The impact of non-native rainbow trout within Afro-montane streams in eastern Zimbabwe

Non-native trout species have been associated with many negative effects in receiving ecosystems. The first aim of this study was to determine the impact of non-native rainbow trout Oncorhynchus mykiss on distribution and abundance of native mountain catfish Amphilius uranoscopus within Afro-montane streams in Nyanga Mountains, eastern Zimbabwe. The second aim was to compare macro-invertebrate community responses to the presence of the trout and the catfish. We examined trout impact on catfish’s habitat associations, whereas macro-invertebrate composition was compared using open fish and fish exclosure experiments in habitats with and without trout. Trout influenced both the distribution and abundance of the catfish that occupied shallow reaches possibly to avoid predation from trout that occurred in the deeper habitats. Within trout invaded reaches, most macro-invertebrate taxa were more abundant in exclosure than open treatments. By contrast, within trout-free reaches, most macro-invertebrates either did not differ between treatments or were generally more abundant in open than exclosure treatments. This suggests that the macro-invertebrate communities responded differently within invaded and non-invaded reaches. By influencing distribution and abundance of native biota, non-native rainbow trout may have wider ecological effects, such as influencing trophic interrelationships within invaded habitats.     

The soil and plant determinants of community structures of the dominant actinobacteria in Marion Island terrestrial habitats, Sub-Antarctica

Marion Island is a Sub-Antarctic island made up of distinct ecological habitats based on soil physiochemical, plant cover and physical characteristics. The microbial diversity and ecological determinants in this harsh Sub-Antarctic environment are largely uncharacterized. Actinobacteria have diverse ecological functions related to soil and plant functioning. This study was aimed at characterizing the diversity and community structures of the dominant actinobacteria in the distinct habitats and to identify their determinant soil and plant characteristics. Using the 16S rRNA gene, the denaturing gradient gel electrophoresis patterns and clone library diversity were correlated with the soil and plant characteristics. Multivariate statistical methods were also used to identify determinant soil and plant characteristics. Salinity and pH were the most important soil determinants, and a number of important site-specific plant species may have been important. The Coastal Fellfield Habitat was dominated by sequences of the suborders Micrococcineae (44%) and Propionibacterineae (18%), with salinity identified as the principal determinant. The Cotula Herbfield Habitat was dominated by Frankineae (37%) and Streptosporangineae (38%), which were correlated with organic nutrient concentrations. The Wet Mire Habitat was dominated by Acidimicrobineae (61%), with moisture and organic carbon content as principal components. Culture-dependent studies were complementary to culture-independent studies with the majority of actinobacteria isolated not identified in 16S rRNA gene clone libraries. This study demonstrates how the soil physiochemical characteristics and plant species independently determine the community structures of the dominant actinobacteria in distinct ecological habitats. These factors subsequently influence their ecological adaptation, roles and functions.     

Novel inner membrane retention signals in Pseudomonas aeruginosa lipoproteins

The ultimate membrane localization and function of most of the 185 predicted Pseudomonas aeruginosa PAO1 lipoproteins remain unknown. We constructed a fluorescent lipoprotein, CSFP^OmlA-ChFP, by fusing the signal peptide and the first four amino acids of the P. aeruginosa outer membrane lipoprotein OmlA to the monomeric red fluorescent protein mCherry (ChFP). When cells were plasmolyzed with 0.5 M NaCl, the inner membrane separated from the outer membrane and formed plasmolysis bays. This permits the direct observation of fluorescence in either the outer or inner membrane. CSFP^OmlA-ChFP was shown to localize in the outer membrane by fluorescence microscopy and immunoblotting analysis of inner and outer membrane fractions. The site-directed substitution of the amino acids at positions +2, +3, and +4 in CSFP^OmlA-ChFP was performed to test the effects on lipoprotein localization of a series of amino acid sequences selected from a panel of predicted lipoproteins. We confirmed Asp⁺² and Lys⁺³ Ser⁺⁴ function as inner membrane retention signals and identified four novel inner membrane retention signals: CK⁺² V⁺³ E⁺⁴, CG⁺² G⁺³ G⁺⁴, CG⁺² D⁺³ D⁺⁴, and CQ⁺² G⁺³ S⁺⁴. These inner membrane retention signals are found in 5% of the 185 predicted P. aeruginosa lipoproteins. Full-length chimeras of predicted lipoproteins PA4370 and PA3262 fused to mCherry were shown to reside in the inner membrane and showed a nonuniform or patchy distribution in the membrane. The optical sectioning of cells producing PA4370^CGDD-ChFP and PA3262^CDSQ-ChFP by confocal microscopy improved the resolution and indicated a helix-like localization pattern in the inner membrane. The method described here permits the in situ visualization of lipoprotein localization and should work equally well for other membrane-associated proteins.     

Male terminalia variation in the rainforest dwelling <Emphasis Type="Italic">Drosophila teissieri</Emphasis> contrasts with the sperm pattern and species stability

It is commonly recognized that speciation does not necessarily imply extensive variation between populations, and what the speciation process per se consists of still remains an unanswered question. We advocate here that the variation of male terminalia does not necessarily result in noticeable reproductive isolation. We report whether there is invariance or variance of traits central to sexual selection processes (i.e. male terminalia and sperm length) compared to traits which are generally assumed to vary more neutrally (i.e. allozymes) in the strictly Afrotropical forest-dwelling continental species Drosophila teissieri. Three geographic blocks can be recognized along the present range of the species. Our data suggest that the components of the species integrity do not obey the variance/invariance alternative consistently. Male terminalia and allozymes show extensive variation while sperm length distribution is strikingly similar between the geographic blocks. It is therefore inferred that sperm length might be one of the major targets of stabilizing selection. Finally, it is suggested that the striking fit between the extent of sperm heteromorphism (within male) and sperm polymorphism (between males) is instrumental in maintaining the species integrity.     

Physico-chemical limnology and plankton dynamics of Mazvikadei,a tropical reservoir in Zimbabwe

The limnology of Mazvikadei Reservoir, northern Zimbabwe, was investigated in 2015 to determine whether it had changed since filling in 1990. The reservoir is characterised by low algal biomass, low nutrients (i.e. N and P) and high water clarity/transparency. Fifty-four species of phytoplankton were recorded, comprising Bacillariophyta, Chlorophyta, Cyanophyta, Desmids, Dinophyta and Euglenophyta. Chlorophyta numerically dominated in the hot dry season, whereas Bacillariophyta, Desmids, Dinophyta and Euglenophyta dominated in the cool dry season. Species richness was highest at the onset of the cool dry season, in response to high nutrient concentrations. Phytoplankton abundance and composition were significantly correlated with temperature, nitrates and total nitrogen. Nineteen zooplankton species were recorded, including Copepoda, Cladocera and Rotifera. Overall, Cladocera were numerically dominant and became most abundant during the cool dry season. Rotifers and copepods dominated during the hot dry season. The zooplankton abundance was correlated with reactive phosphorus and phytoplankton abundance. The trophic state of Mazvikadei Reservoir seems to have stabilised and to have assumed the physico-chemical characteristics and plankton community typical of an oligotrophic lake.     

Super‐beacons: Open‐source probes with spontaneous tuneable blinking compatible with live‐cell super‐resolution microscopy

Localization‐based super‐resolution microscopy relies on the detection of individual molecules cycling between fluorescent and non‐fluorescent states. These transitions are commonly regulated by high‐intensity illumination, imposing constrains to imaging hardware and producing sample photodamage. Here, we propose single‐molecule self‐quenching as a mechanism to generate spontaneous photoswitching. To demonstrate this principle, we developed a new class of DNA‐based open‐source super‐resolution probes named super‐beacons, with photoswitching kinetics that can be tuned structurally, thermally and chemically. The potential of these probes for live‐cell compatible super‐resolution microscopy without high‐illumination or toxic imaging buffers is revealed by imaging interferon inducible transmembrane proteins (IFITMs) at sub‐100 nm resolutions.     

An investigation into a possible relationship between vitamin D, parathyroid hormone, calcium and magnesium in a normally pigmented and an albino rural black population in the Northern Province of South Africa

Vitamin D levels are important in the management of patients with various disorders of calcium metabolism associated with rickets, osteomalacia, osteodystrophy osteoporosis and hypoparathyroidism. 82 albinos and 58 normally pigmented children resident at the Siloe School for the Visually Impaired were sampled. Blood samples of fasting subjects were collected over a two-day period and analyzed for vitamin D, parathyroid hormone, plasma calcium and both plasma and red blood cell magnesium measurements. The height and weight of each subject was also recorded. The results are discussed in relation to the different skin pigmented groups, for specific age groups, sex and visual status. Statistical outliers were excluded from the results. It appears that the Albino group has significantly (p = 0.06) higher vitamin D levels against the background of a similar dietary intake and similar exposure to sunlight/day length. Thus black children/subjects require a significantly higher intake of vitamin D to attain the same level as their Albino counterparts. In spite of significantly higher vit D levels, the other homeostatic control mechanisms were not altered (i.e., PTH levels are similar in both groups). This study supports the postulate that a dark complexion predisposes to sub-optimal vit D status.