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Don’t It Make My Black Wings Red?

Many tropical butterflies and moths have strikingly beautiful wing colors and patterns. To scientists, though, studying these colors and patterns is less about beauty and more about learning how some butterflies and moths have managed to evolve deceptively similar or exceptionally diverse color patterns.

When butterflies mimic the wing patterns and colors of other butterflies who successfully avoid predators, for instance, how does this work at a genetic level? Is mimicry the result of a simple genetic switch turned on in each species to yield similar wing patterns? Or is the genetic programming much more complex than that?

Heliconius butterfly
Heliconius butterfly (center) with a zoomed in image of wing scale color and pattern (left) and its corresponding stained wing pattern (right) with darker purple areas denoting where the optix gene is expressed prior to red pigmentation.

In a paper published Thursday, July 21, in Science, Dr. Heather Hines, an NC State post-doctoral genetics researcher, and collaborators show that an eye gene called optix appears to be responsible for the red patterns in tropical Heliconius butterfly wings. The authors made the discovery by comparing the genes that are turned on in butterflies with different color patterns. The somewhat surprising proof of this single gene’s role came when – in a stage of development before color was produced – the researchers stained wings wherever optix occurred. They found the staining exactly matched the future distribution of the red pigments – so well, in fact, that they could identify species by the staining pattern alone.

“We finally found the gene switching these patterns on and off, but we also determined that this gene is being used across a diversity of butterflies, suggesting that a common genetic mechanism is employed across mimetic butterflies to yield the same pattern,” Hines says.

Optix is otherwise known only for its role in eye development, Hines adds, which adds further intrigue to the study. Why would an eye gene be responsible for wing colors or patterning? Hines and her colleagues have a guess: The red pigments that optix turns on are called ommochromes, pigments best known for their use as filtering pigments in the eye. Production of optix outside its typical location could lead to the production of “eye” pigments in the wing. Further, Heliconius male butterflies prefer their own color pattern in mates, raising the possibility that optix could be programming both color pattern and visual mate preference.

Hines collaborated on the study with researchers from the University of California-Irvine, who led the study, as well as former NC State genetics professor Dr. W. Owen McMillan, who now works at the Smithsonian Tropical Research Institute in Panama City, Panama.