Serum IgG, IgA and IgM levels in rural Namibian infants.
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Age Factors↗
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Growing in silence: selected regions and countries with expanding HIV/AIDS epidemics.
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Acquired Immunodeficiency Syndrome↗
How brachiopods get covered with nanometric silicon chips.
The investigation of an early pelagic juvenile of the discinid brachiopod Discinisca cf. tenuis elucidates the so far enigmatic origin of nanometric silicon chips covering the brachiopod's juvenile shell. The siliceous tablets are products of an intracellular process within specialized cells of the animal's inner mantle epithelium. These specialized cells are arranged in a circumferential row and contain vesicles, which provide 'reaction chambers' osmotically separated from the cytoplasm. Up to 15 tablets per vesicle are released into the cell by vesicle burst, followed by a coordinated extrusion onto the periostracum. In conjunction with the conveyor belt mechanism of periostracum formation, the regime of tablet release accounts for the highly ordered arrangement of siliceous tablets in parts of the shell's surface. The siliceous tablets are discussed as a protective cover against solar radiation, inherited from Palaeozoic linguliform brachiopods.
Animal Structures↗
Genetic and behavioural evidence of monogamy in a mammal, Kirk's dik-dik (Madoqua kirkii).
Little is known about the mating behaviour of monogamous mammals. Here, we present behavioural and genetic evidence of fidelity in a socially monogamous dwarf antelope, Kirk's dik-dik. DNA microsatellite analysis revealed no evidence of extra-pair paternity (EPP) in dik-diks: mothers' partners matched the paternal genotype in all 12 juveniles tested. One likely reason for the absence of EPP is that males guard their mates closely during oestrus and over-mark all female scent, thereby reducing the likelihood of other males attempting to mate. In addition, males may be limited in their ability to search for extra-pair populations (EPCs) by activities associated with pair-bond maintenance. Year-round, males maintained proximity within pairs, followed their females' activity patterns, and spent approximately 64% of their time with their partners. However, males did attempt to obtain EPCs when the opportunity arose, and genetic monogamy in dik-diks is probably best explained by the behaviour of females: in contrast to many monogamous female birds, female dik-diks do not appear to seek EPC partners. We propose that females avoid extra-pair males because they are unable to mate with them without instigating a potentially dangerous conflict.
Animals↗
Footprints in the sand: independent reduction of subdigital lamellae in the Namib-Kalahari burrowing geckos.
Many desert organisms exhibit convergence, and certain physical factors such as windblown sands have generated remarkably similar ecomorphs across divergent lineages. The burrowing geckos Colopus, Chondrodactylus and Palmatogecko occupy dune ecosystems in the Namib and Kalahari deserts of southwest Africa. Considered closely related, they share several putative synapomorphies, including reduced subdigital pads (toe pads) and spinose digital scales. Though recognized as part of Africa's ecologically diverse Pachydactylus Group, the burrowing geckos' precise phylogenetic affinities remain elusive. Convergent pedal modification provides a tenable alternative explaining the geckos' derived terrestriality and adaptation to Namib and Kalahari sands. We generated a molecular phylogeny for the Pachydactylus Group to examine evolutionary relationships among the burrowing geckos and infer historical patterns of pedal character change. Bayesian and parsimony analyses revealed all three burrowing genera to be deeply nested within Pachydactylus, each genus belonging to a separate clade. Strong support for these distinct clades indicates ecomorphological adaptations for burrowing have evolved independently three times in the southern Pachydactylus Group. We argue that the physical properties of Namib and Kalahari sands played a principal role in selecting for pedal similarity.
Animals↗
Horse microsatellites and their amenability to comparative equid genetics.
We investigated the applicability of microsatellite primers, designed in horses, for use in plains and mountain zebras. Fifteen of the 20 tested horse-isolated primer pairs reliably amplified polymorphic loci in two wild equid species. We used this information to assess whether levels of genetic variation and repeat size differed in species from which microsatellites were isolated and in closely related target species. Target equid species exhibited similar levels of genetic variation to the horse, the species from which primers were originally isolated. We show that ascertainment bias results in lower mean and modal repeat size in target species. The data also provide evidence for a bi-directional mutational constraint in allele size across three equid species.
Alleles↗
Colony structure and parentage in wild colonies of co-operatively breeding Damaraland mole-rats suggest incest avoidance alone may not maintain reproductive skew.
Colonies of co-operatively breeding African mole-rats have traditionally been thought to be composed of a single breeding female, one or two breeding males, and their offspring. In the naked mole-rat (Heterocephalus glaber), the occurrence of facultative inbreeding means incest avoidance cannot prevent reproduction in subordinate group members, and physiological suppression of reproductive function by the breeding female occurs in both sexes. In contrast, previous studies of captive colonies of the Damaraland mole-rat (Cryptomys damarensis) suggest that breeding within a colony is restricted to a single breeding pair, simply because all other colony members are highly related (first- or second-order relatives) and this species is an obligate outbreeder. Using microsatellite markers, we investigated parentage and colony composition in 18 wild Damaraland mole-rat colonies to determine whether inbreeding avoidance alone can explain the high levels of reproductive skew in this species. Multiple and unidentified paternity was widespread within colonies and immigrants of both sexes were regularly identified. Unrelated, opposite-sex nonbreeders were found coexisting in two colonies. These results suggest that, in the wild, conditions exist where nonreproductive females can come into contact with unrelated males, even when they do not disperse from their natal colony. Inbreeding avoidance alone is therefore insufficient to maintain the high levels of reproductive skew identified in this species suggesting that the breeding female somehow suppresses the reproductive function in nonbreeding females.
Animals↗
HLA-DP polymorphism in the present-day San (Bushmen) and Khoi (Hottentots) using polymerase chain reaction and sequence-specific oligonucleotide typing.
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Amino Acid Sequence↗
C4 polymorphism and extended HLA haplotypes in Namibian San and Khoi and in South African Xhosa.
We studied C4A and C4B polymorphisms and HLA-B and -DR associations in the San, Khoi and Xhosa. C4A and C4B alleles were determined using conventional protein allotyping methods. The C4A*3, C4B*1 haplotype had a high frequency (30-55%) in all populations. The frequency of C4A*3, C4B*Q0 was 7-19%. The C4A*Q0, C4B*1 haplotype was frequent (15%) in the Khoi but very rare in the San (P < 0.001). C4A*12 A*91, C4B*Q0 was frequent in the Xhosa (15%) but rare in the San and Khoi (P < 0.001). Alleles C4A*5 and C4A*6, and the C4B*2 B*92 duplication were only found in the Xhosa. C4A alleles A*4, A*45, A*58, A*12, A*14, A*19 and the C4A*3 A*91 duplication were only found in the San/Khoi population group. In the San, fourteen extended haplotypes were found in a relatively high frequency (2-7%). In the Xhosa, one extended haplotype (B42, C4A*12 A*91, C4B*Q0, DR18) was found in a very high frequency (13%) and was characteristic for this group; five other extended haplotypes were found with a low frequency (< 3%).
Complement C4a↗
Recent trends in Namibian urbanization.
"The theoretical debates on urbanization and spatial inequalities in development are sketched in relation to the Namibian (South West African) situation. 1951, 1960 and 1970 Population Census data as well as 1976 estimates for urban centres are analysed and interpreted, revealing growth trends in the urban hierarchy and in the three main racial groups in each town."
Africa↗
A polydiagnostic approach to the differences in the symptoms of schizophrenia in different cultural and ethnic populations.
This study evaluates the pathoplastic influences of ethnicity and culture on the symptoms of schizophrenia. A sample of 113 schizophrenics was evaluated using the Present State Examination (PSE) and Landmark's Manual for the Assessment of Schizophrenia. The subjects were 57 coloured and 56 black individuals. Six different tribes of Bantu, Negroid and Khoisan origin and with different language and cultural backgrounds were represented among the black subjects. Core symptoms remained basically the same in two groups, but the content of positive symptoms was found to be influenced by culture. However, no statistically significant differences in the presentation of negative symptoms were found in terms of quantity, but there were qualitative differences between the ethnic groups.
Adolescent↗
An overview of networking for physicians and problems of network consulting in remote areas.
For computer networking the most suitable operating systems are UNIX or MS-DOS. As networking software UUCP and TCP/IP are most common. Hardware requirements are derived from the operating system and from the networking software. Low-cost solutions, for example, uuPC, a public domain version of UUCP, require only an 8088 processor and a 2400-baud modem. TCP/IP fares better with more powerful processors and requires permanent lines between the connecting computers. In developing countries the introduction of computer networks is hampered by several factors: lack of foreign exchange, price of hardware and software, unreliable electricity and telephone lines, lack of hardware and software support, large distances to the nearest center, and incompatibilities between existing systems and the network. Important aspects for clinical networking in developing countries include appointment scheduling in the referral hospitals, access to laboratory and pathology results from the central laboratory, and primary health care information such as epidemiologic data. Advanced systems, for example, for image processing, are not yet feasible in developing countries.
Computer Communication Networks↗
Laboratory evaluation of pathogenicity of entomogenous nematodes to African tick species.
Five strains of entomogenous nematodes, Steinernema carpocapsae strains DD, Mexican, SR, and Heterorhabditis bacteriophora strains 1S5 and HP88, were tested for their pathogenicity to various developmental stages of five African tick species namely; Rhipicephalus appendiculatus, R. evertsi, Amblyomma variegatum, A. gemma, and Boophilus decoloratus. In engorged female R. appendiculatus, all nematodes at a concentration of 1,000 infective juveniles (IJ)/dish, except S. carpocapsae Mexican strain, induced high mortalities (56-100%), whereas in engorged female R. evertsi, only S. carpocapsae DD and H. bacteriophora HP88 induced high mortalities (78% and 56%, respectively). In engorged B. decoloratus, S. carpocapsae DD, Mexican, SR and H. bacteriophora HP88 (100 IJ/dish) induced mortalities of 85%, 65%, 80%, and 100%, respectively. In all cases, except for S. carpocapsae Mexican strain, a higher concentration (5,000 IJ/dish) did not result in higher mortality than occurred with 1,000 IJ/dish. Unfed females and immature stages of ticks were found to be generally resistant to the nematodes. The feasibility of using entomogenous nematodes for biological control of African tick species are briefly discussed.
Africa↗
Laboratory and field evaluation of entomogenous fungi for tick control.
Aqueous and oil-based formulations of two entomogenous fungi, Beauveria bassiana and Metarhizium anisopliae were tested for their efficacy against the three major species of African ticks; namely, Amblyomma variegatum, Rhipicephalus apendiculatus, and Boophilus decoloratus. Both fungal species and formulations were observed to induce high mortalities, especially in the larvae. The oil-based formulation was found to be more effective than the aqueous formulation. Monthly application of aqueous formulations of B. bassiana and M. anisopliae on vegitation in paddocks significantly reduced numbers of the tick R. appendiculatus on cattle. Possibilities for using entomogenous fungi in tick control, alone, or in combination with the conventional acaricides are discussed.
Africa↗
A survey for antibodies to equine arteritis virus in donkeys, mules and zebra using virus neutralisation (VN) and enzyme linked immunosorbent assay (ELISA).
A seroepidemiological survey of donkeys in South Africa (n = 4300) indicated a wide distribution and increasing prevalence of antibodies to equine arteritis virus (EAV). Donkey sera inhibited equine arteritis virus infection in virus neutralisation (VN) tests and in ELISA specifically bound to a recombinant antigen derived from the Bucyrus isolate of EAV. These results suggest that donkeys have been exposed to the same serotype of this virus as circulates among horses. A good correlation existed between EAV neutralising antibody titres and ELISA absorbance values (0.8631); the ELISA was sensitive and specific (99.2% and 80.3% respectively) for donkey sera when compared to the VN test and the recombinant ELISA antigen did not cross-react with sera positive for common African equine pathogens. VN+ ELISA+ donkeys were also found in Morocco and Zimbabwe and seropositive mules in both South Africa and Morocco. No seropositive zebra (n = 266) were detected from game reserves or zoos in 9 countries. The results confirm that in addition to horses and donkeys, mules are naturally infected with EAV.
Animals↗
Giant sulfur-eating microbe found.
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Bacteria↗
Dense populations of a giant sulfur bacterium in Namibian shelf sediments.
A previously unknown giant sulfur bacterium is abundant in sediments underlying the oxygen minimum zone of the Benguela Current upwelling system. The bacterium has a spherical cell that exceeds by up to 100-fold the biovolume of the largest known prokaryotes. On the basis of 16S ribosomal DNA sequence data, these bacteria are closely related to the marine filamentous sulfur bacteria Thioploca, abundant in the upwelling area off Chile and Peru. Similar to Thioploca, the giant bacteria oxidize sulfide with nitrate that is accumulated to </=800 millimolar in a central vacuole.
Bacteria↗
Upwelling intensification as part of the Pliocene-Pleistocene climate transition.
A deep-sea sediment core underlying the Benguela upwelling system off southwest Africa provides a continuous time series of sea surface temperature (SST) for the past 4.5 million years. Our results indicate that temperatures in the region have declined by about 10 degrees C since 3.2 million years ago. Records of paleoproductivity suggest that this cooling was associated with an increase in wind-driven upwelling tied to a shift from relatively stable global warmth during the mid-Pliocene to the high-amplitude glacial-interglacial cycles of the late Quaternary. These observations imply that Atlantic Ocean surface water circulation was radically different during the mid-Pliocene.
Atlantic Ocean↗