Heliconius erato and H. melpomene have evolved over 20 distinct geographic races that are convergent between the species due to mimicry, offering an excellent opportunity to study the genetic basis of phenotypic adaptation.

Richard Wallbank is looking down a microscope

Different races can be crossed together and show that colour pattern divergence has a relatively simple genetic basis – few genes control most of the dramatic colour pattern differences between races. Furthermore, the same genes are repeatedly involved in convergent evolution. Between H. melpomene and H. erato, this is a result of independent evolution of convergent patterns, but in more closely related species this is through exchange of patterns by hybridization.

The different stages of colour pattern development in the pupal stages

This raise the question of why particular genes are targeted by evolution – we hope that by understanding the gene networks that control patterning, we will be able to address this question of why evolution is constrained to particular genetic solutions, but at the same time these few loci can control such a vast array of diversity in patterns.

We are studying the expression of genes during the formation of wing patterns. One gene in particular, cortex, is quite puzzling as a cell cycle family gene – an unlikely candidate for regulating wing patterns.

We have been using CRISPR to study the function of wing patterning genes (Concha et al., 2019), and are now starting to focus on disruption of cis-regulatory elements using the same technology.

The loci that switch between major phenotypic pattern elements are controlled by cis-regulatory elements that have a very modular structure (Wallbank et al., 2016). Particular elements turn genes on in specific regions of the developing wing.

Pigments developing in a pupal wing of Heliconius