THERMOPREF

Environmental temperature plays a fundamental role in regulating biological processes in animals due to its influence on biochemical reactions. In particular, it strongly affects the metabolic performance of ectotherms by acting on enzyme activity and mitochondrial function. Mitochondria operate optimally within a specific thermal range (Topt), beyond which ATP production decreases because of increased proton leak and reduced coupling efficiency. Prolonged inefficiency can impair cellular function and lead to mortality associated with thermal stress. Temperature also influences organismal behavior, modifying thermal exposure and, in turn, physiological functions. Thus, before reaching the point of metabolic failure, ectotherms can mitigate thermal stress by moving to more favorable thermal environments. Such behaviors can be quantified by measuring thermal avoidance and tolerance in variable thermal conditions. The relationship between physiology and behavior is therefore crucial for understanding ectotherm movement in response to thermal changes, especially as heatwaves become more intense and frequent. However, the link between mitochondrial performance and behavioral thermal preference remains poorly established. In this context, this project aims to understand the impact of thermal acclimation on mitochondrial performance and on fish decision-making when choosing to remain in a warm environment or move to a cooler one. To establish this relationship between mitochondrial performance and individual thermal preference, we use juveniles of the European sea bass (Dicentrarchus labrax), a species inhabiting estuaries characterized by strong thermal variability. Using fish originating from the Aber Crozon and acclimated to either 15 °C or 20 °C for several months, we experimentally assess mitochondrial function in brain tissue and red muscle across a temperature gradient from 10 to 40 °C using high-resolution respirometry and ATP quantification. In parallel, we measure their thermal preference using a shuttle box system.