Key Gene That Influences The Pattern Of Butterfly Wings
There are more than 18,000 named butterfly species on the planet today, and about 140,000 different moth species. All of them evolved from a common ancestor that lived more than 225 million years ago. From that one ancestor, a parade of colours and shapes have burst forth, populating forests, savannahs, fields and gardens with patterns and textures. Each species has developed a strategy to make the most of their biggest asset and defining feature: their scaly wings.
Now, scientists have unlocked what causes these butterflies to obtain unique, distinguishable colors and patterns of their own.
Using CRISPR/Cas9 gene editing tools, researchers knocked out a gene called WntA in embryos from seven different butterfly species, essentially turning it off. The resulting adult butterflies developed changes in wing patterns and colors that differed in each species, suggesting that while WntA plays a fundamental role in wing patterning across butterfly species, it has been used in a variety of ways.
“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,” Dr. Arnaud Martin, an assistant professor of biology in the George
Washington University’s Columbian College of Arts and Sciences. “What is more mysterious is how do they do it. How do you make stripes and dots, how do you make complexity, how do you fine-tune a given feature during long evolutionary time scales?”The studies focused on two genes previously identified as being key in butterfly wing pattern development. Called WntA and optix the researchers have described these as “painting genes” and across several experiments they observed what happens in different butterfly species when each gene is selectively switched off.
The team examined the WntA gene and discovered that with the deletion of the WntA gene with the Crispr technique, the central symmetry system band disappears entirely from the wings of the speckled wood and buckeye butterflies. But in other species, the loss of WntA has very different effects, suggesting that the gene has been adapted many times to play different patterning roles as new butterfly species evolved.
Marcus Kronforst, PhD, associate professor of ecology and evolution at the University of Chicago and an author on the stud and Darli Massardo, PhD, a postdoctoral fellow at UChicago, worked with monarch butterflies. The loss of WntA caused the monarch’s characteristic orange scales to turn white, but didn’t change the overall pattern of the wings. Another team worked with painted lady butterflies, which lost the usual black spots in the middle of their wings. Other species developed differently shaped bands across the wings.
“When we knock out the gene, we’re seeing totally different effects,” Massardo said. “So, although WntA is involved in wing-patterning in general, it’s doing fundamentally different things in different species.”
Kronforst and Massardo say that the results of this study give scientists insight into the process of evolution, as butterflies exploit the utility of this gene to develop multiple wing patterns. The widespread use of precise genetic tools like CRISPR will allow them to explore this process further, moving beyond simple knockout experiments to more complex, functional changes.
“Now we’re just altering the gene to make it nonfunctional,” Kronforst said. “But what we’d really like to do are things like precisely put in a copy of the same gene from another species or another color pattern and see what that does. This just opens the door for us.”
