Phenotypic Plasticity

Phenotypic plasticity is the ability of one genotype to produce different phenotypes in response to different environments. The same set of genes can give rise to different shapes, behaviors or life histories, depending on conditions such as temperature, food or the presence of predators.

The water flea grows a helmet-shaped head and a spiny tail when it detects chemicals released by predators. Plant leaves grown in full sun are thicker and smaller than those grown in shade. Many insects develop different forms in different seasons, and the female larvae of the western honeybee become queens or workers depending on what they are fed. In some reptiles, the temperature of the nest decides the sex of the young.

Environmental cues alter gene expression during development, often through hormones and through chemical marks on DNA and histones that are part of epigenetics, such as DNA methylation. The relationship between an environment and the resulting trait is called a reaction norm, and its shape can itself differ between genotypes, which means plasticity can evolve.

Plasticity lets a population cope with change within one lifetime and can move organisms into new habitats, after which natural selection may fix the favored trait, a process called genetic assimilation or accommodation. It complicates the study of heritability, because part of the variation between individuals comes from their surroundings, and it matters for predicting how species will respond to climate change.