Beyond conventional endpoints: behavioural and metabolic responses to chronic low-dose fluoxetine and copper exposure in Asellus aquaticus and implications for environmental risk assessment

Abstract Freshwater ecosystems are chronically exposed to low concentrations of pollutants that can alter organismal function without causing acute toxicity. Sublethal effects may appear as alterations in physiological or behavioural traits or in the relationships among traits. We investigated the effects of chronic low-dose exposure to copper and the selective serotonin reuptake inhibitor fluoxetine on the behaviour and metabolism of the freshwater isopod Asellus aquaticus. After 21 days of exposure to five chemical concentrations, including environmentally detected, for each chemical, we measured three behavioural traits (exploration, activity and escape behaviour) repeatedly across three days and metabolic rate once. We analysed toxicity effects on mean trait values, intra- and interindividual variability, and trait correlations (syndromes). Fluoxetine had no clear effect on any of the traits. In contrast, copper reduced mean exploration and activity. Strong correlations among behavioural traits in the absence of pollution disappeared at higher copper concentrations. No effect on variability was detected in any of the chemicals. These findings show that copper can destabilise behavioural expression and disrupt behavioural syndrome structure. Assessments of behavioural traits and trait correlations may provide a sensitive framework for detecting sublethal contaminant effects that may remain undetected by conventional endpoints.