Abstract
Electrophoretic analyses of population genetic structure, both in the laboratory and in the field, have documented significant shifts in allozyme genotype frequencies in a variety of aquatic taxa as a result of environmental impacts. Studies are documented which indicate that contaminants may select for individuals with tolerant allozyme genotypes, causing the potential loss of individuals with sensitive genotypes. This may diminish the genetic variability and fitness of affected populations and make them more susceptible to extinction following a subsequent stress. Future research involving population genetic structure and ecotoxicology should focus on determining the mechanism of sensitivity, documenting multigenerational effects of chronic laboratory exposure on population genetic composition, investigating whether previously stressed and genetically impacted populations are more susceptible to further natural and/or anthropogenic stressors, and establishing the utility of population genetic structure as a sensitive monitor of impacts in aquatic systems and their subsequent remediation.