Scielo RSS <![CDATA[South African Journal of Science]]> http://www.scielo.org.za/rss.php?pid=0038-235320080002&lang=en vol. 104 num. 3-4 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Alternatives to the publication subsidy for research funding</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200001&lng=en&nrm=iso&tlng=en <![CDATA[<b>Botanical research in South Africa</b>: <b>a questionnaire assessment of opinions of South African botanists</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200002&lng=en&nrm=iso&tlng=en <![CDATA[<B>The seminal legacy of the Southern African Bird Atlas Project</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200003&lng=en&nrm=iso&tlng=en The first Southern African Bird Atlas Project Project was launched in 1986 and gathered bird distribution data from six countries of southern Africa. The project culminated with the publication of The Atlas of Southern African Birds in 1997. The database generated by the project, seven million bird distribution records, has been widely used by four groups: environmental consultants (for example, to locate electricity transmission lines), conservationists (planning conservation strategies), research scientists (especially macro-ecologists and biogeographers) and birders (ecotourism materials). By 2007, the database had spawned 50 research publications and eight Ph.D.s and master's degrees. These products are a tribute to the more than 5000 'citizen scientists', who gathered the bulk of the data. The atlas concept has been extended to frogs, reptiles, spiders and butterflies; a second bird atlas started in 2007 and will, for example, facilitate knowledge of the impact of environmental change on birds. The South African National Biodiversity Institute is playing a lead role in initiating these new projects. <![CDATA[<B>Postharvest disinfestation treatments for deciduous and citrus fruits of the Western Cape, South Africa</B>: <B>a database analysis</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200004&lng=en&nrm=iso&tlng=en Effective postharvest disinfestation of export fruits from the Western Cape province of South Africa would help to reduce rejections due to the presence of insects. However, there is normally only a limited opportunity between controlling the insects and damaging the produce. A widely used agent in disinfestation procedures, methyl bromide, was scheduled to be withdrawn in many countries in 2005 due to its ozone-depleting properties. The main alternatives are irradiation, extreme temperatures, forced air, vapour-heat methods and the use of controlled atmospheres. A literature survey was used to identify postharvest treatments with the highest likelihood of success in killing insect contaminants without damaging the fruit. Data from 284 scientific articles relating to these kinds of disinfestation were entered into a database (PQUAD). Queries were run to determine the most intensively studied fruits and pests. The tolerances of the commodities were compared with those of the pests at family level. Where pest tolerances were lower than those of the fruit, the treatment was regarded as a possible candidate for use. Methyl bromide, controlled atmospheres and irradiation were identified as the most widely used against pests. Irradiation appeared to control insects at doses that did not damage deciduous produce. Citrus appeared to be more susceptible to damage, however, than deciduous fruits. Low temperature also seemed to be less detrimental to deciduous fruit than to citrus. Deciduous fruit is already preserved in cold storage, making this an inexpensive option to combat insects. Cold treatment appeared to control members of the Pseudococcidae, Tephritidae and Tortricidae; more work is required on the other pest families. Controlled atmospheres also had a high chance of success for both citrus and deciduous fruits. <![CDATA[<B>Life-history evolution as an explanation for the absence of the tree life-form in Cape fynbos</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200005&lng=en&nrm=iso&tlng=en Invasive exotic tress are able to grow tall (more than 15 m) in the fynbos environment of the southwestern Cape of South Africa, whereas the tallest fynbos plants, generally from the Proteaceae, have much shorter maximum stature (less than 5 m). Analysis of the Protea Atlas Database for the Cape shows a positive correlation between age at maturity and maximum plant size. Monographs of the Proteaceae indicate a shorter period to maturity for reseeders than resprouters. We propose an evolutionary hypothesis for the absence of trees in the fynbos; predictable, frequent fires have favoured early maturity and this has discriminated against any strategies with delays to maturity (such as experienced by resprouters and trees). <![CDATA[<b>Sexual dimorphism in the mandible of indigenous South Africans</b>: <b>a geometric morphometric approach</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200006&lng=en&nrm=iso&tlng=en We report here on analyses of new landmark data which capture the range of variation in the expression and magnitude of mandibular sexual dimorphism in adult South African Bantu-speaking individuals. The sample examined, separately and pooled, comprises 225 (120 male and 105 female) individuals of known sex representing five local populations: Zulu, Swazi, Xhosa, Sotho and Tswana. Thirty-eight bilateral three-dimensional landmarks were acquired using a Microscribe G2X digitizer and were analysed using geometric morphometric methods. Multivariate statistics were applied to visualize the pattern, and assess the significance, of shape variation between the sexes. All samples demonstrate highly significant size and shape dimorphism, the condyle and ramus consistently being the most dimorphic region of the mandible. Our results also indicate that the mandible of individuals from this population is just as dimorphic, if not more so, than the cranium alone. <![CDATA[<B>A reconstruction of the Cape (South African) fur seal harvest 1653-1899 and a comparison with the 20th-century harvest</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200007&lng=en&nrm=iso&tlng=en The Cape fur seal was an abundant resource in southern Africa, when first discovered by itinerant sailing vessels in the late 16th century. Seals were slaughtered indiscriminately by the sailors for skins, meat and oil for three centuries from around 1600 to 1899. Government controls over the sealing industry were first introduced as late as 1893, by which time at least 23 seal colonies had become extinct and the seal population had been significantly reduced. This paper reconstructs the historical seal harvest from the time of arrival of the first settlers in 1652 up to 1899. These data are then compared with modern harvest data from 1900 to 2000, illustrating the marked increase in the harvest from about 1950, and the concomitant recovery of the seal population to a level of around 1.5-2 million animals. <![CDATA[<B>The feasibility and implications of nuclear georeactors in Earth's core-mantle boundary region</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200008&lng=en&nrm=iso&tlng=en We examine the likelihood and geochemical consequences of the existence of nuclear georeactors in the core-mantle boundary region (CMB) between the Earth's silicate mantle and metallic core. Current geochemical models for the Earth's interior predict that U and Th in the CMB are concentrated exclusively in the mineral calcium silicate perovskite (CaPv), leading to predictable concentration levels of approximately 12 ppm U + Th, 4.5 Ga ago assuming that CaPv is distributed evenly throughout the CMB. Assumption of a similar behaviour for primordial 244Pu provides a substantial flux of neutrons from spontaneous fission. We show that an additional concentration factor of only an order of magnitude is required both to initiate and maintain self-sustaining nuclear georeactors based on fast fission. Continuously operating georeactors with a power of 5 TW (1 TW = 10(12) W) can account for the observed isotopic compositions of helium and xenon in the Earth's mantle. Our hypothesis requires the presence of elevated concentrations of U and Th in the CMB, and is amenable to testing by direction-sensitive geoneutrino tomography. <![CDATA[<B>Polarization mode dispersion compensation for the South African optical-fibre telecommunication network</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200009&lng=en&nrm=iso&tlng=en Polarization mode dispersion (PMD) is worldwide a major obstacle in the successful implementation of next-generation optical-fibre telecommunication networks. Countrywide PMD measurement results are presented which illustrate the extent of the PMD problem in the South African network. An analysis of these results highlights the urgent need for a suitable intervention strategy such as PMD compensation if the South African network is to operate extensively at 10 Gb/s and beyond. The effectiveness of a number of established PMD compensation techniques is demonstrated experimentally using PMD compensators which we built and tested. Furthermore, investigations into the stability of PMD in deployed fibre networks under local conditions illustrate how PMD gradually drifts in buried fibre, and rapidly fluctuates in aerial fibre. These results confirm that PMD compensation is extremely difficult in aerial fibre due to the need to track the rapid PMD fluctuations continuously in real-time. We also briefly discuss possible alternative strategies besides PMD compensation for dealing with the PMD problem in the South African network. <![CDATA[<B>Stature estimation from bones of South African whites</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200010&lng=en&nrm=iso&tlng=en Stature reconstruction from skeletal remains forms part of the forensic anthropological analysis for the purpose of identification of the individual. The aim of this study was to derive regression formulae for the estimation of total skeletal height, and thereafter to predict stature in South African whites using long bone lengths. The sample comprised 98 white male and 71 white female skeletons from the Raymond A. Dart Collection of Human Skeletons and the Pretoria Bone Collection. For each individual, total skeletal heights and maximum long bone lengths were measured and used to produceunivariate regression formulae, with resulting correlations (r) ranging between 0.56 and 0.96. The lowest standard error of estimate (1.75 for females, 1.92 for males) was obtained when the lumbar spine, femur and tibia were used in combination, while the highest SEE (5.21 for females, 5.54 for males) was found when the lumbar spine was used on its own. Recently published corrections for soft tissue additions to obtain living height from total skeletal height make these kinds of formulae more usable, and will reduce the problem of underestimation. The derived formulae are population specific and are designed for use in forensic skeletal analyses of South African whites, but are also generally relevant to theoretical and practical issues in forensic anthropology. <![CDATA[<B>Simulating atmospheric turbulence using a phase-only spatial light modulator</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200011&lng=en&nrm=iso&tlng=en Demonstration of the effect of atmospheric turbulence on the propagation of laser beams is traditionally a difficult task. This is due to the complexities of long-distance measurements and the scarcity of suitable laser wavelengths in atmospheric transmission windows. We demonstrate the simulation of atmospheric turbulence in the laboratory using a phase-only spatial light modulator. We illustrate the advantages of this approach, as well as some of the limitations, when using spatial light modulators for this application. We show experimental results demonstrating these limitations, and discuss the impact they have on the simulation of various turbulence strengths. <![CDATA[<B>Interaction of Agulhas filaments with mesoscale turbulence</B>: <B>a case study</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200012&lng=en&nrm=iso&tlng=en The inter-ocean leakage of heat and salt from the South Indian Ocean to the South Atlantic has important consequences for the global thermohaline circulation and in particular for the strength of overturning of the Atlantic Ocean as a whole. This leakage between these two subtropical gyres takes place south of Africa. The main mechanisms are the intermittent shedding of Agulhas rings from the retroflection of the Agulhas Current and the advection of Agulhas filaments from the border of the Agulhas Current, both of which move northwestward into the South Atlantic. The subsequent behaviour and mixing of Agulhas rings has been much studied over the past years, that of Agulhas filaments not at all. We report here on fortuitous hydrographic observations of the behaviour of an Agulhas filament that interacted with a number of mesoscale features shortly after formation. This suggests that Agulhas filaments may be involved in many other circulation elements and not only the Benguela upwelling front, as was surmised previously, and may mix out in a very site-specific region. <![CDATA[<B>Beaked whale mysteries revealed by seafloor fossils trawled off South Africa</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200013&lng=en&nrm=iso&tlng=en An unexpectedly large number of well-preserved fossil ziphiid (beaked whale) skulls trawled from the seafloor off South Africa significantly increases our knowledge of this cetacean family. The eight new genera and ten new species more than double the known diversity of fossil beaked whales and represent more than one-third of this family (fossil and extant). A cladistic parsimony analysis based on 18 cranial characters suggested that some of these fossil taxa belong to the three extant ziphiid subfamilies, whereas others might represent extinct ziphiid lineages. Such high fossil ziphiid diversity might be linked to the upwelling system and the resulting high productivity of the Benguela Current, which has been in place and influenced conditions of the shallower waters along the southwest coast of South Africa and Namibia since the Middle Miocene. Both fossil and extant South African beaked whale faunas show a wide range in body size, which is probably related to different dietary niches and to wide exploration of the water column. Moreover, most South African fossil ziphiids share two morphological traits with extant species, which indicates that some of the behaviours associated with these traits had likely already developed during the Neogene: 1) the absence of functional maxillary teeth-providing clear evidence of suction feeding; and 2) the heavy ossification of the rostrum in specimens assumed to represent adult males-a feature which likely helps prevent injury and damage on impact during male-male fighting. <![CDATA[<b>A partial skull of <i>Paranthropus robustus</i> from Cooper's Cave, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200014&lng=en&nrm=iso&tlng=en A partial hominin skull (COB 101) was identified in the fossil collections of the Transvaal Museum, Pretoria, attributed to the Cooper's Cave site in South Africa. The find represents the most complete hominin specimen recovered from localities at this site to date. COB 101 comprises the supraorbital, zygomatic, infraorbital and nasoalveolar regions of the right side, and the right upper third premolar. The specimen has undergone post-depositional distortion that resulted in the flattening of the facial structures. Here we describe and compare COB 101 with other hominin material from Africa and find that this specimen shares numerous diagnostic features with Paranthropus robustus. The discovery of COB 101 augments the number of specimens attributed to this species from other South African sites and other Cooper's Cave localities. <![CDATA[<B>Characterization of a succession of small insect viruses in a wild South African population of <I>Nudaurelia cytherea capensis</I> (Lepidoptera: Saturniidae)</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200015&lng=en&nrm=iso&tlng=en The Tetraviridae are a family of small insect RNA viruses first discovered in South Africa some 40 years ago. They consist of one or two single-stranded (+) RNAs encapsidated in an icosahedral capsid of approximately 40 nm in diameter, with T = 4 symmetry. The type members of the two genera within this family, Nudaurelia β virus (NβV) and Nudaurelia ω virus (NωV), infect Nudaurelia cytherea capensis (pine emperor moth) larvae. The absence of N. capensis laboratory colonies and tissue culture cell lines susceptible to virus infection have limited research on the biology of NβV and NωV because the availability of infectious virus is dependent upon sporadic outbreaks in the wild N. capensis populations. In September 2002, dead and dying N. capensis larvae exhibiting symptoms similar to those reported previously in other tetravirus infections were observed in a wild population in a pine forest in the Western Cape province of South Africa. We report here the isolation of three small insect viruses from this population over a period of three years. Transmission electron microscopy and serological characterization indicate that all three are tetra-like virus isolates. One isolate was shown by cDNA sequence analysis to be NβV, which was thought to have been extinct since 1985. The two other isolates are likely new tetraviruses, designated Nudaurelia ψ virus (NψV) and Nudaurelia ζ virus (NζV), which are morphologically and serologically related to NωV and NβV, respectively. <![CDATA[<B>Isotopic evidence for contrasting diets of early hominins <I>Homo habilis</I> and <I>Australopithecus boisei</I> of Tanzania</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200016&lng=en&nrm=iso&tlng=en Isotopic dietary studies of early hominins have hitherto been confined to specimens from South Africa. We are now able to report isotopic analyses of two species of early hominins from Tanzania: Homo habilis and Australopithecus boisei. The results show that these two species had very different diets. The isotopic analyses of three South African species of early hominins, in contrast, show considerable variation in individual diets, but no marked differences between species. <![CDATA[<B>A comparison of drought stress and heat stress in the leaves and tubers of 12 potato cultivars</B>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532008000200017&lng=en&nrm=iso&tlng=en Potato yield is extremely sensitive to drought and heat stress, but there are variations in the degree to which cultivars are affected by these stresses. Strategies for the selection of stress-tolerant cultivars in a breeding programme can therefore be developed. The 2,3,5-triphenyltetrazolium chloride viability assay was evaluated to estimate drought and heat tolerance of leaves and tubers of 12 potato cultivars which differ in their response to drought. Floating leaf discs and tuber slices in 0.5 M mannitol (-1.24 MPa) simulated drought. After the drought acclimation treatment, the leaf discs were subjected to a lethal drought stress by exposure to an osmotic potential of -2.48 MPa. The viability of the leaf discs after the drought treatment was estimated spectrophotometrically by measuring the formazan concentration at 485 nm. Lower absorbance values in the control treatment, compared with the stress treatment, indicated a tolerant reaction. As drought simulation in the laboratory can differ from field conditions due to the effect of heat stress, the cultivars were also evaluated for heat tolerance. A stress index was established which can assist breeders to distinguish between plant responses to heat and drought.