Wing venation and Distal-less expression in Heliconius butterfly wing pattern development.

Here we show that major color pattern elements of Heliconius butterfly wings develop independently of wing venation. We recovered a hybrid Heliconius displaying a mutant phenotype with a severe vein deficiency. Although this butterfly lacked most of its wing veins, the large, melanic banding patterns typical of the genus were conserved across the entire wing. The only obvious correlation between vein reduction and pigment patterns was a loss of vein-associated melanin stripes near the distal margin of the wings. We examined the expression of the eyespot-associated transcription factor Distal-less in a banded and a spotted species of Heliconius and found no obvious relationship between protein expression and the band or spot patterns typical of the genus. Together, our results suggest that the melanic bands and spots in Heliconius are unlikely to be derived from an eyespot determination system. We propose that major elements of Heliconius wing pattern formation are based primarily on a complex, whole-wing proximodistal axis system.