Plant-made therapeutics: an emerging platform in South Africa

The field of plant-made therapeutics in South Africa is well established in the form of exploitation of the country's considerable natural plant diversity, both in the use of native plants in traditional herbal medicines over many centuries, and in the more modern extraction of pharmacologically-active compounds from plants, including those known to traditional healers. In recent years, this has been added to by the use of plants for the stable or transient expression of pharmaceutically-important compounds, largely protein-based biologics and vaccines. South Africa has a well-developed plant biotechnology community, as well as a comprehensive legislative framework for the regulation of the exploitation of local botanic resources, and of genetically-modified organisms. The review explores the investigation of both conventional and recombinant plants for pharmaceutical use in South Africa, as well as describing the relevant legislative and regulatory frameworks. Potential opportunities for national projects, as well as factors limiting biopharming in South Africa are discussed.     

Global soil ciliate (Protozoa, Ciliophora) diversity: a probability-based approach using large sample collections from Africa, Australia and Antarctica

Large sample collections from Africa (92 samples), Australia (157) and Antarctica (90) were investigated for soil ciliates using the non-flooded Petri dish method, which re-activates the ciliates' resting cysts from air-dried samples. Species were determined from life and by silver impregnation. The African samples were the richest, containing 507 species (240 undescribed,=47%), followed by the Australian (361 species, 154=43% undescribed) and the Antarctic (95 species, 14=15% undescribed) samples. The percentage of new species/sample was consistently low, viz. 4–8% on average, indicating that new species were considerably undersampled relative to described ones, very probably due to methodological shortcomings, i.e. usually only cysts of the more euryoecious species could be reactivated. Thus, a probability theory-based statistical approach was applied to the data sets to compensate for the underestimated number of undescribed species. This procedure indicated that, depending on the region, 70–80% of the soil ciliates are still unknown and global soil ciliate diversity amounts to at least 1330–2000 species. Several indicators, especially the constant rate at which new species have been found during a 20-year period of intensive research, suggest that this estimate is conservative. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lake-based climate reconstruction in Africa: progress and challenges

Lake sediments are and will continue to be the principal source of information on the climate history of tropical Africa. However, unequivocal interpretation of the various sedimentological, biological, and geochemical climate-proxy data extracted from lake sediments with respect to past variations in temperature, rainfall, and wind is an extremely complex and challenging exercise. Outstanding problems are: (1) the inherent conflict between a lake's sensitivity to climate change (its ability to respond to and record relatively modest, short-lived climatic anomalies) and its persistence as an archive of climate change (the probability that it survived the most arid events without desiccation or erosion, allowing it to preserve a continuous record of climate history); (2) the scarcity of annually laminated sediment records, which in other regions can provide superior chronological precision to lake-based climate reconstructions; (3) lack of a quantitative (sometimes even qualitative) mechanistic understanding of the chain of cause and effect linking sedimentary climate-proxy indicators to particular climatic variables; and (4) lack of a proxy indicator for past temperature changes unaffected by simultaneous changes in moisture balance. Clearly, a climate-proxy record with high stratigraphic resolution does not represent a high-resolution record of past climate change without demonstration that the sedimentary archive is continuous and undisturbed; that the lake system responds to climate variability at the appropriate time scale; and that any threshold effects in the relationship between the proxy indicator and climate are accounted for. Calibration and validation of climate-proxy indicators is tantamount to establishing accurate reconstructions, but in Africa historical validation of proxy indicators is handicapped by the scarcity of long-term lake-monitoring data. The reliability of lake-based climate reconstructions is enhanced when inferences derived from several proxy indicators (sedimentological, biological, or geochemical), that each have an independent mechanistic link to climate, show a high level of coherence. Given the scarcity of annually-resolved sediment records in tropical Africa, we may have to accept the limitations of ²¹⁰Pb- and ¹⁴C-based chronologies when evaluating the synchrony of reconstructed climate events between sites and regions; however, careful site selection and detailed lithostratigraphic analyses can go a long way to optimise depth-age models and reduce uncertainty in the timing of past climate changes.     

Nationalism,development, and social policy: The politics of nation-building in sub-Saharan Africa

This article examines the relationship between nation-building and social policy in post-independence sub-Saharan Africa (SSA). It argues that post-independence nationalist leaders used health, housing, and education programmes to foster a sense of national unity that would transcend the existing ethnic divisions created by the arbitrary drawing of state boundaries during colonization. Yet, in SSA, the neo-liberal turn of the 1980s favoured the decline of state-level integration and solidarity, which helped trigger territorial mobilization and fragmentation. As a consequence, the politics of welfare retrenchment in SSA does more than simply reduce benefits and increase inequalities; it also potentially weakens national unity.     

Control of onchocerciasis in Africa: threshold shifts, breakpoints and rules for elimination

Control of onchocerciasis in Africa is currently based on annual community-directed treatment with ivermectin (CDTI) which has been assumed to be not efficient enough to bring about elimination. However, elimination has recently been reported to have been achieved by CDTI alone in villages of Senegal and Mali, reviving debate on the eradicability of onchocerciasis in Africa. We investigate the eradicability of onchocerciasis by examining threshold shifts and breakpoints predicted by a stochastic transmission model that has been fitted extensively to data. We show that elimination based on CDTI relies on shifting the threshold biting rate to a level that is higher than the annual biting rate. Breakpoints become relevant in the context of when to stop CDTI. In order for the model to predict a good chance for CDTI to eliminate onchocerciasis, facilitating factors such as the macrofilaricidal effect of ivermectin must be assumed. A chart predicting the minimum efficacy of CDTI required for elimination, dependent on the annual biting rate, is provided. Generalisable recommendations into strategies for the elimination of onchocerciasis are derived, particularly referring to the roles of vectors, the residual infection rate under control, and a low-spreader problem originating from patients with low parasite burdens.     

Stability in a multi-species assemblage of large herbivores in East Africa: an alternative interpretation

Summary Prins and Douglas-Hamilton (1990) analyzed data based on nine census counts of large herbivore species in Lake Manyara National Park, northern Tanzania, over the period 1959–1984. Their major conclusion was that even if individual species-showed large fluctuations in numbers, the different species compensated the fluctuations of the other species in a way resulting in a constancy of total herbivore biomass, constancy of plant biomass consumption, and overall stability of the system under natural conditions. The authors believed that they had found a support for this view by calculating the stability index based on correlations between numbers of large herbivores. In this paper I show that Prins and Douglas-Hamilton's calculation of the stability index was not justified. Grazing and browsing pressure by large herbivores in Lake Manyara National Park seems to be remarkably constant. However, available information does not allow any rigorous conclusions about the stability of this community. We need more data from other systems dominated by large herbivores to be able to make comparisons and to be able to say which systems are more stable and in what sense.     

Freshwater crayfish invasions in South Africa: past,present and potential future

Freshwater crayfish invasions have been studied around the world, but less so in Africa, a continent devoid of native freshwater crayfish. The present study reviews historical and current information on alien freshwater crayfish species introduced into South Africa and aims to indicate which areas are at risk from invasion. As is the case elsewhere, South Africans have shown a keen interest in both farming and keeping freshwater crayfish as pets, which has resulted in Cherax cainii, Cherax destructor, Cherax quadricarinatus and Procambarus clarkii being introduced to the country. There is evidence of successful establishment in the wild for C. quadricarinatus and P. clarkii in different parts of the country. Species distribution models suggest that the eastern part of the country and parts of the Eastern and Western Cape are at higher risk of invasion. At present, illegal translocations represent the most likely pathway of crayfish spread in South Africa. A continued risk of invasion by freshwater crayfish species in South Africa is highlighted, which reinforces the need for more research, as well as for strong mitigation measures, such as stronger policing of existing regulations, management or eradication where feasible and public education.     

Orphanhood and fertility in young adults: Evidence from South Africa

I study the relation between orphanhood and fertility patterns in young adults using a longitudinal survey from the city of Cape Town, South Africa. The data set combines two survey waves with a year-by-year life history calendar that records key outcomes (e.g., schooling, work, fertility). It also provides information on so-called ‘parental investments’ (time and material support), family background, and literacy and numeracy test scores. I find that orphans exhibit significantly higher rates of teenage pregnancy. In particular, teenage motherhood is 19% points more likely among (female) orphans. These results suggest that orphanhood may leave a long-lasting ‘imprint’ in terms of premature fertility, especially in teenage females.     

Creating Grasslands: Social Institutions and Environmental Change in Mkambati Area, South Africa

Through a case study of the grassland system of the Mkambati area in the Eastern Cape, South Africa, the paper explores the interaction of social institutions and ecological processes in the creation of a diverse grassland environment. A number of different transitions between grassland states are examined in detail, highlighting a range of social and institutional factors influencing grassland change. The spatial patterning of different grassland types and the frequency of transitions between them are shown to be dependent on the institutional relationships between different social actors. Understanding such complex and multifaceted processes of environmental change requires analytical tools which combine social and ecological perspectives;an extended form of qualitative state-transition modeling, which incorporates institutional dimensions, is therefore explored.     

The rust mycobiota of southern Africa: Species richness, composition, and affinities

The rust mycobiota (Uredinales, Basidiomycota) of southern Africa (Botswana, Namibia, and South Africa) is analysed with regard to species richness, generic composition, and similarities to the rust mycobiotas of the remaining African continent and other regions of the world. Southern Africa is home to about 546 rust species: ca 522 species have been reported from South Africa, 73 from Namibia, and less than ten from Botswana. Thirty-two species were considered to be exotics. Two hundred and twenty-five of the species are restricted to southern Africa, suggesting an endemism rate of ca 44 %. At present, the rust fungus:host ratio is 1:38.5, which is much lower than expected from other regions of the world. This low ratio may partly be due to under-exploration of the area, but the results presented here indicate that a natural paucity of rust fungi on certain, especially species-rich plant taxa centred in southern Africa and possibly environmental factors are more important reasons. The predominant genera are Puccinia and Uromyces accounting for ca 59 % of the rust species. The genera Hemileia, Phakopsora and especially Ravenelia, centred in tropical regions, are well represented and sum up to 8 % of the species. Members of Melampsoraceae and Phragmidiaceae, common in temperate regions of the Northern Hemisphere, are scarce. Most of the other 28 recorded teleomorph genera are only represented by three or less species. In an African context, most species are shared with central and east Africa (almost 16 %). Only a few species are disjunct between southern and West Africa or Madagascar. Ca 10 % of the species are shared only with other parts of the paleotropics, especially the Indian subcontinent. Disjunctions of native species with the New World, Australia/New Zealand, or Europe are rare.     

Refugia, dispersal and divergence in a forest archipelago: a study of Streptocarpus in eastern South Africa

We describe a scenario of plant speciation across a relict forest archipelago in South Africa involving Pleistocene habitat expansion-contraction cycles, dispersal and adaptation to lower temperatures. This is the first population level study using molecular data in South African forests and has significant implications for conservation efforts in this area. Populations of the mesophytic forest floor herbs Streptocarpus primulifolius sensu lato and Streptocarpus rexii were sampled throughout their range in the naturally fragmented forests of eastern South Africa in order to investigate population genetic and phylogenetic patterns within the species complex, using nuclear microsatellites, nuclear ribosomal ITS (internal transcribed spacer) sequences and chloroplast genome sequences. S. primulifolius harbours high levels of genetic diversity at both the nuclear (mean HE = 0.50) and the chloroplast level (each population fixed for a unique haplotype). This is consistent with populations of these coastal species being Pleistocene relicts. In contrast, populations of S. rexii in cooler habitats at higher altitudes and lower latitudes harbour little or no nuclear genetic diversity (mean HE = 0.09) and most share a common chloroplast haplotype. The split of S. rexii from populations intermediate between the two species (S. cf. primulifolius) occurred between 0 and 0.44 million years ago according to the calibrated ITS phylogeny of the taxa. The low genetic diversity and homogeneity of S. rexii is congruent with this species having reached its current range during the Holocene. We found no evidence of monophyly of any of the taxa in this study, which we consider a consequence of recent evolution in a fragmented habitat.     

Last Interglacial Hominid and Associated Vertebrate Fossil Trackways in Coastal Eolianites,South Africa

Two Late Pleistocene hominid footprint sites are known in South Africa, one on the west coast (Langebaan) and the other on the southeast coast (Nahoon). Both trackways occur in calcareous eolianites and are dated to the Last Interglacial (～120 ka). The chief objective is to infer anatomical features of these early anatomically modern hominid footprint makers, about which little is known. At Nahoon, trackways of at least five species of vertebrates, including three hominid footprints, are preserved as casts. One footprint preserves excellent detail, appearing in all respects to be modern, but possibly with a deformity of the small toe. The impressions are shallow and suggest slight build. The stature of the footprint maker, as estimated from foot length (19.2 cm), is ～127 cm, considerably less than modern adult Khoi-San and was probably made by a juvenile. The step length is short relative to foot length, a consequence of walking uphill on a yielding substrate. The Langebaan trackway (preserved as natural impressions) comprises two intact prints and remnants of a third. Pronounced push up mounds flank the prints and preservation of toe impressions is poor. The foot length is 22.8 cm, indicating a stature of ～1.57 m. This falls within the range of modern adult Khoi-San, lending some support to the notion that Middle Stone Age people were of small stature. The depth of the prints and clumsy progression are suggestive of heavy build.     

Tectonics, orbital forcing, global climate change, and human evolution in Africa: introduction to the African paleoclimate special volume

The late Cenozoic climate of Africa is a critical component for understanding human evolution. African climate is controlled by major tectonic changes, global climate transitions, and local variations in orbital forcing. We introduce the special African Paleoclimate Issue of the Journal of Human Evolution by providing a background for and synthesis of the latest work relating to the environmental context for human evolution. Records presented in this special issue suggest that the regional tectonics, appearance of C(4) plants in East Africa, and late Cenozoic global cooling combined to produce a long-term drying trend in East Africa. Of particular importance is the uplift associated with the East African Rift Valley formation, which altered wind flow patterns from a more zonal to more meridinal direction. Results in this volume suggest a marked difference in the climate history of southern and eastern Africa, though both are clearly influenced by the major global climate thresholds crossed in the last 3 million years. Papers in this volume present lake, speleothem, and marine paleoclimate records showing that the East African long-term drying trend is punctuated by episodes of short, alternating periods of extreme wetness and aridity. These periods of extreme climate variability are characterized by the precession-forced appearance and disappearance of large, deep lakes in the East African Rift Valley and paralleled by low and high wind-driven dust loads reaching the adjacent ocean basins. Dating of these records show that over the last 3 million years such periods only occur at the times of major global climatic transitions, such as the intensification of Northern Hemisphere Glaciation (2.7-2.5 Ma), intensification of the Walker Circulation (1.9-1.7 Ma), and the Mid-Pleistocene Revolution (1-0.7 Ma). Authors in this volume suggest this onset occurs as high latitude forcing in both Hemispheres compresses the Intertropical Convergence Zone so that East Africa becomes locally sensitive to precessional forcing, resulting in rapid shifts from wet to dry conditions. These periods of extreme climate variability may have provided a catalyst for evolutionary change and driven key speciation and dispersal events amongst mammals and hominins in Africa. In particular, hominin species seem to differentially originate and go extinct during periods of extreme climate variability. Results presented in this volume may represent the basis of a new theory of early human evolution in Africa.     

Disturbances in semi-arid shrubland and arid grassland in the Karoo, South Africa: mammal diggings as germination sites

Mammals (mainly aardvark Orycteropus ufer , porcupine Hystrix austro-africanae , bat-eared fox Otocyon megalotis and Cape fox Vulpes chama ) which excavate holes in hard-capped soils in Karoo shrubland and inter-dune pans create microsites where seeds, detritus and water accumulate, and seeds germinate. Holes with seedlings were significantly deeper (6.7 ± 0.4 cm) than holes without seedlings (4.5 ± 0.3 cm). In open, inter-shrub sites, significantly more seedlings germinated in diggings than on the flat soil surface, but there was no difference in the proportion of seedlings germinating under shrubs and in diggings. In inter-dune pans, 96% of all seedlings found were growing in diggings.

Résumé

Les mammifères (surtout l'oryctérope Orycreropus afer , le porcépic Hystrix austro-ajricanae , l'otocyon Otocyion megalotis , et le renard du Cap Vulpes chama ) qui creusent des trous dans les régions buissonneuses du Karoo et dans les creux entre les dunes créent des microsites où les semences, les déchets et l'eau se rassemblent, et les semences germent. Les trous où elles germent sont significativement plus profonds (6,7 ± 0,4 cm) que ceux où elles ne germent pas (4,5± 0,3 cm). Aux endroits buissonneux ouverts, il pousse plus de jeunes plantes dans des creux qu'à la surface du sol, mais il n'y a pas de différence entre les proportions de celles qui poussent sous les buissons et dans les creux. Dans les creux entre les dunes, 96% des jeunes pousses croissent dans les excavations.     

The past, present and future of childhood malaria mortality in Africa

During the past few years, there has been a historic series of declarations of renewed commitment to malaria control in Africa. Whether the burden of malaria is increasing in Africa is a moot point. This article attempts to re-construct the evidence for the trends in childhood mortality as a result of Plasmodium falciparum infection over the last century in Africa.