Parallel evolution of ancient, pleiotropic enhancers underlies butterfly wing pattern mimicry

Color pattern mimicry in Heliconius butterflies is a classic case study of
complex trait adaptation via selection on a few large effect genes.
Association studies have linked color pattern variation to a handful of
noncoding regions, yet the presumptive cis-regulatory elements (CREs) that
control color patterning remain unknown. Here we combine chromatin assays,
DNA sequence associations, and genome editing to functionally characterize
5 cis-regulatory elements of the color pattern gene optix. We were
surprised to find that the cis-regulatory architecture of optix is
characterized by pleiotropy and regulatory fragility, where deletion of
individual cis-regulatory elements has broad effects on both color pattern
and wing vein development. Remarkably, we found orthologous cis-regulatory
elements associate with wing pattern convergence of distantly related
comimics, suggesting that parallel coevolution of ancestral elements
facilitated pattern mimicry. Our results support a model of color pattern
evolution in Heliconius where changes to ancient, multifunctional
cis-regulatory elements underlie adaptive radiation.