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Scientists have used selective breeding to create purple wings on the normally brown-winged butterfly Bicyclus anynana. Antonia Monteiro and her colleagues selected butterflies with wing scales that reflected light closest to the wavelengths that produce the color violet and bred them. After six generation of breeding, the researchers produced butterflies with wings that had changed structurally to reflect violet light. The research appears in the Proceedings of the National Academy of Sciences.
Living things can produce color chemically or structurally. Those that produce chemical color create pigments that absorb certain wavelengths of light and reflect others. Organisms that produce structural color experience changes in their bodies, at the nanoscale level, that enhance the reflection of particular wavelengths.
Butterfly wings have structural color. To understand how this color evolves, Monteiro and her team selectively bred B. anynana, a butterfly that normally has brown wings, in an attempt to create purple wings. Two close relatives of this butterfly, B. sambulos and B. medontias, have purple scales on the backs of their front wings. However, until now, no one has ever reported seeing any purple-winged B. anynana.
To create purple wings, the team measured the wavelengths of light reflected from the wings of B. anynana specimens. They then selected and bred those butterflies whose wings reflected light closest to the violet spectrum. They performed this process six times in eight consecutive generations. As the breeding process continued, reflected wavelengths moved further toward the violet spectrum. By the sixth time, the butterflies had purple wings.
When the researchers examined the wings that had changed color, they discovered that the thickness of some of the scales had changed. This altered the wavelengths of light the wings reflected. They studied the wings of B. sambulos and B. medontias, which naturally have wings that reflect violet light, and found that some of their wing scales were similar in thickness to those that had changed in the purple-winged B. anynana. However, the types of scales that reflected violet light in B. sambulos and B. medontias were different from the type of scale that had changed in B. anynana.
Monteiro's team believe their experiment shows that butterfly wing colors can evolve very quickly and that natural selection could play an important role in the development of wing color. For example, butterflies could use wing color to identify other butterflies of the same species or to influence mate choice.
Bicyclus anynana before (left) and after (right) artificial selection efforts to produce butterflies with violet wing scales. After selective breeding, the butterflies displayed more violet color in the ground scales of their wings. Credit: Antónia Monteiro
The team says engineers could use these findings when designing devices that tune color, trap light or steer light beams.
Read more at: http://phys.org/news/2014-08-scientists-purple-winged-butterflies.html#jCp
