These are different butterflies photographed in daylight (first and second rows) and through an ultraviolet filter (third row). Heliconius (left) are colorful in the ultraviolet while those of mimetic Eueides (right) are colorful only in visible light. New research suggests that the ability of Heliconius butterflies to detect ultraviolet color could help them identify their compatriots in a world of mimics. Credit: Adriana Briscoe/UCI ©

Several species of butterflies have evolved a resemblance to butterflies from the genus Heliconius, which are toxic and bad-tasting to avian predators. The mimics' resemblance to their toxic cousins helps keep the birds at bay, but if the disguises are good enough to fool predators, how do the butterflies themselves tell who's who when it comes time for mating? The answer, according to research led by Seth Bybee (U.C. Irvine and BYU), is ultraviolet pigment—and the ability to distinguish it. Bybee and his colleagues found that some species of Heliconius have two copies of a gene known as the UV opsin gene. "Opsins are part of the visual pigments that allow animals to see, and the duplicated genes allow Heliconius to discriminate ultraviolet colors better than other butterflies," Bybee said. Heliconius wings also reflect ultraviolet-yellow, the researchers found, making them conspicuous to the Heliconius visual system, but not to the visual systems of other butterflies. "The enhanced ultraviolet vision, together with the ultraviolet-yellow wing pigments may allow poisonous Heliconius butterflies a private communication channel for members of their own species, while still allowing butterflies to fool their predators," Bybee said.

###

Seth M. Bybee, Furong Yuan, Monica D. Ramstetter, Jorge Llorente-Bousquets, Robert D. Reed, Daniel Osorio, Adriana D. Briscoe, "UV Photoreceptors and UV-Yellow Wing Pigments in Heliconius Butterflies Allow a Color Signal to Serve both Mimicry and Intraspecific Communication." The American Naturalist 179:1 (January 2012).

University of Chicago Press Journals: http://www.journals.uchicago.edu