Phenotypic Plasticity and Norms of Reaction: Synopsis
Phenotypic plasticity is the ability of a genotype to produce different phenotypes across an environmental gradient. Plasticity can be heuristically and graphically described as a univariate norm of reaction, a linear or non-linear function that expresses how the phenotypic value of a trait for a given genotype changes with the environment. Reaction norms describe how individuals respond to environmental change. Within an evolutionary context, norms of reaction pertain to responses by genotypes, the units of study when Woltereck (1909) first coined the term Reacktionsnorm in his work on Daphnia. Within the context of understanding how genotypes, and ultimately populations, might respond adaptively to environmental change, reaction norms provide information about the magnitude of trait plasticity and the presence of genotype × environment interactions on the phenotypic expression of a given trait. Thus, at the population level, reaction norms can be used to predict how individuals will respond, on average, to specific changes to an environmental variable. Genetic differences in reaction norms may reflect differences in the ability of populations to respond to environmental change. Reaction norms can also provide information on the extent to which the heritability of a trait changes with the environment, potentially providing insight into the rate at which the trait will respond to selection.