Butterflies Lose Their Luster if Their 'Paintbrush Genes' Aren't On

Butterflies sport a wide range of colors and patterns on their wings, and now we know the genes responsible for their artistic appearance. Matee Nuserm/Shutterstock

The wings of butterflies are delicate, beautiful works of nature. The genes responsible for creating such stirring patterns and colors have been shrouded in mystery, but thanks to two new studies, we've discovered that it's really two genes creating these masterpieces.

That's right. Two. There are two genetic da Vincis that do most of the work on the canvases that are butterflies' wings. These two genes are in fact so important to butterflies' distinct colors, that if you were to turn off the two genes, the colors become either duller or simply monochromatic.

"The two different genes are complementary. They are painting genes specialized, in a way, for making patterns," Arnaud Martin, a developmental biologist at George Washington University and lead author of one of the studies, explained to Nature.

CRISPR colors

The two genes, WntA and optix, had previously been shown to play a part how butterflies' wings' patterns and colors, but it wasn't until scientists switched on and off the genes using the CRISPR-Cas9 technique that they discovered just how big a part the aptly named "paintbrush genes" played.

The study that focused on WntA turned off the gene in seven different butterfly species, including the iconic monarch butterfly (Danaus plexippus). To track and understand the changes, researchers found and disabled the WntA gene in caterpillars, before they had an opportunity to become butterflies. The result was that colors bled into one another, wing patterns were altered in some way or patterns on the wing simply disappeared. In the case of monarchs, their black edges turned gray.

Martin, who headed up the WntA study, equated what he and his team saw to an activity that many of us have done before to learn our colors or how to paint inside the lines. "[WntA is] laying the background to be filled in later. Like color by numbers or paint by numbers. It's making the outlines."

So, without WntA working, other genes that work to actually fill in the colors seem to become less focused on their tasks. They're not like a 5-year-old hopped up on sugar who just really loves that green marker and is scrawling it all over the page, but they are struggling to stay inside the lines and use the right color.

Meanwhile, the study that turned off optix found out just how important the gene was for colorization. Optix had been suspected of playing a part in color patterns, but it hadn't been confirmed until researchers used CRISPR to simply stop it from working.

With optix turned off, parts, if not the whole body, of a butterfly turned black or gray. The results were startling, to say the least. "It was the most heavy-metal butterfly I've ever seen," lead researcher and associate professor at Cornell's department of ecology and evolutionary biology Robert Reed told the Atlantic.

But turning a butterfly into the front man for Black Sabbath wasn't the only thing a turned off optix did. In some cases, the lack of functioning optix resulted in wings displaying a bright and decidedly not heavy metal iridescent blue. In addition to the color difference, iridescence requires a structural change on the wing scales themselves, something Reed and his team noticed when they put the wings under a microscope. According to Reed, the finding adds to "emerging evidence to show that [optix] has probably played a huge role in wing evolution."

Making the wings what they are

Two common buckeye butterflies
How well would these common buckeye butterflies survive if they were a little more blue?. J.R. Sosky/Wikimedia Commons

If you were wondering why this research mattered, Reed's point about wing evolution is key. Colors, patterns and even the wings' structure play a part across a butterfly's existence. And these changes have evolved over thousands of years to benefit their species.

"We know why butterflies have beautiful colored patterns. It’s usually for sexual selection, for finding a mate, or it's some kind of adaptation to protect themselves from predators," White told New Scientist.

But now imagine if WntA or optix didn't work like they were supposed to, or if their functions somehow changed. Reed provided an example of sorts to the Atlantic. Remember the butterfly that became a shiny blue? That was the common buckeye butterfly, known for its splashes of orange and eyespots. Not only did its orange stripes go blue, but parts of its wings did as well.

"With one gene, we could turn this little brown butterfly into a morpho," Reed said. Through this, Reed and his team discovered that the buckeye has the potential for that iridescent look, but that optix represses it in favor of a matte finish.

What would these changes mean in the wild? Would these butterflies be more vulnerable to predators should optix or WntA not work as well, or attempt to mate with the wrong species? While this is a pessimistic consideration, White's point in the video above, however, points to a more optimistic and exciting avenue for this research: Learning more about what a single gene can do to an organism. Determining the functions of those genes can give us new insights into the evolution of different species.