Methods for distinguishing genetic and environmental variance in stress tolerance

Variations in stress response among separate populations of the same species have often been interpreted as local adaptations to different degrees of past exposure to specific stresses. However, it is possible that such interpopulation divergence may also be caused by developmental differences that are attributable to proximate environmental heterogeneity. In order to elucidate the origin and dynamics of stress tolerance, and to predict how individual populations may be affected by environmental changes or stress, it would be instructive to distinguish between genetic divergence and phenotypic variations. This paper, using examples of freshwater snails, examines two experimental procedures, namely, quantitative genetical and mass-culture techniques, available to separate genetic and environmental causes of interpopulation differences in stress responses, and discusses the potential complications in differentiating the above two hypotheses. Overall, a combination of controlled-breeding and mass-culture experiments will be necessary to provide the information required to differentiate genetically based and environmentally induced variations in ecologically relevant populations.