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The present study was conducted to assess three microevolutionary aspects of adaptation to pollution in Daphnia longispina populations historically exposed to an acid mine drainage from an abandoned pyrite mine: pollution mediated effects in acute tolerance to copper (Cu) and zinc (Zn); pollution-mediated effects on genetic variability of tolerant and physiological traits related to fitness (feeding rates); and fitness costs of tolerance measured as genetic trade-offs between tolerance and feeding rates under none and low levels of contamination. These objectives were addressed by comparing broad sense heritabilities and genetic correlations using up to 20 distinct clonal lineages randomly obtained from two populations: one located in a water reservoir contaminated by the acid mine drainage, and the other located in a nearby clean water reservoir. Results showed that only sensitive and resistant lineages to Cu were present in the reference and contaminated site, respectively. For Zn, however, both populations had a similar distribution pattern of sensitivities. Heritability values for tolerant and feeding traits across metal exposure levels was similar in both populations being in most cases greater than 50%. Fitness costs of tolerance were illustrated by lower feeding rates of the tolerant population compared to the reference one and negative genetic correlations between mean clonal feeding rates and median clonal survival time in control conditions (no added Cu or Zn). The results obtained thus support the view that tolerance to pollution is ecologically costly., ((c) 2009 SETAC.)

Studies investigating the use of biomarkers in pesticide risk assessment have greatly increased in recent years; however, issues concerning the ecological meaning of enzymatic responses have proved controversial. Ideally a good biomarker response should be modulated by the environmental contaminants alone and demonstrate a predictable behavior towards certain types of toxins. As these premises are rarely observed, the present study aims to outline research that has contributed to an understanding of the behavior of two widely used biomarkers, cholinesterase and glutathione-S-transferase, describing environmental and biotic factors that affect their response in freshwater invertebrates. Studies were performed in the main classes of aquatic invertebrates with these biomarkers and conclusions were reached concerning their behavior towards the main classes of pesticides. Links between biomarker responses and conventional endpoints were evaluated so that ecological relevance could be attributed to enzymatic responses. Toxicity of mixtures was investigated, and cases of synergism and antagonism were pointed out as factors changing the expected toxicity of aquatic systems and leading to misinterpretations of biomarker responses. Finally, the use of biomarkers as a tool for biomonitoring and in situ assays was investigated, with discussion of advantages and disadvantages of their use.