Butterflies have evolved numerous wing colors over millions of years due to variations in the thickness of the films coating their wing scales, according to a study published on April 7 in eLife. The researchers measured these films, or laminae, in nine species of Junonia butterflies and Precis octavia. Structural colors arise from light being scattered by highly refractive materials, such as the chitin found in scale lamina, the authors write. When buckeye butterflies (J. coenia) were artificially selected for blue wing color, their laminae were found to be 74 percent thicker than that of wildtype butterflies with brown scales.
“It was a surprise to find that the lamina, a thin sheet that looks very simple and plain, is the most important source of structural color in so many butterfly wing scales,” says coauthor Rachel Thayer of the University of California, Berkeley, in a press release. “In each Junonia species, structural color came from the lamina. And they are producing a big range of lamina thicknesses that create a rainbow of different colors, everything from gold to magenta to blue to green.”
R.C. Thayer et al., “Structural color in Junonia butterflies evolves by tuning scale lamina thickness,” eLife, doi:10.7554/eLife.52187, 2020.