Phenotypic plasticity explained
Light, temperature, nutrition, predators, water, and social conditions can alter development, physiology, morphology, or behavior without changing an individual's DNA sequence. A reaction norm describes the phenotype a genotype produces across environments. Genotypes can differ in those norms, providing variation on which evolution can act.
Scope: A worldwide introduction to environmentally responsive phenotypes across plants and animals. It distinguishes plasticity from genetic differences among populations and from evolution itself, while recognizing that reaction norms are genetically variable and can evolve. Plastic responses may be adaptive, neutral, costly, limited, or mismatched to novel conditions. · Last updated
One genotype can have a reaction norm
A reaction norm maps an environmental variable to the phenotype produced by a genotype. Plants may alter leaf form in air versus water, insects may develop different defenses with predator cues, and animals may shift physiology with temperature. These changes can be reversible or fixed during a developmental window. Demonstrating plasticity requires comparing the same genotype, clones, relatives, or controlled populations across environments. [1][2]
Plasticity is not genetic evolution within an individual
An organism responding to its environment does not rewrite population allele frequencies by doing so. Evolution occurs when heritable variation changes across generations. However, genotypes can differ in whether and how they respond, so selection can change reaction norms. Plasticity may also expose new phenotypic variation to selection, buffer genetic differences, or alter which environments organisms survive to experience. [1][3]
Responses carry information, costs, and limits
A useful plastic response depends on a cue reliably predicting future conditions and on the organism having time and resources to respond. Sensing, rebuilding tissues, or maintaining responsive machinery can be costly. If a novel environment breaks the cue–outcome relationship, a once-adaptive response may be too weak, too late, or pointed in the wrong direction. Plasticity therefore does not guarantee resilience to rapid climate change. [2][4]
Separate environmental and genetic explanations
Two populations that look different in the field may carry different genes, express plastic responses to different conditions, or both. Common-garden experiments raise them together; reciprocal transplants place each in both environments; pedigrees or genomic data add heritability evidence. Even these designs require care because maternal effects, early development, and epigenetic states can persist. A single photograph shows phenotype, not the cause of its variation. [3][4]
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Where this guide comes from
Source-checked editorial guide. Last updated . This guide teaches identification and field skills; it is not a substitute for expert verification when it matters.
- Philosophical transactions of the Royal Society of London. Series B, Biological sciences — Beyond buying time: the role of plasticity in phenotypic adaptation to rapid environmental change ↗
- Genetics — Phenotypic Plasticity: From Theory and Genetics to Current and Future Challenges ↗
- Heredity — Constraints on the evolution of phenotypic plasticity: limits and costs of phenotype and plasticity ↗
- Annals of botany — Characterization, costs, cues and future perspectives of phenotypic plasticity ↗
