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 with fish that were raised alone and then given a short social experience prior to exposure to increasing temperature (i.e., 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, a short period of prior social experience resulted in fish emerging at a higher temperature than socially naïve fish suggesting an increase in pejus temperature with social experience. To test our third hypothesis, we exposed fish having had a brief social interaction 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 brief periods of social experience affects the capacity of fish to perceive warm temperature.