![]() ![]() ![]() ![]() The researchers then put the butterfly wings under the microscope. The experiment actually involved eight generations total, though, because two generations saw low numbers of offspring and were simply allowed to mate randomly to build up the numbers again.) (Six generations in this species take less than a year. AdvertisementĪfter six generations of selective breeding, the peak reflection had shifted well into the purple at 400nm. They repeated the process of mating and measuring reflection for five additional generations. But the peak was broad and varied from individual to individual, so the researchers selected the males and females that had the peak shifted closer to the visible spectrum, then mated them to produce the next generation. This showed a peak of reflection at 300nm wavelengths, well within the UV range of the spectrum. The researchers started by checking the absorption spectrum of their existing lab strain of butterflies. And two members of the genus have evolved purple pigmentation in the past, suggesting that a color change was within the realm of possibility. "Squinting brown bush" coloration is a bit more complex than the human eye would lead us to believe, in that the butterfly's wings also readily reflect ultraviolet light. Several traits made this species a desirable choice for the work, not the least of which was practicality-it's easy to grow them in dense colonies in the lab. The species chosen for this work was Bicyclus anynana, an African species that also goes by the name of "squinting brown bush." As the name implies (and the image above shows), the majority of its pigmentation is brown, with a few prominent eye spots. In just six generations of selection, they took a brown butterfly and shifted it to a rich, purple color. Now, researchers have tested just how readily these complex optical systems can evolve. Their wings and features have incredibly fine, microscopic features that can help channel light and create interference patterns that enhance some wavelengths while suppressing others. For most forms of life, coloration is synonymous with the presence of a pigment that absorbs some wavelengths and reflects others. ![]()
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