The evolution of phenotypic polymorphism

Randomized strategies versus evolutionary branching

This new study, which will appear in the June 2005 issue of The American Naturalist, asserts that an individual could use his/her genotype as an informative cue when “deciding” which phenotype to develop. This is a new way of looking at certain kinds of genetic polymorphism. Some species have alternative phenotypes, which are different categories of adult individuals specialized for particular circumstances. For instance, if predation risk is high in some local environments and low in others, one category might have a predation resistant phenotype, with protective devices like spines, whereas the other category lacks these devices and is instead more efficient at producing offspring. If a developing individual can, statistically, predict the predation risk, it would be advantageous to develop the phenotype that fits the prediction. With spatial variation in predation risk, genetic determination of phenotypic alternatives can function as this kind of advantageous prediction, since natural selection will make genes for the protected type more common in local environments with high predation risk and less common in those with low risk.

Conceptually, this is the same as using some purely environmental cue signaling the presence of predators to infer the risk of predation. The evolutionary theory developed in this study suggests when genetic variation can function as an informative cue in this manner.