high production volume (HPV) chemicals. These compounds have emerged as environmental contaminants with potentially detrimental effects. They have been detected in various environmental compartments typically in a nano- to microgram range and sewage treatment plants represent the major point source for the aquatic environment. Salicylic acid, a monohydroxybenzoic acid, is widely used in cosmetic and therapeutic products and is listed as HPV chemical. Benzyl salicylate and phenyl salicylate are diaryl ester compounds commonly used in pharmaceutical formulations, fragrances and household detergents. Benzyl salicylate is listed as HPV chemical. The fate of salicylic acid in the environment has been reported previously while those of benzyl salicylate and phenyl salicylate are unknown. Although studies are available on the microbial degradation of aromatic compounds, studies exclusive to the catabolism of PPCPs by marine heterotrophic bacterial isolates are rather limited. Therefore, the aim of this thesis was to characterize PPCPs (salicylic acid, benzyl salicylate and phenyl salicylate) utilizing bacteria from an estuarine environment (Durban Harbour, KwaZulu-Natal, South Africa). Selective enrichments were employed using artificial seawater medium typically supplemented with 2 mM of the target compounds (salicylic, benzyl salicylate or phenyl salicylate). After successive subculturing, bacteria capable of utilizing target compounds as sole carbon and energy source were characterized by morphological and physiological features, 16S rRNA gene sequence and MALDI-TOF MS analysis. Growth kinetics were assessed by monitoring the optical density, cell count and protein formation over time. The utilization of salicylic acid and phenyl salicylate was verified using UV spectroscopy and HPLC and the key reactions involved were verified by determining the specific oxygen uptake rates using resting cells and specific activities of representative enzymes. A Gram-negative coccus shaped bacterium belonging to the genus Acinetobacter degrading salicylic acid and phenyl salicylate, a Gram-negative rod shaped marine bacterium belonging to the genus Oceanimonas degrading salicylic acid and phenyl salicylate and a Gram-negative rod shaped bacterium belonging to the genus Pseudomonas utilizing benzyl salicylate in the presence and absence of synthetic surfactants (Tween 80) were isolated. The growth of Acinetobacter and Oceanimonas species was dependent on salicylic acid and phenyl salicylate as carbon source as growth was only observed when the carbon source was present and the compound was degraded almost to completion. Growth of Pseudomonas with benzyl salicylate was enhanced in the presence of surfactant. All three strains did not have an obligate requirement for NaCl. Acinetobacter and Oceanimonas strains were tolerant to high concentrations of salicylic acid and were inhibited at a concentration above 20 mM while phenyl salicylate did not show toxic effects on the strains; instead growth increased with the increase in concentration. Salicylic acid was utilized via catechol by both strains as they showed high specific oxygen uptake rates and catechol-1, 2-dioxygenase activity for this chemical. Phenyl salicylate was hydrolyzed at the ester bond to phenol and salicylic acid, as these were the metabolites that accumulated during growth with phenyl salicylate. The mono-aromatic metabolites resulting from the hydrolysis of diaryl substrate were further metabolized via catechol. Microbial catabolic activities were solely responsible for the loss of contaminant in the medium as confirmed by abiotic controls. Heterotrophic bacteria can therefore play an important role in the removal of contaminants from marine environments.
Age and growth of the Queen Mackerel (Scomberomorus plurilineatus) and Seventy-four (Polysteganus undulosus) of KwaZulu Natal, South Africa.
(1996) Chale-Matsau, Jacobeth R.; Beckley, Lynnath E.; Govender, Anesh.
This study provides information on the age and growth of two important Iinefish species, Scomberomorus pluriline~tus and Polysteganus undulosus. Age determination for both species was carried out using otoliths and growth was modelled using age- and length-based methods. For the age-based method various growth models were evaluated to determine which growth function best described the age-length data, whilst Shepherd's Length Composition Analysis was used to estimate growth parameters from length-frequency data. Preliminary stock assessments, based on limited catch data, were also attempted for both species. Age estimates for the pelagic migrant S. plurilineatus, derived from reading whole otoliths, ranged from 0 + to 6 + years. As validation by marginal increment analysis was inconclusive because of the seasonal occurrence of this species in KwaZulu-Natal waters, it was assumed that a single opaque band was laid down in the otolith annually. Reproducibility of age estimates evaluated using the average percentage error (APE) technique was good (9.4%). Von Bertalanffy growth parameters were poorly estimated from length-frequency data because multiple maxima were encountered on the fitting surface. However, from the age-length data, growth was adequately modelled by the von Bertalanffy growth equation: L t =9 3 5mmFL (l-e -0. 583yr-1 (t+o. 991yr) ) S. p!urilineatus are fully recruited to the fishery at the age of 1 + year and the ageiv at-50% maturity is 2 + years. Preliminary per-recruit analyses indicated that the spawner biomass of S. plurilineatus is at 50% of its unfished level. Polysteganus undulosus is an endemic, reef-dwelling sparid and large catches weremade earlier in the century. Age determination was carried out using sectioned otoliths collected in 1962 and 1963 before the collapse of the fishery. Age estimates ranged from 3 + to 20 + years. Marginal increment analysis indicated that active deposition of opaque bands occurred during winter but, because of the seasonal occurrence of P. undulosus in KwaZulu-Natal, validation was inconclusive. Reproducibility of the age estimates was low (APE = 18.2%) because of difficulties with band interpretation as a result of stacking on otolith margins in old fish. Von Bertalanffy growth parameters could not be adequately estimated from length frequency data because of the slow growth and longevity of this species. However, from the age-length data, no difference in growth rate between the sexes was observed, and growth for the combined sexes is described by the following logistic equation: L = 942mmTL t 1+e-O.277yr-l(t-S.178yrs) The age at full recruitment was found to be 12 + years and the age-at-50% maturity was 8.8 years. A preliminary stock assessment revealed that the spawner biomass of P. undulosus was already at 25% of its unfished level in the early 1960s.
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.
Alkalic salt-based pretreatment strategies for enhancing sugar recovery from corn cobs and process development for simultaneous saccharification and bioethanol production.
(2018) Sewsynker-Sukai, Yeshona.; Gueguim Kana, Evariste Bosco .
Abstract available in PDF file
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.
Altitudinal and seasonal variation in amethyst sunbird physiology.
(2007) Lindsay, Claire Vicky.; Downs, Colleen Thelma.; Brown, Mark.
Southern Africa is characterised by an unpredictable environment with daily and seasonal temperature fluctuations. As a local or non-migratory endothermic species occurring over an altitudinal gradient from the Drakensberg to the coast of KwaZulu- Natal in southern Africa, Amethyst Sunbirds (Chalcomitra amethystina) experience challenging thermal conditions and increased energetic stress as a result of ambient temperature variation. Flexibility of metabolic rates within a species allows for the colonization of different habitats along an altitudinal and thus temperature gradient. It was predicted that over this altitudinal gradient Amethyst Sunbirds would exhibit variation in metabolic rates, particularly basal metabolic rates, pre- and postacclimation, as well as variation in hematocrit levels in winter and summer trials. It was also predicted that Amethyst Sunbirds would exhibit seasonal variation in metabolic parameters. Sunbirds were caught in a winter and summer season (2006-2007) using mist nets in three locations; Underberg (1553 m), Howick (1075 m) and Oribi Gorge (541 m). Upon capture, metabolic rate was measured indirectly by quantifying oxygen consumption (VO2) using flow through respirometry, at 5 and 25°C. Birds were then acclimated at 25°C for 6 weeks on a 12L:12D cycle. VO2 was measured postacclimation at 8 different temperatures (15, 5, 10, 20, 30, 28, 25 and 33°C). Hematocrit levels were taken pre-acclimation and pre-release. Winter and summer data were compared. In the winter trials it was found that there was little variation in VO2 between individuals from the same locality, whereas significant variation was observed at the same temperatures between localities and thus between altitudes. The subpopulation from the highest altitudinal site had the highest basal metabolic rate (BMR). Summer trials showed that metabolic rates did not differ significantly between altitudinal subpopulations of Amethyst Sunbirds, however, BMR was observed to decrease as altitude decreased. The comparison of seasonal data showed that Amethyst Sunbird subpopulations from Underberg and Howick showed higher post-acclimation VO2 values per temperature in winter than in summer trials. Post-acclimation resting metabolic rate (RMR) values for Howick subpopulations were generally higher in winter than in summer, Underberg Amethyst Sunbirds showed a significant difference between summer and winter RMR at 5 and 10°C and Howick sunbirds showed a significant difference in RMR between seasons at 5°C. The Oribi Gorge subpopulation, however, showed no significant differences in metabolic rate between any temperatures when comparing a summer and a winter season. Thermal neutral zones of all of the subpopulations of Amethyst Sunbirds shifted between the winter and summer trial period. This study thus emphasized the need to understand plasticity in metabolic rates and acknowledge altitudinal and seasonal differences within a species, in order to make accurate predictions about a species thermal physiology and responses to changes in ambient temperatures. In particular, the variation in BMR, which is usually used as a species specific value, should be acknowledged in comparative studies of avian metabolic rates or in climate change models.
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.
An evaluation of present and potential inland fisheries in dams and rivers in the uThukela and uMngeni Catchments, KwaZulu-Natal, South Africa.
(2024) Makhathini, Ntandokayise.; Downs, Colleen Thelma.
Globally, freshwater systems and their biodiversity and ecosystem services are threatened. Freshwater fisheries in South Africa are understudied despite their economic importance to fishers, especially subsistence fishers. Little is known about the potential for rivers and impoundments to support subsistent fisheries and the resilience of native fish species impacted by invasive alien fish species. The main aim of this study was to address the lack of knowledge about economically and biologically important indigenous fish species that support inland fisheries in KwaZulu-Natal Province, South Africa. The composition and contribution of native and invasive fish species and their offtake by fishers were assessed. Fishers across the uThukela and uMngeni catchments were interviewed using in-person questionnaires. In addition, assessment of fish communities and population structures in Midmar Dam and Henley Dam, two selected dams on the uMngeni River, coupled with questionnaire data, were used to determine the offtake trends by fishers (subsistence and recreational). These will contribute to a potential subsistence fisheries management plan for these dams based on the findings to guide the development of the provincial and national inland fisheries plan. Firstly, in a systematic review, the present and potential inland fisheries in dams and rivers across Africa to guide inland fisheries in KwaZulu-Natal, South Africa, were assessed. The results showed diverse inland fisheries types with distinct characteristics and shared challenges. National and regional importance of African inland fisheries was found, but there was a lack of understanding of the definitions and boundaries between the categories of inland fisheries. Subsistence fisheries, focusing on local food provision through traditional methods, face threats like overfishing. Recreational fisheries, contributing to food, income, and recreation, require effective conservation in developing nations. Small-scale fisheries showcase resilience and successful conservation, emphasising adaptive management. Commercial fisheries involving professional fish exploitation encounter challenges, especially in regions like South Africa, demanding sophisticated approaches for long-term viability. Across Africa, common challenges such as overfishing and habitat destruction persist. In KwaZulu-Natal, a significant research gap exists, impacting sustainability. Addressing issues like monitoring systems, invasive species, and species knowledge is crucial for sustainable fisheries management in the region. Secondly, to address the paucity of knowledge of economically beneficial fish species and their offtake based on the perceptions of fishers present in selected sections of the uMngeni and uThukela catchments, KwaZulu-Natal, South Africa, a questionnaire interview method was used to obtain fishers' responses during 2021-2023. Findings from this study revealed difficulties in categorising fishers because of present inland water policies similar to the “fuzzy boundary” concept for inland fisheries globally, with some individuals identifying as recreational because of nondisclosure fears. Fishers’ knowledge illustrated the ecological imbalances between native (Labeobarbus natalensis) and invasive (Cyprinus carpio, Micropterus spp.) species, as well as the economic importance of fish based on market valuations, with C. carpio having a greater market value. Additionally, the results showed that subsistence fishers preferred river fishing compared with recreational fishers that targeted impoundments. Importantly, a considerable percentage of subsistence fishers ate fish mostly once a week or once a month. These results highlighted the importance of holistic management of water regulations, fish ecology, and economics to promote sustainable inland fisheries. Thirdly, an ecological assessment of fish communities in Midmar Dam and Henley Dam during the winter and summer seasons of 2022 and 2023 was conducted. Diverse fishing methods were used to capture a broad spectrum of fish species. Additionally, questionnaires were administered in selected areas of KwaZulu-Natal to gather complementary data on fish species in inland fisheries. A total of six fish species (three native species and three invasive species) were found in the two impoundments. Midmar Dam had significantly higher total fish catch than Henley Dam, highlighting the role of environmental factors such as dam size, depth, and temperature in shaping fish populations and influencing overall productivity. The KwaZulu-Natal yellowfish (L. natalensis) was significant to local inland fisheries, while invasive fish species posed challenges to maintaining the native fish species. These results emphasised that incorporating fish catch data into decision-making processes is crucial for making informed, science-based choices that ensure the long-term viability of fish populations and promote the overall health of freshwater ecosystems. In conclusion, the findings underscore the necessity for tailored fisheries management strategies that consider the unique environmental characteristics of each dam and the structures of fish populations. By integrating water quality data, catch-per-unit-effort (CPUE) results, and insights from fishers, decision-makers can formulate science-based approaches to preserve fish populations, support local livelihoods, and safeguard vulnerable communities dependent on subsistence fishing. Ultimately, successful conservation and sustainable management of fish populations hinge on informed decision-making prioritising ecosystem health and resilience across KwaZulu-Natal's freshwater habitats.
Analyses of lipidic bodies from green microalgae.
(2014) Pather, Verushka.; Gupthar, Abindra Supersad.; Bux, Faizal.
This study presents the analyses of oil body components in microalgae which may be involved in oil droplet assembly including certain triacylglycerol precursors which can be processed to biodiesel, an alternative fuel source. Stress induction of microalgae, Chlorella vulgaris CCAP 211/11B and Dunaliella primolecta CCAP 11/34 was achieved by exclusion of nitrates in growth media. Contrary to other forms of nitrogen depletion, this condition did not greatly enhance lipid biosynthesis in the microalgae. Confocal microscopy and fluorescent dyes nile red and bodipy were employed for the visualization of lipidic body components. The fluorescence hues emitted by neutral lipids and phospholipids were differentiated from those due to autofluorescence and chlorophyll using ZEN software to analyse images from a Zeiss LSM 710 confocal microscope. Oil from both algae, which were subjected to transesterification and gas chromatography, revealed a predominant fatty acid, namely palmitic acid (C16:0). D. primolecta produced linolelaidic acid (C18:2n6t) under growth conditions involving both nitrate supplementation and exclusion; whilst the longest fatty acid, docosanoic acid (C22:0 chain) was produced by the alga C. vulgaris only under conditions of nitrate supplementation. Nitrate limitation had minimal effect on the oil hydrocarbon yield which increased only 0.02% and 0.01% for C. vulgaris and D. primolecta, respectively. The highest biodiesel yield of 26.11 % was recorded from D. primolecta when grown under conditions of nitrate exclusion. The protein concentrations extracted from oil of the former alga ranged from 1.87 - 1.95 Gg/ml when grown under nitrate supplemented conditions and 1.74 - 1.90 Gg/ml when nitrate was excluded from the media. The protein concentrations extracted from oil of D. primolecta ranged from 1.91 - 2.23 Gg/ml and 1.88 - 1.98 Gg/ml, respectively, when the algae were grown in the presence and exclusion of nitrates. In the adaptation of protocols for protein extraction from oil, sunflower and salmon oils were initially used. Sunflower oil extracts produced by 10% (w/v) SDS treatment, yielded protein bands of 198, 96, 70 and 58 KDa on 10% (w/v) polyacrylamide gels while 6M urea treatment yielded a band of 200 KDa. Salmon oil treated with 10% (w/v) SDS and 6 M urea yielded bands of 195 and 27 KDa, and 198 KDa, respectively, as well as common bands of 68 and 64 KDa. In comparison, the extraction of discrete proteins from algal oil proved to be difficult as the extractants SDS and urea could have denatured protein components into subunit structure.
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.

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