Figure 6.

Co-option followed by diversification of Optix-positive patterns. Optix co-option into color scale cell precursors occurred prior to the Heliconiini radiation, notably resulting in ancestral patterns of the proximal complex (white box). These novel patterns subsequently diversified by cis-regulatory evolution of optix expression (as shown in branches marked by green bullets) and by changes at epistatic loci (see Discussion), explaining repeated diversifications of red patterns in the Eueides and Heliconius lineages. Finally, introgressions of optix alleles fostered the distribution of novel alleles between species, as shown in the melpomene-cydno-silvaniform clade (yellow box). The phylogenetic sampling and the associated insets highlight the diversification of ventral Optix-positive patterns, but similar principles apply to the dorsal side. Asterisks: species with known Optix expression. Current phylogeny [67] places Optix-positive vein scales observed in male Dryas and Agraulis as an ancestral, sexually dimorphic feature of Heliconiini, suggesting a co-option event followed by a secondary loss in the Euiedes-Heliconius lineage.