The Cellular and Genetic Basis for Structural Color in Butterflies*

Research into the optical properties of structurally colored butterfly scales has been remarkably successful and revealed a great deal about the physical basis of color production in a myriad of species. Most of the studies are focused on adult scales, and often driven by the desire to eventually engineer these color-producing nanostructures using non-biological approaches. Our emphasis has been to understand how biological systems, in this case individual scale cells, are able to produce specific structures, particularly how these cells are able to pattern intracellular membranes and other cellular component to create the templates for the nanostructures. We have focused primarily on two systems.
1. Achillides (Peacock) swallowtails. We have investigated the developmental basis for the production of these scales by examining the cytoskeleton during pupal stages. We find that actin structures form as in any typical scale, but then undergo a remarkable reorganization to form a hexagonal array, which prefigure the eventual dimples. We are developing a number of live imaging techniques, combined with integration of fluorescent compounds used to monitor actin assembly, to understand how these hexagons are formed.
2. Structural color in the Buckeye, Junonia coenia. Most populations of Buckeyes have little or no blue or green coloration outside of the center of their eyespots. We are utilizing an artificial line that displays a stunning blue and green iridescence across large portions of the dorsal wings, which appears to be due to a simple thin film structure. We have begun a genetic mapping approach (Quantitative Trait Loci) to uncover the genetic basis for this structural color, and have shown that the optix gene plays a significant role in controlling the distribution of blue/green scales.