An assessment of the fish population of the lower reaches of the Sanyati River,Zimbabwe

The fish population of the lower reaches of the Sanyati River was studied using multifilament gillnets and monthly sampling was conducted over 13 consecutive months. A total of 15 fish species belonging to seven families were collected and variations in monthly catches and catch per unit effort and condition were observed. The five most common species exhibited a seasonal breeding pattern, with most breeding occurring in the rainy season. The exotic Nile tilapia Oreochromis niloticus was found to have established itself in the Sanyati River. The results of this study were compared with those of previous workers on Lake Kariba.     

Genetic variation in the liverwort Bazzania trilobata inferred from ISSR markers

Abstract

The distribution of Bazzania trilobata in Poland coincides with two parts of the natural distribution range of Norway spruce: the mountains of southern Poland and the northeastern lowlands. The occurrence of this species is connected with primeval forest communities and it was recognized as a relict of them. Genetic variation of 10 populations of B. trilobata from two different regions of Poland (lowlands and mountains) was studied in order to establish the genetic structure of this species and to compare the level of genetic variation within and among populations originating from primeval and managed forests. An analysis based on polymorphic inter-simple sequence repeat (ISSR) loci revealed a high level of total gene diversity in B. trilobata (H _T=0.308). A higher amount of polymorphism was found among than within populations. Genetic variation of populations from the primary forest (Tatras and Bia?owieza National Park) was higher than for those originating from disturbed habitats. The Bayesian method showed consistent grouping of samples corresponding with populations, with the best grouping in 12 different clusters reflecting a geographic pattern. The geographic pattern of genetic differentiation was supported by a neighbour-joining (NJ) dendrogram based on genetic distances. All mountain populations were grouped together in one subcluster, but lowland populations were more differentiated and did not form one clear group.     

Comparative analysis of pre-replication complex proteins in transformed and normal cells

This study examines the abundance of the major protein constituents of the pre-replication complex (pre-RC), both genome-wide and in association with specific replication origins, namely the lamin B2, c-myc, 20mer1, and 20mer2 origins. Several pre-RC protein components, namely ORC1-6, Cdc6, Cdt1, MCM4, MCM7, as well as additional replication proteins, such as Ku70/86, 14-3-3, Cdc45, and PCNA, were comparatively and quantitatively analyzed in both transformed and normal cells. The results show that these proteins are overexpressed and more abundantly bound to chromatin in the transformed compared to normal cells. Interestingly, the 20mer1, 20mer2, and c-myc origins exhibited a two- to threefold greater origin activity and a two- to threefold greater in vivo association of the pre-RC proteins with these origins in the transformed cells, whereas the origin associated with the housekeeping lamin B2 gene exhibited both similar levels of activity and in vivo association of these pre-RC proteins in both cell types. Overall, the results indicate that cellular transformation is associated with an overexpression and increased chromatin association of the pre-RC proteins. This study is significant, because it represents the most systematic comprehensive analysis done to date, using multiple replication proteins and different replication origins in both normal and transformed cell lines.     

Keeping the Home Fires Burning: The Changed Nature of Householding in the Kofyar Homeland

In the early 1960s, Robert Netting described households in the Kofyar homeland in Nigeria and explained their size, composition, and other characteristics as adjustments to agrarian ecology. Household changes attending movement to a frontier were analyzed in the same framework. By the 1980s, the economic rationale for homeland farming had all but disappeared, and some villages seemed on the verge of abandonment. Yet deliberate strategies for preserving homeland settlements had prevented abandonment. The demographic characteristics and household composition in the homeland now provide a window into a wholly different set of processes than what Netting described 30 years ago. Home settlement is kept viable as a facility to support ethnic identity and to attract government resources. Beneath superficial similarities are profound changes in the nature of the household and factors shaping it, reflecting the changed rationale for keeping the home fires burning.     

Population demographics of Palaemon peringueyi (Macpherson 1990) (Decapoda: Palaemonidae) in a small intermittently open Eastern Cape estuary

The population demographics of the caridean shrimp Palaemon peringueyi was investigated monthly at four sites over a period of one year in the small, intermittently-open Grants River Estuary situated on the south-east coastline of southern Africa. Mean total abundance and biomass of P. peringueyi ranged between 0 and 23.2 ind m^?2 and 0 and 2.3mg wwt m^?2, respectively. A peak in its abundance coincided with a breaching event that occurred in December 2004, and could be attributed to the mass recruitment of juveniles (carapace length <9mm) into the estuary. Minor peaks in abundance were also associated with marine waters overtopping the sandbar that separates the estuary from the marine environment. The highest biomass values were recorded when the estuary was separated from the sea. Maximum abundance and biomass values of P. peringueyi were generally recorded in the middle reaches of the estuary where extensive beds of submerged vegetation, mainly Potamogeton pectinatus, predominated. Pearson correlation analysis indicated that the total abundance of P. peringueyi was significantly correlated (r = 0.49; p < 0.05) to percentage cover of submerged vegetation. The spatial pattern in abundance and biomass values of the shrimp is thought to reflect the availability of refuge areas against predation. A distinct spatial pattern in the community structure of the shrimp was evident, with juveniles numerically dominating the samples in the lower reaches of the estuary, while mature females predominated in the upper reaches of the system. In the middle reaches, the community comprised both juveniles and adults.     

Book Review

Abstract

Most studies on population ecology of bryophytes have involved common species. However, some studies have compared life history strategies in rare and common species. We review the life history strategies (life expectancy, sexual and asexual reproduction, spore production, spore size and dispersal) for species that are rare in relation to pattern and persistency of suitable habitat patches. In particular, we discuss the dynamics on two levels, within and among localities, for different categories of rare species. We predict that most rare species will be found to have restricted dispersal capacities but higher than average life expectancies of local subpopulations. Natural rarity is distinguished from human-induced rarity and species rare for the latter reason are distinguished as 'threatened'.     

Catchments as conservation units for riverine biodiversity

The geological structure and longitudinal nature of river systems provide a possible barrier to the dispersal of lotic organisms. This has the potential to drive evolutionary processes such as genetic differentiation and subsequent allopatric speciation. In the conservation of lotic ecosystems population and evolutionary processes have largely been ignored. The traditional approach to river conservation has been focussed toward maintaining the physical habitat that provides the template for the biota. With a shift toward recognising the catchment as the primary operational unit for the conservation and management of lotic systems an examination of the biological relevance of these catchment units is required. This paper examines the structural influence of catchment units over population structure in lotic organisms and the extent to which catchments reflect populations and represent evolutionarily significant units. These being unique assemblages representing segments of biological diversity that share a common evolutionary lineage and contain the potential for a unique evolutionary future. This is of particular importance given the increased use of inter-basin water transfers to move water between historically isolated catchments and recognition of the catchment as the primary unit for the conservation and management of river ecosystems.     

Clonal distribution,fertility and sex ratios of the moss Plagiomnium affine (Bland.) T.Kop. in forests of contrasting age

Abstract

Six populations of the clonal forest floor moss Plagiomnium affine from forests of different age were screened for genetic variation at 23 allozyme loci, of which nine were polymorphic. Samples consisting of two adjacent unconnected shoots were taken at regular intervals along one transect from each population. A total of 602 shoots was analysed. Almost 80% of the shoots were sterile (i.e. not expressing male or female gender). Sex remained unknown for only 10% of shoots after identification of genets based on electrophoretic data. We identified a mean number of 3.7 fertile clones per population. The mean length of clones along transects in each population ranged between 2 and 3 m. The size distribution within populations was bimodal, with a few dominant clones and a varying number of much smaller clones. The overall sex ratio was slightly female biased at the ramet level, but balanced at the genet level. Forest age was negatively correlated with percentage of sterile shoots and positively correlated with frequency of sporophytes. In both cases correlations were significant only if population 1, which was subject to extreme soil disturbance by badgers, was excluded. We conclude that the effective population size is larger, and the susceptibility to genetic drift is lower, in old forests.