Delimitation of morphologically similar sponge crab species of the genus Pseudodromia (Crustacea, Decapoda, Dromiidae) from South Africa

Stewart, B. A., Gouws, G., Daniels, S. R. & Matthee, C. A. (2004). Delimitation of morphologically similar sponge crab species of the genus Pseudodromia (Crustacea, Decapoda, Dromiidae) from South Africa. — Zoologica Scripta , 33 , 45–55.
Presently, three Pseudodromia sponge crab species are recognized, all of which are endemic to the continental shelf off the coast of South Africa. Two of these differ only in the morphology of their rostral teeth, making them difficult to distinguish, and can thus be considered as cryptic species. In addition they have very similar distribution ranges, thus raising doubts as to their specific status. Discriminant function analysis of morphometric data, differentiation at 10 allozyme loci, and sequence data derived from the 12S rRNA mitochondrial gene were used to test whether specimens identified as P. latens and P. rotunda are morphological forms of a single, widespread species, or represent two, distinct, reproductively isolated species, and to establish whether these two taxa are sister species, and thus form a monophyletic entity. The presence of fixed allele differences at three, and strong genetic heterogeneity at five other allozyme loci, indicating no gene flow occurring between sympatric populations, as well as the relatively high degree of 12S rRNA and allozyme genetic differentiation observed, supported the recognition of P. latens and P. rotunda as separate species. The 12S rRNA topology suggested that the genus Pseudodromia , as presently constituted, is paraphyletic, thus inferring that the morphological characters used to define this taxon might not be useful for phylogenetic inferences. It was concluded that in view of the uncertainties raised regarding the designation and composition of certain genera within the family Dromiidae, further rigorous analyses of morphological and genetic data are needed to further our understanding of the taxonomy of the sponge crabs.     

Teratocarcinoma stem cells and early mouse embryos contain only a single major lamin polypeptide closely resembling lamin B

The nuclear lamina in adult mammalian somatic cells is composed of three major proteins, lamins A, B, and C. The expression of these proteins during the differentiation of teratocarcinomas and mouse embryogenesis is described. Embryos up to day 8 of gestation and embryonal carcinoma (EC) cells express only a single lamin species closely resembling, if not identical to, lamin B. Lamins A and/or C were detected in fertilized eggs, but disappear during the first 2-4 cleavage divisions, only reappearing in 8 day post-implantation embryos. These two lamins are absent from EC cells, but are strongly expressed in some of their derivatives. These results show that cells of the early mouse embryo do not have a functional requirement for lamins A and C and imply that the structural organization of the nucleus may change fundamentally during embryogenesis.     

Photoproduction of amino acids by mutant strains of N2-fixing cyanobacteria

Summary Mutant strains of the N₂-fixing cyanobacterium bacterium Anabaena variabilis resistant to 6-fluorotryptophan or to ethionine were isolated. Many of these strains liberated amino acids into their media in the absence of 6-fluorotryptophan and ethionine. Nitrogenase activity was higher in mutant strains than in the parent strain. Mutant strains were immobilised in calcium alginate and sustained photoproduction of amino acids has been demonstrated.Abbreviations ETH ethionine - FT 6-fluorotryptophan - Hepes 4-(2-hydroxyethyl)-1, piperazine ethanesulphonic acid - PEP phosphoenolpyruvate - DAHP 3-deoxy-d-arabinoheptulosonate 7-phosphate - chl a chlorophyll a     

A modular detector for flow cytometric multicolor fluorescence measurements

A modular detector for measuring multicolor fluorescence from cells illuminated by single or multiple lasers has been developed for flow cytometers. Motion picture projector, camera, and CCTV/video lenses were evaluated for use in the detector by comparing their physical characteristics, image quality, and light collection efficiencies. A 25-mm focal length F/0.95 CCTV lens was selected, based on our criteria and test results. The detector was constructed out of square aluminum extrusion channels. A CCTV lens mounted on the outside of the first channel collected light emitted from cells and collimated it towards filters and secondary CCTV lenses located in each channel. The secondary lenses functioned as relay optics for directing and focusing light onto pinhole spatial filters for measurement by photomultipliers. The detector design allowed any number of channels to be connected together and the versatility for making simultaneous or sequential measurements. Measurements on lymphocytes labeled with four monoclonal antibodies conjugated to fluorescent dyes and measurements on viable tumor cells stained for DNA content and with three fluorescent-labeled antibodies were used to demonstrate the detector's capabilities.     

Acid-mediated mutagenicity of tobacco snuff: its possible mechanism

Polar solvent extracts of tobacco snuff under acidic conditions were mutagenic in Salmonella typhimurium. Using the Griess reagent test, nitrite ranging from approximately 1.8 to 5.4 mg/g of snuff was found in the polar fraction of extracts. After acid treatment, nitroso compounds in the amount corresponding to the nitrite concentration were detected. The mutagenic potency of the acid-treated extracts was consistent with the content of nitroso compounds generated. Formation of nitroso compounds and the mutagenic activity under acidic conditions was inhibited by ascorbic acid. The results indicate that a nitrosation process was involved in snuff extracts during acid treatment. Studies related to the source of nitrite in tobacco snuff demonstrated that snuff contained bacteria which were able to reduce nitrate to nitrite and that the amount of nitrite in snuff extracts could be further increased by incubation of the extracts with the bacteria. Since snuff contains a considerable amount of nitrate, it seems that reduction of nitrate in snuff to nitrite by bacteria, and nitrosation of certain constituents in snuff by nitrite under acidic conditions to form mutagenic nitroso compounds are possible mechanisms responsible for the acid-mediated mutagenicity of snuff extracts.     

Gas exchange characteristics of the sorghum-striga host-parasite association

Gas exchange characteristics are reported for both members of the sorghum-Striga host-parasite association. Both Striga hermonthica (Del.) Benth and Striga asiatica (L.) Kuntze had transpiration rates considerably in excess of those of sorghum (Sorghum bicolor (L.) Moench, cv CSH1). Stomatal conductance in both Striga spp. showed little response to periods of darkness and moderate water stress. Low rates of net CO₂ fixation and high rates of dark respiration led to no net daily (24 hours) C gain, and Striga would appear to be reliant on its host for photosynthate. Infection of sorghum plants with either S. hermonthica or S. asiatica reduced host photosynthetic capacity. Infected sorghum plants were also more prone to water stress, but reduced rates of CO₂ fixation could not be accounted for in terms of lower stomatal conductance. Lower stomatal conductances were associated with an increase in water use efficiency (WUE) in uninfected sorghum; however, Striga-infected sorghum plants had lower WUE than those of uninfected plants. We suggest that Striga exerts a specific effect on processes affecting C acquisition in sorghum leaves. The water relations of S. hermonthica and S. asiatica are not characteristic of plants growing in semiarid environments and are more likely to reflect the nature of the parasitic life-style. Despite transfer of water and solutes from host to parasite, the reduction in C fixation observed in infected sorghum plants appears to be the major determinant of growth reductions observed in sorghum supporting Striga.     

Environmental factors influencing the vertical migration of planktonic rotifers in a hypereutrophic tarn

The diel vertical migration of planktonic rotifers in a small, hypereutrophic tarn was investigated on four occasions in 1983. When the tarn was isothermal the rotifers were distributed throughout the water column. After stratification, the rotifers were confined to the top 1–2 m of oxygenated water. On all four dates the rotifers were aggregated at specific depths in the water column. On some occasions, the pattern of aggregation changed as the animals performed distinct diurnal migrations. Keratella cochlearis, K. quadrata and Polyarthra vulgaris usually followed the reverse migrations of the phytoplankton. In contrast, the movements of Anuraeopsis fissa were less pronounced and were associated with variations in the depth of the oxycline.