Effect of Time of Temperature Exposure on Routine Metabolic Rate and Body Mass Scaling in Alpine Charr ( <i>Salvelinus umbla</i> )

The thermal dependence of metabolism has attracted much attention because metabolism is linked to many ecological properties, from individuals to ecosystems. The rate at which physiological traits change is an important factor to account for when assessing thermal plasticity since the time of exposure might allow organisms to compensate for the effect of temperature on performance. Here, we studied short- and long-term thermal plasticity of metabolic rate and its scaling with body mass of Alpine charr (<i>Salvelinus umbla</i>). To do so, we raised juveniles from Lake Geneva at 4.5°C and 8.5°C, measured their routine metabolic rate at their incubation temperature (long exposure, > 6 months), and individuals raised at 4.5°C were also tested at 8.5°C (short exposure, < 24 h). The metabolic rate of Alpine charr increased with temperature, as theoretically expected. We found no effects of duration of exposure on metabolic rate or its scaling with body mass. Despite a long-term exposure to higher temperature, individuals did not adjust their metabolic rate as compared to individuals exposed to a rapid increase in temperature, questioning the capacity of Alpine charr to compensate for temperature increase through their metabolic rate. Therefore, our data reveal no compensation mechanisms of Alpine charr to counterbalance the acute effect of temperature. Further studies will be required to fully understand the adaptive potential of Alpine charr in the context of global change.