The occurrence within a species of distinct morphological types (morphs) in response to environmental cues. The morphs, which may overlap in space and/or time, are the result of particular signals in the animals’ environment, such as nutrition, temperature, or day length, that interact with the animals’ genes and ‘switch’ development of the young from one ‘program’ to another. The resultant morphs are better adapted to their environmental conditions or to fulfil a certain role in a social group. For example, the southern African butterfly Bicyclus anynana exhibits two distinct morphs: a wet season morph, with prominent eyespots on its hind wings; and a dry season morph that is brown with much reduced eyespots. Ambient temperature and levels of ecdysteroid hormones in the pupa determine which morph will emerge. Polyphenism occurring in successive generations exposed to seasonal changes in the environment is termed cyclomorphosis. Compare polymorphism.