To rise to temperature: Variation in temperature effects within and among populations

Temperature drives physiological changes on three timescales: acute, acclimatory and evolutionary. Acutely, passive temperature effects often dictate an expected two-fold increase in metabolic processes for every 10°C increase (Q10). Yet for acclimatory or evolutionary time scales, selection often mitigates these acute effects. This selection also should concomitantly reduce interindividual variation. However, the individual variation in physiological trait thermal sensitivity is not well characterized. Here we quantified physiological responses to a 16°C temperature difference across nine thermally distinct Fundulus heteroclitus populations. Traits included whole animal metabolism (WAM), critical thermal maximum (CTmax), and substrate-specific cardiac metabolism measured in approximately 350 individuals. These traits exhibit high variation among both individuals and populations that depends on acclimation temperature. Thermal sensitivity or Q10 variation is unexpected and ranges from 0...