Showing papers by "University of the Witwatersrand published in 1993"

An African Savanna: Synthesis of the Nylsvley Study

Abstract: Savannas cover approximately half of the African land surface and one fifth of the land surface of the world. They are one of the most important, but least understood terrestrial ecosystems. They are the basis of the African livestock industry and the wildlife they support is of key importance in bringing in tourists. The Nylsvley area in South Africa is one of the most intensively studied savanna regions in the world and as such it is a key source of data and theory relating to this important tropical biome. The South African Savanna Biome Programme was set up to develop the understanding necessary to predict changes in the ecosystem stability induced by both natural and man-made stresses. This book provides a synthesis of the programme's sixteen years of research at Nylsvley and aims to develop a unified vision of the ecology of the dry savanna.

The Pleistocene Later Stone Age south of the Limpopo River

Abstract: The earliest Later Stone Age (LSA) industries from southern Africa are microlithic and unstandardized and include the bipolar technique. The dating of these industries is controversial and the earliest microlithic industry is said to occur at Border Cave at about 39,000 B.P. By 18,000 B.P. a bladelet tradition was established and this was replaced in many parts of southern Africa, at about 12,000 B.P., by a widespread and prolific nonmicrolithic industry, characterized by side-struck flakes. The late Pleistocene environment was colder than present, with particularly harsh conditions during the Last Glacial Maximum (LGM), between about 20,000 and 18,000 B.P. Populations may have been isolated because archaeological visibility is low during the LGM and decreases further after the LGM. After 13,000 B.P. there is a dramatic increase in sites and this implies that there may have been widespread colonization of territory previously unoccupied for tens of thousands of years. By the end of the late Pleistocene there was a change in hunting patterns, in parts of southern Africa, from an emphasis on the capture of large, gregarious grazers to an emphasis on small, solitary browsers. Social complexity increased during the late Pleistocene, and by 12,000 B.P. it seems possible that Stone Age people were observing some social practices recorded historically among Bushmen (San).

Erroneous ideas about respiration: The teacher factor

Abstract: Recent research suggests that many South African pupils in their final year of schooling have erroneous ideas about various aspects of respiration (Sanders and Cramer, 1992). This study investigates teachers as a possible source of pupils' errors. The views of 136 biology teachers about respiration and related concepts were elicited by means of an analysis of how teachers marked an essay containing errors commonly found among year-12 pupils. The teachers' responses suggest that many of them might well have erroneous ideas. These are reviewed in terms of four conceptual areas related to respiration. Finally the implications for teachers are discussed, and suggestions are made about possible ways to address the problem of erroneous ideas among teachers and pupils.

Intertrochanteric osteotomy and autogenous bone-grafting for avascular necrosis of the femoral head.

Abstract: A prospective study was done of forty-five hips in forty-three patients who had Ficat stage-III avascular necrosis of the anterosuperior part of the femoral head. The patients had been followed for an average of sixty-five months (range, thirty-six to 126 months) after an operation that included a valgus-flexion intertrochanteric osteotomy, curettage of necrotic bone, and grafting of autogenous bone to the avascular segment. The patients were 32 +/- 8 years old (mean and standard deviation). Patients who were more than forty-five years old, had an underlying systemic disease, had been treated with steroids, had more extensive involvement of the femoral head, or were poorly motivated were excluded from the study. The mean preoperative Harris hip score was 34 +/- 10 points, and the mean score at the most recent assessment was 90 +/- 7 points. Six hips (13 per cent) failed; failure was defined as a Harris hip score of less than 70 points or the performance of a subsequent replacement arthroplasty. Survivorship analysis demonstrated cumulative survival without such failure to be 87 per cent at five years; the ten-year cumulative survival was essentially unchanged. The results of this study suggest that the role of intertrochanteric osteotomy and bone-grafting of the femoral head should be considered anew for the treatment of avascular necrosis of the hip in younger patients who have not received steroids. The results of this procedure should be compared again with those of arthroplasty in the treatment of this condition.

High incidence of the third head of biceps brachii in South African populations.

Abstract: Three different origins were found for the third head of the biceps brachii: (1) an origin from the humeral shaft inferior to and in common with the insertion area for the coracobrachialis; (2) a brachial origin in which the muscle originated distally from the medial humeral shaft, adjacent to and in common with the brachialis muscle; (3) a dual origin in which the medial fibres originated from the short head of biceps and the lateral fibres from the deltoid fascia and the insertion area of this muscle. In all cases, the third head inserted together with the other 2 heads of biceps brachii into the bicipital aponeurosis and the radial tuberosity. The third head receives its innervation from the musculocutaneous nerve, as do the other 2 heads of biceps. When there is a dual origin, partial innervation from the axillary nerve is possible since the fibres of the third head intermingle with those of the deltoid. There was a 20.5% incidence of the third head in South African blacks and only an 8.3% incidence in South African whites. Statistical analysis showed the difference between South African whites and blacks to be significant (P < 0.05). Not all of the blacks, however, had a higher incidence, since the Zulus showed a significant absence (P < 0.05) of the third head when compared with the other black populations.

Sperm competition in frogs: testis size and a ‘sterile male’ experiment on Chiromantis xerampelina (Rhacophoridae)

Abstract: The allometric relationship between body mass and testis mass was calculated using data from 16 genera (37 species) of African and Japanese frogs. Having controlled for body mass, the relative testis mass of Chiromantis xerampelina, Rhacophorus arboreus and R. schlegelli was considerably heavier than predicted (3.8-14.6 times more). All three species have multi-male breeding. Although the result is consistent with sperm competition having selected for increased sperm production in anurans, the phylogenetic distribution of well documented multi-male spawning is confined to the Rhacophoridae. Thus, multi-male mating may have arisen only once effectively reducing the analysis to two data points. However, in the four foam-nesting Rhacophorids whose breeding behaviour has been studied there is also a correlation between relative testis mass and the intensity of sperm competition. This suggests that even within the Rhacophoridae, sperm competition leads to larger testes. Direct evidence for sperm competition in C. xerampelina is provided by a 'sterile male' experiment, which shows that peripheral males are capable of fertilizing eggs.

An automatic S-phase picker

Abstract: An algorithm has been developed for the automatic picking of the S phase from three-component seismic data. Three parameters of the signal are calculated in the program: deflection angle, degree of polarization, and the ratio between transverse energy and total energy. The S phase is declared when the product of the three parameters increases above the reference level. Most parameters are computed automatically and modified if necessary. The S -phase picker is used to analyze data from a local underground mine seismic network.

Creating racial privilege: the origins of South African public health and town planning legislation

Abstract: Town‐planning measures adopted by the infant Union Government were worded in the fashionable new language of international planning and were not explicitly concerned with the regulation of African settlement. Nevertheless, the planning regulations introduced in the 1910s were part of the emerging racial framework of urban government of the South African city. Dr Charles Porter, Johannesburg's first Medical Officer of Health, was a major force behind the introduction of British planning ideas to white South Africa. The inclusion of town‐planning clauses in the 1919 Public Health Act and the 1920 Housing Act were aimed at entrenching urban privileges for whites. By establishing colonial city management standards in selected areas of the city, the position of urban Africans was marginalised. Moreover, the passage of public health and town‐planning laws which prevented overcrowding and rent racketeering and enabled slum rehousing, offered state assistance to unskilled whites. The social and political problems...

Water vapour transport over Southern Africa during wet and dry early and late summer months

Abstract: Southern Africa is semi-arid to arid, and the moisture that contributes to rainfall over the summer rainfall region is largely imported from other areas. Interseasonal and interannual variations in rainfall must result from changes in the circulation and in vapour fluxes over the subcontinent. It is shown that important changes in vapour fluxes occur between October (early summer) and January (late summer), with zonal fluxes being more important in October and meridional fluxes in January. Wet and dry months of October and January are characterized by enhanced zonal (meridional) flow in wet Octobers (Januaries), and reduced importance of these flows in the dry months. Adjustments in the areas of vapour flux convergence and divergence are as important as changes in the fluxes. The convergence and divergence changes between wet and dry months are confirmed by decreases in outgoing longwave radiation over central southern Africa in wet months and increases in dry months. Tropical zonal circulations, and tropical—subtropical meridional circulation cells, conform to the patterns of enhanced (reduced) convection over the central subcontinent in wet (dry) months.

Tissue platelet derived-growth factor (PDGF) predicts for shortened survival and treatment failure in advanced breast cancer

Abstract: In a study of plasma and tissue platelet derived growth factor (PDGF) concentration in patients with breast cancer, elevated levels of plasma PDGF were found in a significant proportion, 11/37 (30%), of patients. Sixteen patients (43%) had tumors which expressed PDGF-AA and 6 patients had tumors which in addition expressed the BB isoform of PDGF. All patients with elevated plasma levels of platelet derived growth factor had tumors which expressed the growth factor on immunohistochemical staining of tumor cells. Furthermore there was a significant correlation between plasma levels of platelet derived growth factor and the intensity of tissue staining. Patients with stage four breast cancer with tumors which were positive for platelet derived growth factor had a significantly lower response rate to chemotherapy as well as significantly shorter duration of survival. In addition, patients with stage four breast cancer who had elevated plasma PDGF levels had a significantly shorter survival. These results indicate that elevated plasma levels of platelet derived growth factor in patients with breast cancer are derived from the tumor cells and suggest that platelet derived growth factor may play a significant role in control tumor cell growth.

Environmental temperature on the vector competence of Culex univittatus (Diptera: Culicidae) for West Nile virus.

Abstract: The effects of the extrinsic incubation temperature on the vector competence of Culex univittatus Theobald for West Nile (WN) virus were studied. A mean titer of 7.0 log10 CPD50/ml of mosquito suspension was reached in orally infected mosquitoes after 11, 15, and 16 d of incubation at 26 and 30 degrees C and at fluctuating temperatures in an outside cage (mean temperature, 23.5 degrees C), respectively. In contrast, 22 and 58 d were required to reach the same titers at 18 and 14 degrees C, respectively. Transmission rates of 100% were reached after 58 d (14 degrees C), 22 d (18 degrees C), and 15 and 16 d (30 degrees C and outside). Except at 30 degrees C, transmission rates fluctuated; e.g., at 18 degrees C from day 19, the transmission rate was 80-100%, whereas at 14 degrees C on day 36, the transmission rate was 60% and thereafter 20-100%. The maximum transmission rate occurred concurrently with maximum titers of virus secreted into capillary tubes during in vitro transmission attempts. Mosquito longevity increased as incubation temperature decreased and was maximum at 114 d at 14 degrees C. Mosquitoes that were transferred from 14 to 26 degrees C after 49 d subsequently oviposited, engorged on a pigeon, and transmitted virus, which indicated the possibility for overwintering of WN virus in adult Cx. univittatus. Vector competence at outside cycling temperatures was intermediate between that at 26 and 30 degrees C, indicating that incubation at 26 degrees C would give a fair reflection of the vector competence of Cx. univittatus during the summer near Johannesburg. Two human epidemics of WN virus are reevaluated in the light of these results; it is concluded that, in addition to abnormal rainfall, higher than normal temperatures were important factors for their occurrence.

Plant distribution in islands of the Okavango Delta, Botswana: determinants and feedback interactions

Abstract: ummary Vegetation on islands in the perennial swamps of the Okavango Delta exhibits a marked zonation pattern. Island fringes are generally characterized by a broadleaf evergreen riparian community of Syzigium cordatum, Ficus verruculosa, F. natalensis, F. sycamorus, Phoenix reclinata, Garcinia livingstonei and Diospyros mespiliformis. This gives way towards island interiors to a community dominated by Acacia nigrescens, Croton megalobotrys and Hyphaene ventricosa. The central regions are characterized either by short, sparse grassland dominated by Sporobolus spicatus or are completely devoid of vegetation with sodium carbonate (trona)-encrusted soil surrounding a central pan of extremely high conductivity. An indirect gradient analysis indicated the important determinants of vegetation distribution as being not only elevation, depth to groundwater and distance from the water source, but also as groundwater chemistry (conductivity and pH) and soil chemistry (sodium concentration). These studies were supported by a direct gradient analysis approach with species tolerances to depth to groundwater, groundwater conductivity and soil-surface sodium concentrations having been established. Feedback interactions of vegetation and groundwater elevation and chemistry, as well as soil chemistry, are evident and appear to be responsible for the vegetation dynamics in the study area. Resume La vegetation des iles dans les marais permanents du delta de l'Okavango presente un schema de zonation marque. Le bord des iles se caracterise generalement par une communaute riveraine a larges feuilles toujours vertes de Sizigium cordatum, Ficus verruculosa, F. natalensis, F. sycamorus, Phoenix reclinata, Garcinia livingstonei et Diospyros mespiliformis. Celle-ci cede le pas vers l'interieur a une communaute dominee par Acacia nigrescens, Croton megalobotrys et Hyphaene ventricosa. Les zones centrales, soit se caracterisent par une prairie courte et clairsemee ou domine Sporobolus spicatus, soit sont completement denuees de toute vegetation, avec un sol encroute de carbonate de soude entourant un centre ou la conductivite est tres elevee. Une analyse indirecte du gradient indiquait que les facteurs determinants pour la distribution de la vegetation ne sont pas seulement la hauteur, la profondeur de la nappe aquifere ou la distance par rapport a une source, mais aussi la composition chimique de l'eau (sa conductivite et son pH) et celle du sol (concentration en sodium). Ces recherches ont ete confirmees par une approche directe de l'analyse du gradient, de la tolerance des especes face a la profondeur de l'eau, sa conductivite et les concentrations en sodium de la surface du sol ayant eteetablies au prealable. Les interactions entre la vegetation d'une part et le niveau et la composition chimique de la nappe aquifere d'autre part, ainsi que celle du sol sont evidentes et semblent etre responsables de la dynamique de la vegetation dans la zone etudiee.

Bone quality: a determinant for certain risk factors for bone fragility.

Abstract: Low bone quantity alone is insufficient cause for fragility fractures. This paper examines the role of bone quality in the fracture risk associated with age, sex, and race. Aspects of bone quality to be considered are bone architecture, matrix, mineralization, and fatigue damage. The trabecular network becomes progressively disconnected and weaker with age. Death of old osteocytes leads to hypermineralization and brittleness of bone. The stability of bone collagen declines with age, and unremodeled bone accumulates fatigue damage. The lower bone fragility rates in males than in females may be due to a combination of the larger male skeleton, greater cortical bone density after age 60 years, and greater bone turnover which would replace fatigue damaged bone. Fragility fracture rates in American and African blacks are lower than in whites, bone mineral density (BMD) is greater in American but not in African blacks (except for hip BMD), and American blacks have lower and African blacks higher bone turnover compared to whites. In South African blacks, trabeculae are thicker and better connected and trabecular bone undergoes less destructive age changes than in whites. To reconcile the disparate findings in American and African blacks we suggest that both groups have a genetic tendency to greater BMD than whites; American blacks realize this potential and African blacks do not, possibly because of calcium deficiency. Consequent high turnover removes fatigue damage and so improves bone quality. Weight-bearing activity in African blacks may be responsible for good hip bone density and thick trabeculae.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative C13 NMR study of polyflavonoid tannin extracts for phenolic polycondensates

Abstract: Assignment of C13 NMR bands to important sites of polymeric flavonoid tannin extracts produced industrially for production of tannin–formaldehyde resins is reported. Five different tannin extracts were studied. The C13 NMR bands' position and relative intensities allowed us to qualitatively explain comparative differences in the five tannins' structural features and properties that are of importance for tannin adhesives applications. The five tannins could be divided into two classes (1) mimosa and quebracho tannins and (2) pecan nut, pine, and gambier tannins. Properties of relevance that varied considerably among the five tannins and that could be detected by 13C NMR were: the relative proportions of fisetinidin/robinetinidin units in relation to catechin/gallocatechin units; differences in number average degree of polymerization; the extent of open heterocycle forms present; branching; and relative proportion of pyrogallol versus catechol B-rings in the flavonoid repeating units. © 1993 John Wiley & Sons, Inc.

Age, size, dominance and reproduction among male kudus: mating enhancement by attrition of rivals

Abstract: Size dimorphism with males larger than females has been related to the benefits for males of enhanced dominance and hence reproductive success. However, mating gains must outweigh the fitness costs of deferred reproduction and the mortality associated with further growth. The relationships between male age, size and reproduction were assessed for greater kudus (Tragelaphus strepsiceros) in the Kruger National Park in South Africa. Individually identifiable animals were monitored over 10 years, with detailed observations made during six breeding seasons. In the non-breeding season males formed loose all-male groups. Horn grappling and low intensity agonistic interactions fostered dominance rankings. Dominance was age-graded, until males reached full weight at 6 years of age. Males aged 6 and 7 years monopolized courtship and mating, but 5-year-old males secured about 10% of mating opportunities. Few males survived beyond 7 years. Male mortality rate rose steeply with age, so that the functional sex ratio of fertile females per mature male was about 14:1. During the breeding season many female groups remained unattended by a mature male. Reproductive sorting among males occurred largely through variation in survival to full size and maturity. Increased size enhances fighting success and hence dominance. Further growth ceases when the functional sex ratio exceeds the number of mating opportunities that males can effectively achieve during a breeding season. Predation amplifies the mortality cost of continued growth. In the absence of large predators, male-male interactions may be atypically exaggerated.

Archean rapakivi granite-anorthosite-rhyolite complex in the Witwatersrand basin hinterland, southern Africa

Abstract: The Gaborone granite suite and the Kanye Formation formed during a single magmatic event in the late Archean evolution of the Kaapvaal craton, southern Africa, and may be the oldest rapakivi granite-anorthosite-rhyolite suite in the world. The Gaborone granite suite underlies an area of >6000 km2 in the northwestern part of the craton and comprises A-type rapakivi granite, leucogranite, granophyric microgranite, and minor anorthosite. It is partly surrounded by the Kanye Formation, a 1000-m-thick pile of pyroclastic and flow-banded rhyolitic lava. Precise U-Pb dating of granitic and granophyric components of the Gaborone suite and rhyolite of the Kanye Formation shows that all three rock types are the same age within error (2783-2785 Ma). Emplaced in the source area during upper Witwatersrand Supergroup sedimentation, the Gaborone-Kanye event has important implications for the tectonic and magmatic evolution of the northern Kaapvaal craton and possibly also played an important role in the development of the adjacent auriferous sediments.