Age-dependent genetic architecture underlines similar heritability of body size in sticklebacks

Heritable variation in traits under natural selection is a prerequisite for evolutionary response. While it is recognised that trait heritability may vary spatially and temporally depending under which environmental conditions traits are expressed, less is known about the possibility that genetic variance contributing to the expected selection response in a given trait may vary at different stages of ontogeny. Specifically, whether different loci underlie the expression of a trait throughout development - thus providing an additional source of variation for selection to act on - is unclear. Here we show that the heritability (h2) of body size, an important life history trait, remains constant across ontogeny in a stickleback fish. Nevertheless, both analyses of quantitative trait loci (QTL) and genetic correlations across ages show that different chromosomes/loci contribute to this heritability in different ontogenic time-points. This suggests that body size can respond to selection at different stages of ontogeny but that this response is determined by different loci at different points of development. Hence, this illustrates the notion that diverse genetic architectures may underline similar (expected) phenotypic outcomes, and that similar selection pressures may lead to genetically heterogeneous responses depending on what life stage selection is acting on.