ABOVE: Blue buckeye butterflies were selectively bred to produce iridescent lamina colors on the underside of their wing scales.

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...

A helium ion micrograph of a butterfly scale shows the ridges (R), crossribs (r), and lamina (L). 
R.C. Thayer et al., eLife, 2020
Artificially selected blue buckeye butterfly wings (left) and wildtype brown buckeye butterfly wings (right)

R.C. Thayer et al., “Structural color in Junonia butterflies evolves by tuning scale lamina thickness,” eLife, doi:10.7554/eLife.52187, 2020.

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