ABSTRACT
Polyphenism, broadly defi ned, is where two or more distinct phenotypes can be produced by the same genotype. Woltereck (1909) coined the term ‘reaction norm’ (Reaktionsnorm) to describe how the phenotype of an individual depends on the interaction between its particular genotype and environmental cues. In practice many or most genes with pleiotropic effects have context-dependent expression or action during development, i.e., the internal environment in which they are expressed. Phenotypic plasticity is therefore usually defi ned as a change in phenotype driven by cues in the external environment, which may be abiotic, such as temperature or photoperiod, or biological in origin, deriving from other species or even members of the same species. Phenotypic plasticity can result from variation in developmental, physiological, biochemical and behavioral processes that are sensitive to these environmental variables (Nijhout and Davidowitz 2009).
