Hierarchical spatial organization and prioritization of wetlands: a conceptual model for wetland rehabilitation in South Africa

Wetland rehabilitation planning needs to take into account many different aspects of the wetland and its context. In South Africa, much emphasis is placed on the delivery of ecosystem services, poverty relief and skills development for those involved in labour-intensive rehabilitation measures. A framework is presented that facilitates decision-making with regards to wetland rehabilitation planning. This starts with prioritizing which wetlands need attention within a catchment. This is followed by decisions regarding which rehabilitation measures would be effective in improving certain ecosystem services based upon the aims of rehabilitation and the social context of the surrounding catchment. The functional unit that is most suitable to work with for rehabilitation is the Hydrogeomorphic (HGM) Unit, defined as a section of a wetland with more or less uniform hydrological and geomorphological characteristics. An individual wetland may comprise several HGM units, and a HGM Unit itself can be sub-divided into several smaller habitat or vegetation units. Different rehabilitation measures have been identified which are appropriate for the different scales in this spatial framework. Two case studies are presented as examples of how this spatial framework impacts upon the decisions made by the rehabilitation practitioner.     

Silencing of essential genes by RNA interference in Haemonchus contortus

In this study we assessed three technologies for silencing gene expression by RNA interference (RNAi) in the sheep parasitic nematode Haemonchus contortus. We chose as targets five genes that are essential in Caenorhabditis elegans (mitr-1, pat-12, vha-19, glf-1 and noah-1), orthologues of which are present and expressed in H. contortus, plus four genes previously tested by RNAi in H. contortus (ubiquitin, tubulin, paramyosin, tropomyosin). To introduce double-stranded RNA (dsRNA) into the nematodes we tested (1) feeding free-living stages of H. contortus with Escherichia coli that express dsRNA targetting the test genes; (2) electroporation of dsRNA into H. contortus eggs or larvae; and (3) soaking adult H. contortus in dsRNA. For each gene tested we observed reduced levels of mRNA in the treated nematodes, except for some electroporation conditions. We did not observe any phenotypic changes in the worms in the electroporation or dsRNA soaking experiments. The feeding method, however, elicited observable changes in the development and viability of larvae for five of the eight genes tested, including the 'essential' genes, Hc-pat-12, Hc-vha-19 and Hc-glf-1. We recommend the E. coli feeding method for RNAi in H. contortus and provide recommendations for future research directions for RNAi in this species.     

Two novel frameshift mutations in the low density lipoprotein receptor gene generated by endogenous sequence-directed mechanisms

DNA samples from 60 unrelated Belgian hypercholesterolemic patients were subjected to heteroduplex analysis of exon 4 of the low density lipoprotein receptor (LDLR) gene. Aberrant mobility bands were detected in 2 patients and the underlying mutations were characterized by DNA sequence analysis. Both mutations, a 19-bp insertion at codon 141 and a 23-bp deletion at codon 168, produce premature stop codons in the highly conserved ligand binding domain of the mature LDLR. Sequence data indicated that mispairing between short direct repeats during DNA replication is the most probable mechanism by which these mutations could have arisen. Our observations are consistent with an endogenous sequence-directed mechanism of mutagenesis.     

The role of geomorphology in evaluating remediation options for floodplain wetlands: the case of Ramsar-listed Seekoeivlei,eastern South Africa

The range of benefits bestowed by wetlands is today increasingly recognized, and remediation of degraded wetlands is being carried out around the world. Many degraded wetlands are associated with river floodplains, and an essential requirement for their remediation planning is a comprehensive knowledge of the geomorphological functioning of the river channel and floodplain. Here, we review previous geomorphological investigations of the Ramsar-listed Seekoeivlei floodplain wetlands, Free State Province, South Africa, and demonstrate how the knowledge gained is playing a key role in evaluating remediation options that are needed following more than a century of direct and indirect human impacts. Faunal and floral changes, coupled with channel modifications, have altered the flow and sediment regime and initiated major changes to erosional and depositional patterns, including promoting rapid headward growth of a new channel and abandonment of a former channel. These changes have led to further management interventions, including installation of weirs and erosion control structures. In an ideal world, remediation would strive to return a wetland to its natural, pre-impact state but, in reality, other management goals have to be taken into consideration. In the case of Seekoeivlei, these include maintaining current habitat and biodiversity (this has the added advantage of promoting local tourism, especially bird watching), and using the wetlands for water quality enhancement. Attempts to return the wetlands to their pre-impact state (e.g. by removing exotic trees and erosion control structures) would in fact further reduce habitat and biodiversity, permanently in the case of some avian species, and for centuries in the case of some aquatic species, because of the very slow natural rates of channel and floodplain change. Alternative options will all require ongoing intervention, albeit of variable intensity, but in effect will mean that the wetland will never return to its pre-impact state. Remediation will thus create an essentially ‘artificial’ wetland complex that restores some of the ecological and hydrological functions but that is likely to remain very far from its natural geomorphic condition.     

A double mutant LDL receptor allele in a Cypriot family with heterozygous familial hypercholesterolemia

Two novel mutations Q363X and D365E were identified in the low-density lipoprotein receptor gene in a Cypriot patient with heterozygous familial hypercholesterolemia. Restriction enzyme analysis of the index case and seven of her family members, by using AvaII and PvuII respectively, demonstrated that the two exon 8 mutations are transmitted in cis within the family. The disease phenotype is probably caused by the stop-363 mutation; this would result in a truncated protein that would probably be rapidly degraded in the extracellular space. Received: 15 August 1996 / Accepted: 10 February 1997     

LDLR Database (second edition): new additions to the database and the software, and results of the first molecular analysis.

Mutations in the LDL receptor gene (LDLR) cause familial hypercholesterolemia (FH), a common autosomal dominant disorder. The LDLR database is a computerized tool that has been developed to provide tools to analyse the numerous mutations that have been identified in the LDLR gene. The second version of the LDLR database contains 140 new entries and the software has been modified to accommodate four new routines. The analysis of the updated data (350 mutations) gives the following informations: (i) 63% of the mutations are missense, and only 20% occur in CpG dinucleotides; (ii) although the mutations are widely distributed throughout the gene, there is an excess of mutations in exons 4 and 9, and a deficit in exons 13 and 15; (iii) the analysis of the distribution of mutations located within the ligand-binding domain shows that 74% of the mutations in this domain affect a conserved amino-acid, and that they are mostly confined in the C-terminal region of the repeats. Conversely, the same analysis in the EGF-like domain shows that 64% of the mutations in this domain affect a non-conserved amino-acid, and, that they are mostly confined in the N-terminal half of the repeats. The database is now accessible on the World Wide Web at http://www.umd.necker.fr     

Inheritance of diflubenzuron resistance and monooxygenase activities in a laboratory-selected strain of Lucilia cuprina (Diptera: Calliphoridae).

Inheritance of the high-level diflubenzuron resistance shown by a laboratory-selected strain of Lucilia cuprina (Wiedemann) was examined in matings with a susceptible reference strain. Progeny of reciprocal crosses between resistant females and susceptible males showed higher LC50 values than the alternate reciprocal cross, indicating some maternal influence on inheritance of resistance. Resistance was inherited in a codominant (S male x R female) or incompletely recessive (R male x S female) manner. Monooxygenase activities (aldrin epoxidation) of the F1 generations were also intermediate between the levels shown by the parental lines, however, inheritance of enzyme activities showed greater degrees of dominance than for resistance levels. There was also some maternal influence on inheritance of monooxygenase activities. Backcrosses of F1 generations to both susceptible and resistant parents did not fit the expected patterns for a major sex-linked resistance locus, indicating that the maternal influence on resistance inheritance was not associated with sex-linkage of a major resistance gene. The backcross data also failed to fit the model for a single major autosomal gene, suggesting that the resistance in the diflubenzuron-selected strain is polygenic, involving mechanisms additional to monooxygenases.