Behavioral Disturbances: The Missing Link between Sub-Organismal and Supra-Organismal Responses to Stress? Prospects Based on Aquatic Research

Bridging the gap between early, sensitive responses to stress at the infra-organismal levels and long-term, ecologically relevant responses at the supra-organismal levels is a challenge. Behavioral ecotoxicology provides an approach that clearly links disturbances at the biochemical level (e.g., altered neurotransmitters and thyroid hormones) to effects at the population level. These effects may be direct, such as impairment of the search for a sexual partner, care of juveniles, and avoidance of predators or pollutants. Indirect effects may be alteration of reproduction success due to impairment of feeding and thus, energy metabolism. The sensitivity of behavioral responses can be useful in ecological risk assessment. A major difficulty is extrapolation of observed responses with test species to other species. Thus it is recommended to use behavioral biomarkers, associated with biochemical and physiological markers (neurotoxicity, hormones, energy metabolism) in carefully selected species. These sentinels must be key-species in the structure and functioning of ecosystems because impairments of their responses used as biomarkers will reveal a risk of cascading deleterious effects at the community and ecosystem levels.