Environment-specific heritabilities and maternal effects for body size, morphology and survival in juvenile Atlantic salmon (Salmo salar): evidence from a field experiment

Abstract

Environmental heterogeneity may strongly influence the amount of heritable variation in phenotypic traits and thus affect evolutionary responses to natural selection. However, the question of whether heritabilities change across environmental gradients has received little empirical attention, particularly for wild vertebrates. We tested whether levels of heritable variation in body size, morphology and survival of juvenile Atlantic salmon (Salmo salar) differed between water flow regimes. We exposed individuals of known genetic relationships to rearing habitats characterized by slow and rapid water flows in a field experiment. We found that the additive genetic variation in body size tended to be higher for individuals reared under rapid water flows. By contrast, the heritabilities of other morphological traits were not consistently higher in either water flow. We also found that salmon grew faster under rapid water flows but also suffered high mortality rates with little heritable variation explaining the variation in survival. However, part of the variation in survival in the rapid water flow was explained by maternal effects. Our results suggest a strong tendency for heritable variation, particularly in body size to be revealed only under specific environmental conditions, such as those that allow for rapid growth. We provide support for the hypothesis that genotype by environment interactions have important effects on the adaptive potential of phenotypes in nature.