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Genetic variation within and among stone loach, Barbatula barbatula L., populations inhabiting anthropogenically degraded watercourses in Flanders (northern part of Belgium) was assessed using five microsatellite markers. High levels of genetic diversity were observed at all sampling sites, (MNA: 6.2–11.2; HO: 0.64–0.75; HE: 0.67–0.85). Estimates of the effective population size varied between 1535 and 3021 individuals and there were no indications of recent severe bottlenecks. Significant genetic differentiation was observed among sites belonging to different river systems and drainage basins. These results suggest human activities, such as pollution and river engineering, have not impacted significantly on genetic variability in the stone loach populations investigated. It is possible that this lack of genetic erosion may be attributed to species-specific characteristics such as pollution tolerance and ecological flexibility. [ABSTRACT FROM AUTHOR]

Anthropogenic disturbances cause the environment to change relatively fast. It is reasonable to assume that it is very unlikely for individuals to develop genetic adaptations to their polluted habitats, since adaptation through natural selection is a relatively slow process. Nevertheless, several studies have shown that such adaptations to changing environmental conditions may develop faster than anticipated. This study investigates the impact of historical metal pollution on a natural population of the gudgeon, Gobio gobio. Specimens from a contaminated site and a reference population were subjected to a series of three exposure experiments to cadmium after an acclimation period to reconstituted fresh water of 36 days. First, we performed an acute toxicity test on a sub-sample of both experimental groups to determine times-to-death (TTD) and lethal body burdens (LBB). The remaining individuals were used in a chronic Cd-exposure experiment, after which total Cd-body concentration, as well as Cd-concentrations and metallothionein-like protein (MTLP) levels in liver and gill tissue were determined. From the specimens that were not sacrificed for these measurements, a random subsample was subjected to a second acute toxicity test to evaluate the effect of chronic Cd-exposure (acclimation) on TTD and LBB. Our results show that, particularly after an extra acclimation period to a sublethal Cd-concentration, specimens originating from the contaminated sample area survived the acute exposure experiments better, despite the fact that neither the average Cd-accumulation rate, nor the lethal body concentrations differed between fishes from both groups. We also find that gudgeons from both populations translocated Cd from the gills (and probably also from other compartments) to the liver, where it can be more efficiently detoxified by MTLPs. Indeed, MTLP levels were found to increase faster in liver and gill tissue of specimens from the contaminated site, resulting in significantly higher MTLP-levels in the organs of these fishes. Although this study does not provide direct evidence for a genetic basis of Cd resistance (i.e. at the gene level), our results indicate that the regulation of MTLP-gene expression may involve a genetic component.

Although evidence of associations between genetic diversity and fitness in wild species has been published, the lack of a comprehensive review across species and the existence of contradictory results have led to scepticism remaining about its existence and importance in natural populations. In this study, the relationship between genetic diversity at six microsatellite loci and condition factor (a fitness related trait) was investigated at the population level in both Flemish and German populations of the European bullhead (Cottus gobio). A significant positive correlation was observed between genetic variability and the condition factor in Flemish but not in German bullhead populations. Environmental conditions such as conductivity of the water seemed more important in determining the condition factor of these latter populations. Regardless of the underlying mechanism(s) responsible for the different relationships, the results of this study suggest that both genetic and environmental variables can influence condition factor of bullhead populations.