Single master regulatory gene coordinates the evolution and development of butterfly color and iridescence

Significance The optix gene is well known for its genetic association with wing pattern variation in butterflies; however, its actual function has never been directly confirmed. Using CRISPR genome editing in multiple butterfly species, we show that this gene plays a fundamental and deeply conserved role in the butterfly family Nymphalidae, where it acts as an activator of wing color. We were also surprised to discover that optix simultaneously controls blue iridescence in some species as well, providing an example of how a single gene can act as a switch to coordinate between structural and pigmentary coloration.