Artificial selection for structural color on butterfly wings and comparison with natural evolution

Area of Science:

• * Evolutionary biology
• * Biophotonics
• * Insect morphology

Background:

• * Brilliant animal colors, particularly in butterfly wings, arise from light interacting with nanoscale structures.
• * While various structural color mechanisms are known, their evolutionary pathways remain largely unexplored.
• * The genus Bicyclus provides a model for studying the evolution of structural color due to its diverse species and known color variations.

Purpose of the Study:

• * To investigate the evolutionary mechanisms behind the development of violet structural color in Bicyclus butterflies.
• * To understand how violet color evolved from ancestral UV structural color in Bicyclus species.
• * To compare the evolution of violet/blue structural color in a laboratory setting with natural evolutionary processes in related species.

Main Methods:

• * Artificial selection was applied to the model butterfly Bicyclus anynana to evolve violet scales from UV-brown scales over six generations.
• * The nano-morphology of scales was analyzed to identify changes in structure responsible for color shifts.
• * Scale structures and color production mechanisms were compared between the experimentally evolved B. anynana and naturally evolved B. sambulos and B. medontias.

Main Results:

• * Artificial selection rapidly shifted the UV reflectance peak to violet in B. anynana scales within six generations.
• * The color shift resulted from an increase in the thickness of the lower lamina in ground scales.
• * Similar scale structures and violet/blue color production mechanisms were observed in naturally evolved Bicyclus species.

Conclusions:

• * Rapid evolution of structural color is possible through subtle modifications of physical dimensions in butterfly wing scales.
• * Populations possess significant standing genetic variation that facilitates rapid adaptation of structural coloration.
• * Convergent evolution of violet/blue structural color occurs via similar nano-morphological changes in related Bicyclus species.