Polyphenism

There are several types of polyphenism in animals, from having sex determined by the environment to the castes of honey bees and other social insects.

Sex-determining polyphenisms allow a species to benefit from sexual reproduction while permitting an unequal gender ratio.

[5] Population-dependent and reversible sex determination, found in animals such as the blue wrasse fish, have less potential for failure.

[5] While this system ensures that there will always be a mating couple when two animals of the same species are present, it could potentially decrease genetic variance in a population, for example if the females remain in a single male's territory.

In the case of the ant, P. morrisi, an embryo must develop under certain temperature and photoperiod conditions in order to become a reproductively-active queen.

Different pigmentation patterns provide appropriate camouflage throughout the seasons, as well as alter heat retention as temperatures change.

[5] Birds and mammals are capable of continued physiological changes in adulthood, and some display reversible seasonal polyphenisms, such as in the Arctic fox, which becomes all white in winter as snow camouflage.

[5] Predator-induced polyphenisms allow the species to develop in a more reproductively-successful way in a predator's absence, but to otherwise assume a more defensible morphology.

However, when the water level is low and desiccation is imminent, the tadpoles develop a morphology (wide mouth, strong jaw) that permits them to cannibalize.

In this species, cues of starvation and crowding by other nematodes, as sensed by pheromones, trigger a hormonal signal that ultimately activates a developmental switch gene that specifies formation of the predatory morph.

[9] Density-dependent polyphenism allows species to show a different phenotype based on the population density in which it was reared.

[11] This fits the model described above because a new mutation (black) was required to reveal pre-existing genetic variation and to permit selection.