Polyfenizm

Polyfenizm, also known as polyphenism, is a form of phenotypic plasticity in which a single genotype can produce two or more discrete phenotypes depending on environmental conditions. The alternative morphs arise through environmentally induced developmental pathways and are not fixed genetic variants; thus, polyfenizm differs from polymorphism, where genetic differences underlie the variation within a population.

Common environmental cues include population density, temperature, photoperiod, nutrition, and social context. The decision point often occurs during early development and leads to stable, irreversible morphological or behavioral phenotypes, although some systems allow later reversibility under certain conditions.

Classic examples include winged and wingless morphs in aphids triggered by crowding and host quality; caste differentiation in eusocial insects such as honeybees and termites, influenced by larval nutrition and hormonal signaling; seasonal morphs in butterflies (for example, Bicyclus anynana) that develop different camouflage or eye-spot patterns according to wet or dry seasons; and alternative mouth forms in nematodes such as Pristionchus pacificus, where diet cues determine predatory or microbial-feeding forms.

Mechanisms involve gene regulatory networks that translate environmental cues into hormonal signals (notably juvenile hormone and ecdysteroids in insects) and, in some lineages, epigenetic changes that lock in the developmental pathway. Polyfenizm can enhance fitness by producing specialized phenotypes suited to different conditions, though it may entail costs such as the need to defend multiple developmental strategies.

Polyfenizm is observed across major animal groups, especially insects and nematodes, and has become a focal point in studies of development, evolution, and ecology of plasticity.