A new study in butterflies shows that similar developmental genetic mechanisms can be involved in both convergent and divergent evolution.

Homologous loci have been implicated in the evolution of convergent phenotypes, but can they also have a role in divergent evolution? To address this question, the authors studied the genetic architecture of colour pattern in three Heliconius butterfly species. Heliconius melpomene and Heliconius erato are distantly related and yet are phenotypically identical; Heliconius numata is a close relative of H. melpomene, but its wing patterns are divergent (and highly polymorphic).

Several Mendelian factors with large phenotypic effects control the pattern difference between races of H. melpomene and H. erato, whereas the mimicry polymorphism of H. numata is controlled by a single Mendelian locus, P, which behaves as a tight cluster or 'supergene'.

Using newly developed molecular markers that are tightly linked to a colour-pattern locus in H. melpomene, Joron et al. show that its N-Yb-Sb complex locus, which controls variation in yellow and white patterns, is homologous to the Cr locus in H. erato and the P locus in H. numata, and that local synteny is conserved. Given this conservation and the convergent and divergent phenotypes in these species, the data strongly argue “...against the idea that shared genetic architecture constrains morphological diversification”, implying that a single locus can underlie convergence and divergence.

How P might have gained control of the entire wing-pattern variability in H. numata awaits further investigations, which, given the available genomic resources, should not be far off.