Quantitative genetics of lifetime growth curves in a lizard

While body size is an iconic trait in quantitative genetics, it bears little meaning without age information for species with indefinite growth. Instead, lifetime growth curves capture the same central aspect of individuals life-history, while accounting for its dynamics through time. Growth curve is a complex, function-valued traits, which requires a specialised framework to study its quantitative genetics. Here, we study growth in a squamate, the common lizard (Zootoca vivipara). We use two large datasets with available pedigree information: one from a wild population in a colder, montane environment; the other from an experimental population in a warmer, lowland environment. We found slower growth and larger asymptotic sizes in the colder population. We also found faster growth to lower asymptotic sizes for males. Inferences using a non-linear animal model show very low to moderate heritabilities in the parameters of individual growth curves, varying across populations and sexes. The decomposition of the additive genetic variance show a small to moderate heritability of the overall growth curves, with a stronger importance of the heritability in the shape of growth curves (variation in the dynamics of growth) than on their offset (variation between smaller and larger individuals). Genetic variation in growth curves differed between the two populations, with higher heritabilities in the experimental population. It also differed between sexes: there was more genetic variation in the growth rate at earlier ages for males, while genetic variation was larger for asymptotic size and at later ages for females. Our results tend to show that there is more adaptive potential in the earlier ages for males and in the later ages for females, which seems to be linked to their different life-history strategies. They also suggest that climate might have a positive impact on the adaptive potential of growth, which remains to be confirmed.