Phenotypic plasticity is the ability of a genotype to alter its phenotype in response to the environment. The classical quantitative genetics breeder's equation describes evolutionary responses of characters in a single environment. When we consider plastic characters, every element of that equation changes, from the genetic relationships among characters, phenotypic relationships among parents and offspring, patterns of correlated selection, and even the selective environment that organisms experience. Using examples from natural plant populations, I will illustrate how plasticity alters these important parameters. 105 Phenotypic plasticity is the ability of a genotype to alter its phenotype in response to environmental variation.
Phenotypic plasticity is hypothesized to be an adaptation to variable environments.
In order for plasticity to evolve in response to natural selection, genetic variation for plasticity must exist within natural populations. For plasticity to be adaptive, natural selection must favor the phenotype expressed in each environment relative to alternative phenotypes. I show that genetic variation for plasticity exists in natural populations and that natural selection favors plasticity under some conditions but not others. I also provide evidence for evolutionary responses to divergent selection on plasticity, and I discuss how plasticity that evolved in response to environmental variation within a site can influence performance in novel environments.