Regulatory networks may evolve to favor adaptive foresight

Abstract

Pleiotropy-a single mutation altering many traits-has long been seen as hindering adaptation. A new study in PLOS Biology offers a striking counterexample, suggesting that regulatory networks may evolve to ensure mutations are simultaneously beneficial in correlated environments.

Fig 1. Regulatory genes may be likely to show adaptive pleiotropy.

(A) Pleiotropic mutations have been typically associated with large deleterious side effects. Mutations in structural genes (Y and Z) should therefore be more likely to drive adaptation than mutations in regulatory ones (X). However, early adaptation in many evolution experiments with microbes is typically driven by large-effect, regulatory mutations. One explanation is that initial adaptation sometimes just requires altering the expression of a specific gene (Y), which can be more easily done through mutations in regulatory genes (X) than by other means. Another explanation is that, under conditions of global stress, mutations in regulatory genes may be the only feasible way to restore basic functionality across the many genes affected simultaneously (yellow, unlabeled circles). (B) A new article in PLOS Biology suggests a third explanation: regulatory networks may have evolved to generate mutations exhibiting “adaptive pleiotropy”—mutations that influence multiple traits at once in a way that is coherent under correlated selective pressures. In contrast to mutations in structural genes (Y and Z), mutations in an adaptively pleiotropic gene (X) will tend to have beneficial effects across conditions often encountered sequentially in the organism’s natural environment—giving the impression of adaptive foresight (note that in these landscapes, greater height corresponds to higher fitness). While intriguing, further experimental and theoretical work is needed to establish the generality of this phenomenon.