Behavioral endpoints and generational effects in Daphnia magna upon short- and long-term exposure and their use as additional endpoint in ecotoxicological risk assessment

Daphnia magna is a common model organism for ecotoxicological testing. In regulatory guidelines, the classical tested endpoints are immobilization and reproduction. In order to detect other sublethal effects potentially more sensitive endpoints are required. Behavioral endpoints are one approach in environmental risk assessment for more sensitive endpoints and monitoring of water quality, demonstrating ecological relevance since altered behavior can impact reproduction and survival, yet they are rarely included in risk assessment. In literature, several chemicals have shown to alter swimming behavior of D. magna. The objective of our study was to identify suitable behavioral endpoints regarding sensitivity and applicability under short-term and long-term exposure to selected insecticides in environmentally relevant concentrations and potential generational effects of insecticide exposure. The investigated endpoints were locomotor activity, spatial orientation and predator avoidance behavior. Neonate D. magna were exposed to the insecticides imidacloprid, thiacloprid and fipronil for 48 hours during short-term exposure and for 14 days during long-term exposure. In a second step, for the investigation of generational effects, behavioral alterations of neonates born under insecticide exposure were tested. The investigated insecticides altered the swimming patterns of D. magna, with statistically significant effects observed at lower concentrations compared to the classical endpoints immobility and reproduction. Thus, the current study demonstrates that the assessment of behavioral endpoints helps in informing Mode of Action (MoA)-specific risk assessment.