Social experience influences thermal sensitivity: lessons from an amphibious mangrove fish

Understanding factors affecting ectothermic fishes’ capacity to cope with warming temperature is critical given predicted climate change scenarios. We know that a fish’s social environment introduces plasticity in how it responds to high temperature. However, the magnitude of this plasticity and the mechanisms underlying socially-modulated thermal responses are unknown. Using the amphibious, selfing hermaphroditic mangrove rivulus fish ( Kryptolebias marmoratus ) as a model, we tested three hypotheses: 1) social stimulation affects physiological and behavioural thermal responses of isogenic lineages of fish, 2) social experience and acute social stimulation result in distinct physiological and behavioural responses, and 3) a desensitization of thermal receptors is responsible for socially modulated thermal responses. To test the first two hypotheses, we measured the temperature at which fish emerged (i.e., pejus temperature) with acute warming with socially naïve, isolated fish and socially experienced fish. Our results did not support our first hypothesis as fish socially-stimulated by mirrors during warming (i.e., acute social stimulation) emerged at similar temperatures as isolated fish. However, in support of our second hypothesis, prior social experience resulted in fish emerging at a higher temperature than socially naïve fish suggesting an increase in pejus temperature with social experience. We measured whole-body cortisol concentrations of socially naïve and socially experienced fish and determined that socially experienced fish had significantly higher cortisol concentrations than socially naïve fish. To test our third hypothesis, we exposed socially experienced and naïve fish to capsaicin, an agonist of TRPV1 thermal receptors. Socially experienced fish emerged at significantly higher capsaicin concentrations than socially naïve fish suggesting a desensitization of their TRPV1 thermal receptors. Collectively, our data indicate that past and present social experiences impact the behavioural response of fish to high temperature. We also provide novel data suggesting that social experience affects the capacity of fish to perceive warm temperature.