Genetic and environmental effects on the scaling of metabolic rate with body size.

Metabolic rate (MR) often scales with body mass (BM) following a power function of the form MR=BM , where log() is the allometric intercept and is the allometric exponent (i.e. slope on a log-log scale). The variational properties of have been debated, but very few studies have tested for genetic variance in , and none have tested for a genotype-by-environment (G×E) interaction in Consequently, the short-term evolutionary potentials of both and its phenotypic plasticity remain unknown. Using 10 clones of a population of , we estimated the genetic variance in and assessed whether a G×E interaction affected We measured MR on juveniles of different sizes reared and measured at three temperatures (17, 22 and 28°C). Overall, decreased with increasing temperature. We found no evidence of genetic variance in at any temperature, and thus no G×E interaction in However, we found a significant G×E interaction in size-specific MR. Using simulations, we show how this G×E interaction can generate genetic variation in the ontogenetic allometric slope of animals experiencing directional changes in temperature during growth. This suggests that can evolve despite having limited genetic variation at constant temperatures.