Fonti Kar, Shinichi Nakagawa, Christopher R Friesen, Daniel W.A. Noble

1. Physiological processes of individuals can be highly variable and there is mounting evidence that individuals can differ in how they respond to environmental change. The ability for individuals to reversibly adjust their metabolic rate in response to temperature (i.e., metabolic thermal plasticity) may affect mass-scaling at the population level. This process has rarely been investigated before.
2. This study characterised the repeatability of metabolic thermal plasticity and tested how mass-scaling exponents change at different temperatures in the delicate skink (Lampropholis delicata). We repeatedly measured standard metabolic rate of forty-two individuals at six temperatures over the course of three months (N[measurement] = 2418). We explicitly accounted for multi-level variation in our data in order to quantify more precise estimates of mass-scaling exponents at different environmental temperatures.
3. Making use of two analytical frameworks, we found that metabolic thermal plasticity was significantly repeatable. Average standard metabolic rate increased as a function of temperature, which was associated with individuals responding more predictably (a decrease in within-individual variance) at higher temperatures. Interpretation of repeatability estimates and cross-temperature correlations varied slightly between the analytic approaches, but they were mostly in agreement.
4. After taking into account within- and among-individual level variation in our data, our estimates for mass-scaling did not change with temperature and were in line with published values for snakes and lizards. This suggests that repeatable plastic responses may contribute to thermal stability of scaling exponents.
5. Our work contributes to our understanding of whether phenotypic plasticity has the capacity to respond to selection which is particularly important for animals coping with rapid environmental change. Acknowledging multi-level variation in body mass and metabolic rate is not only important for comparative studies interested in mass-scaling across the animal kingdom, but also to theoretical research interested using the predictive power of mass-scaling.