Extensive netting in Albasini and Nandoni dams: a potential threat to fish as a sustainable food source in the Vhembe District,South Africa

Fish populations in Albasini and Nandoni dams are negatively affected by extensive netting practices. This observation was made by the authors following a number of fish health assessment surveys related to aquatic pollution in the Luvuvhu River catchment. A comparison between the number and size of fish collected over a period of ten years indicated decreases in the average size and a consistent low number of fish, despite similar extensive sampling efforts. Unregulated netting is a common practice in both dams. This may become a serious problem as fish from these two dams are an important source of protein for the local communities. The purpose of this note is to report that gillnets are illegally used in the system and on the effect this could have on the fish population. The authors suggest educational and awareness initiatives to inform local communities about the importance of utilising fish in a sustainable manner to ensure the livelihood of generations to come.     

A molecular phylogeny of <Emphasis Type="Italic">Dorylus</Emphasis> army ants provides evidence for multiple evolutionary transitions in foraging niche

Background  

Army ants are the prime arthropod predators in tropical forests, with huge colonies and an evolutionary derived nomadic life style. Five of the six recognized subgenera of Old World Dorylus army ants forage in the soil, whereas some species of the sixth subgenus (Anomma) forage in the leaf-litter and some as conspicuous swarm raiders on the forest floor and in the lower vegetation (the infamous driver ants). Here we use a combination of nuclear and mitochondrial DNA sequences to reconstruct the phylogeny of the Dorylus s.l. army ants and to infer the evolutionary transitions in foraging niche and associated morphological adaptations.     

Chromatin structure of a P-element-transduced hsp-28 gene in Drosophila melanogaster.

The Drosophila hsp-28 gene was heat inducible when transduced to novel chromosomal sites even when no direct selection for transduced gene expression was imposed. The pattern of DNase I-hypersensitive sites 5' to the wild type and transduced copy of hsp-28 was similar. In addition, DNase I-hypersensitive sites occurred within the P-element sequences flanking transduced loci.     

Structural and dynamic states of actin in the erythrocyte

Analysis of the nucleotide tightly associated with isolated erythrocyte cytoskeletons show it to be ADP, rather then ATP. This confirms that at least a major part of the erythrocyte actin is in the F-form. A re-evaluation of the stoichiometry of spectrin and actin in the erythrocyte (taking account of a gross difference between the color responses of the two proteins on staining of electrophoretic gels) leads to values of 1x10(5) and 5x10(5) for the number of molecules of spectrin tetramer and actin respectively per cell. It has been found possible to perform spectrophotometric DNAase I assays fro actin on lysed whole cells. The concentration of monomeric actin at 0 degrees C is approximately 16 μg/ml packed cells. After washing the lysed cells the monomer pool is not re-established, indicating that only a small proportion of the actin subunits are free to dissociate. The actin monomer concentration in the cytosol remains unchanged after equilibration of the cells with cytochalasin E. The ability of actin-containing complexes in the membrane to nucleate the polymerization of added G-actin was measured fluorimetrically; it was found that membranes incubated with cytochalasin E were completely inert with respect to nucleating activity under conditions that favor appreciable growth at the slowly-growing (“pointed”) ends of free actin filaments. This suggests that these ends of the actin “protofilaments” in the red cell are blocked or sterically obstructed. After treatment of the membranes with guanidine hydrochloride under conditions that dissociate F-actin, the measured concentration of actin monomer rises to approximately 180 μg/ml of packed cells, which is nearly 70 percent of the total actin content. On treatment with trypsin in the presence of DNAase, the spectrin and 4.1 are extensively degraded, but the actin remains undamaged. This treatment, followed by exposure to guanidine hydrochloride, causes a further rise in the concentration of actin responsive to the DNAase assay to 250 μg/ml of cells, compared with 270 μg/ml estimated by densitometry of stained gels. The oligomeric complex, consisting of actin, spectrin, and 4.1, that is extracted from the membrane at low ionic strength, generates no detectable actin monomer after the same treatment. From literature data on the number of cytochalasin binding sites per cell and our value for the total actin content, we obtain a number-average degree of polymerization for actin in the membrane of 12-17. The results lead to a model for the structure of the cytoskeletal network and suggest some consequences of metabolic depletion.     

Current versus historical population sizes in vertebrate species with high gene flow: a comparison based on mitochondrial DNA lineages and inbreeding theory for neutral mutations

Using inbreeding theory as applied to neutral alleles inherited maternally, we generate expected probability distributions of times to identity by descent for random pairs of mitochondrial genotypes within a population or within an entire species characterized by high gene flow. For comparisons with these expectations, empirical distributions of times to most recent common ancestry were calculated (by conventional mtDNA clock calibrations) from mtDNA haplotype distances observed within each of three vertebrate species--American eels, hardhead catfish, and redwinged blackbirds. These species were chosen for analysis because census population size in each is currently large and because both genetic and life-history data are consistent with the postulate that historical gene flow within these species has been high. The observed molecular distances among mtDNA lineages were two to three orders of magnitude lower than predicted from census sizes of breeding females, suggesting that rate of mtDNA evolution is decelerated in these species and/or that long-term effective population size is vastly smaller than present-day population size. Several considerations point to the latter possibility as most likely. The genetic structure of any species is greatly influenced by historical demography; even for species that are currently abundant, mtDNA gene lineages appear to have been channeled through fairly small numbers of ancestors.      

Functional analysis of the chromo domain of HP1.

Heterochromatin protein 1 (HP1) is a non-histone chromosomal protein in Drosophila with dosage-dependent effects on heterochromatin-mediated gene silencing. An evolutionarily conserved amino acid sequence in the N-terminal half of HP1 (the 'chromo domain') shares > 60% sequence identity with a motif found in the Polycomb protein, a silencer of homeotic genes. We report here that point mutations in the HP1 chromo domain abolish the ability of HP1 to promote gene silencing. We show that the HP1 chromo domain, like the Polycomb chromo domain, has chromosome binding activity, but to distinct chromosomal sites. We constructed a chimeric HP1-Polycomb protein, consisting of the chromo domain of Polycomb in the context of HP1, and show that it binds to both heterochromatin and Polycomb binding sites in polytene chromosomes. In flies expressing chimeric HP1-Polycomb protein, endogenous HP1 is mislocalized to Polycomb binding sites, and endogenous polycomb is misdirected to the heterochromatic chromocenter, suggesting that both proteins are recruited to their distinct chromosomal binding sites through protein-protein contacts. Chimeric HP1-Polycomb protein expression in transgenic flies promotes heterochromatin-mediated gene silencing, supporting the view that the chromo domain homology reflects a common mechanistic basis for homeotic and heterochromatic silencing.