Practice question

An ecad is a phenotypic form produced by environmental conditions within the plastic response of a genotype. Genetically similar plants, for example, may develop different leaf thickness, stature, or branching in sun, shade, wet, or dry habitats. These changes need not involve allele-frequency divergence and may disappear when individuals are transferred to a common environment. This is phenotypic plasticity: one genotype generates different phenotypes across environments, represented by its reaction norm. An ecotype differs because local traits are genetically based and remain heritable in a common garden, usually after natural selection has differentiated populations. An ecospecies is an evolutionary grouping of compatible ecotypes, while an ecotone is a transition between communities. Common-garden and reciprocal-transplant experiments distinguish plastic ecads from inherited ecotypes. Plasticity itself can be an evolved adaptation because selection can favour genotypes capable of producing suitable forms under variable conditions, but the particular induced morphology is not automatically a new genetic variety. The ecad concept therefore prevents environmental modification from being mistaken for permanent evolutionary divergence based solely on outward appearance.