Ontogenetic change in genetic variance in size depends on growth environment.

Within populations, the amount of environmental and genetic variation present may differ greatly among traits measured at multiple times over ontogeny. Brief periods of food deprivation are often followed by a period of accelerated (compensatory) growth. Early laboratory studies likewise reported a contraction of genetic variance in size as maturation approached. However, studies of wild populations often contradict these laboratory results. One possibility is that environmentally imposed stress is exposing genetic variance not seen in the laboratory. We tested the effect of rearing environment (high or low food) on genetic variance in size traits measured at two ages in the ladybird beetle Harmonia axyridis. A substantial amount of genetic variance was present in all combinations of rearing environment by ontogenetic stage among males. The pattern of change in male variance in mass over ontogeny was of opposite sign in the two food treatments, which may reflect cryptic genetic variance that is apparent only under stress. The proportion of overall variance that was due to additive genetic effects was much lower in females than in males, which suggests that the underlying genetics of female growth trajectories differs from that males. Our experimental design afforded an initial exploration of the genetics of compensatory growth.