Synergistic influence of temperature and 6PPD-Q on the development of Arctic Charr larvae: Differential effects between populations from Lakes Geneva and Annecy.

Freshwater ecosystems are experiencing significant biodiversity loss due to multiple anthropogenic stressors, including temperature fluctuations and chemical pollutants such as 6PPD-quinone (6PPD-Q), a toxic byproduct of tire wear. 6PPD-Q is known for its lethal effects on species like coho salmon (Oncorhynchus kisutch) and could pose considerable risks even at environmentally relevant concentrations. However, little is known about how 6PPD-Q interacts with warming to affect cold-water fish, especially during sensitive early life stages. Arctic charr (Salvelinus alpinus), a species endemic to alpine lakes, may be particularly vulnerable. Arctic charr larvae from Lakes Geneva and Annecy were exposed to two temperatures (5 °C and 8.5 °C) and either a water control (WW), a solvent control (<0.1% ethanol, WS), or 6PPD-Q at 1.5 or 3.0 µg/L. We assessed physiological, morphological, and behavioral traits to understand potential synergistic effects on development, survival, malformations, oxidative stress, and behavior. Results showed significant interactions, with warming intensifying the negative effects of 6PPD-Q. The chorion provided partial protection during embryonic development. Exposure to 6PPD-Q induced behavioral changes and elevated oxidative stress, likely through metabolic and cardio-respiratory disturbances. These findings emphasize the ecological risks of combined thermal and chemical stressors and the need to consider population-specific responses in environmental risk assessments.