Brilliant animal colors often are produced from light interacting
with intricate nano-morphologies present in biological materials
such as butterfly wing scales. Surveys across widely divergent
butterfly species have identified multiple mechanisms of structural
color production; however, little is known about how these colors
evolved. Here, we examine how closely related species and pop-
ulations of Bicyclus butterflies have evolved violet structural color
from brown-pigmented ancestors with UV structural color.We used
artificial selection on a laboratory model butterfly, B. 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 selec-
tion. The UV reflectance peak of B. anynana brown scales shifted
to violet over six generations of artificial selection (i.e., in less than
1 y) as the result of an increase in the thickness of the lower lamina
in ground scales. Similar scale structures and the same mechanism
for producing violet/blue structural colors were found in the other
Bicyclus species. This work shows that populations harbor large
amounts of standing genetic variation that can lead to rapid
evolution of scales’ structural color via slight modifications to
the scales’ physical dimensions
Brilliant animal colors often are produced from light interactingwith intricate nano-morphologies present in biological materialssuch as butterfly wing scales. Surveys across widely divergentbutterfly species have identified multiple mechanisms of structuralcolor production; however, little is known about how these colorsevolved. Here, we examine how closely related species and pop-ulations of Bicyclus butterflies have evolved violet structural colorfrom brown-pigmented ancestors with UV structural color.We usedartificial selection on a laboratory model butterfly, B. anynana,to evolve violet scales from UV brown scales and compared themechanism of violet color production with that of two otherBicyclus species, Bicyclus sambulos and Bicyclus medontias, whichhave evolved violet/blue scales independently via natural selec-tion. The UV reflectance peak of B. anynana brown scales shiftedto violet over six generations of artificial selection (i.e., in less than1 y) as the result of an increase in the thickness of the lower laminain ground scales. Similar scale structures and the same mechanismfor producing violet/blue structural colors were found in the otherBicyclus species. This work shows that populations harbor largeamounts of standing genetic variation that can lead to rapidevolution of scales’ structural color via slight modifications tothe scales’ physical dimensions
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