Hormesis in ecotoxicological studies: A critical evolutionary perspective

Many studies report negative associations between exposure to large concentrations of contaminants and life-history traits of animals. As a consequence, they argue to derive linear models that can be applied to predict effects in sub-threshold or lowdose exposure scenarios. However, several recent studies found that exposure to low doses of a contaminant may induce a hormetic response, i.e. stimulatory or beneficial effects at low concentrations, but harmful effects at higher concentrations. Hormesis might be a novel fundamental pillar in the field of ecotoxicology, as it may promote the evolution of adaptive coping mechanisms in rapidly changing and challenging environments. However, because hormesis occurs in the lowdose zone of the dose-response, it has been often neglected. In this review, we have discussed how low-dose contaminant exposure may adaptively modify molecular and physiological mechanisms that may lead to organisms better capable of coping with challenging environments, how such responses may be transgenerational, and how thus this issue can no longer be ignored in ecotoxicological studies. In so doing, we have also identified some of the main limitations of ecotoxicological studies that, by masking potential hormetic responses of animals to chemicals, make the integration of hormesis complicated to achieve.