We used artificial selection on a laboratory model butterfly, [Bicyclus] anynana, to evolve violet scales from UV brown scales and compared the mechanism of violet color production with that of two other Bicyclus species, Bicyclus sambulos and Bicyclus medontias, which have evolved violet/blue scales independently via natural selection.
Bethany Wasik and her coauthors started with a population of brown B. anynana and measured how well their wings reflected blue light, then bred only the individuals whose wings reflected the most blue. After eight generations, with six repetitions of the selective procedure, the butterflies in the experimental population had wings that shimmered blue.
Wasik et al. found that the color change is due to changes in the nanoscale structure of the scales on the butterflies’ wings—in many other species, blue coloration is usually created in this manner (as opposed to black or red coloration, which tends to be due to pigmentation). These changes in the selected B. anynana population also recapitulated differences between brown B. anynana and some closely related Bicyclus species with blue in their wings.