Fig. 3.

Potential causes of phenotypic plasticity and genetic assimilation. (A) A new trait arises due to a change in gene regulation triggered by a novel environment. Two plausible mechanisms for genetic assimilation of the novel trait are illustrated: (B) evolution of the pathway underlying the novel trait such that it is no longer environmentally responsive; and (C) rewiring of development such that a new, environment-independent pathway causes the novel phenotype to be constitutively expressed. Note that genes 1, 2 and 3 represent genes that must be transcribed for the novel phenotype to be expressed, while signalling pathways 1 and 2 are pathways that can activate these genes. The thicker arrows in (C) indicate that signalling pathway 2 has a stronger effect on genes 1, 2 and 3 than signalling pathway 1.