Melanin Pathway Genes Regulate Color and Morphology of Butterfly Wing Scales

The cuticular skeleton of a butterfly wing scale cell is an exquisitely finely sculpted material that can contain pigments, produce structural colors, or both. While cuticle rigidity and pigmentation depend on the products of the melanin pathway, little is known about whether genes in this pathway also play a role in the development of specific scale morphologies. Here, we use CRISPR/Cas9 to show that knockout mutations in five genes that function in the melanin pathway affect both the fine structure and the coloration of the wing scales. Most dramatically, mutations in the yellow gene lead to extra horizontal laminae on the surface of scales, whereas mutations in DDC gene lead to taller and sheet-like vertical laminae throughout each scale. We identify genes affecting the development of color and scale morphology, the regulation and pleiotropic effects of which may be important in creating and limiting the diversity of the structural and pigmentary colors observed in butterflies.