How might evolving Heliconius jump from one adaptive peak to another without crossing fitness valleys below?
Single allele changes in regulatory genes (such as those controlling shutters and shutter color in the MCS clade) can create a strikingly novel pattern. Because major pattern themes are varied qualitatively by so few genes in this clade, hybridization of pattern genotypes having strikingly different phenotypes can produce qualitative variety among offspring resembling macro-mutation-like variants. Only a few such changes can instantly “beam” hybrids onto or near new peaks of mimetic protection without necessitating gradual evolution that puts between-peak variants at risk . Sheppard (1962), developed such ideas in reference to “major gene” mutation. Examples of the potential of the MCS tool box to promote colonization of new peaks of protection can be found in synthetic hybrid zones. In one example only two steps were required for hybridization of distinct cydno races to produce a near perfect mimic of a toxic moth (Figure 7 lower left) and in another, the F1 of a cydno X ismenius cros
