Butterfly wings hold clues to evolutionary adaptation

UChicago biologists examine how genetics gives species different traits

Beneath the scales that form the color palette on their wings, butterflies have a clear membrane that is as functional, if not as beautiful, as their flamboyant pigmentation. “Kids learn that if you touch a butterfly, you get the scales rubbed off of them and they can’t fly,” says evolutionary biologist Marcus Kronforst, “but it’s not true, they fly fine.” Some species have even evolved without scales, he adds, the ultimate in fluttering camouflage: “Stealth butterflies.”

Kronforst knows about durability and adaptability. In a campus greenhouse, he studies the genetics of color patterns in two tropical butterfly species as a window into evolutionary variation and adaptation throughout nature. He and his research team raise the butterflies in mesh tents about the size of an office cubicle. They grab them from the air—the scales leave a powdery residue on their fingers—and see them thrive even as their wings fray from flying in the tight confines. The insects are not as fragile as their handle-with-care reputation suggests. “Butterflies,” Kronforst says, “are really robust.”

Their genetic heritage helps make them that way. Some vulnerable butterflies have evolved to mimic the coloring of related species that are toxic to predators. The seven researchers in Kronforst’s lab decode those protective adaptations. As color patterns change, butterflies develop different mate preferences, leading to more than just color variation. “Adaptation is actually causing the origin of a new species,” Kronforst says, referring to a discovery he helped detail in a 2009 Science paper. “We’re trying to tackle these big questions of how organisms adapt and diverge.”

In a breakthrough published last year in Nature, an international consortium, to which Kronforst contributed, sequenced the genome of a species within the Heliconius genus. To their surprise, the researchers found that the Heliconius melpomenebutterfly has identical color-patterning DNA as two other species. They believe hybridization—interbreeding among the species—accounts for the phenomenon.

“Evolutionary biologists often wonder whether different species use the same genes to generate similar traits,” Kronforst told the Harvard Gazettein 2012. “This study shows us that sometimes different species not only use the same genes, but the exact same stretches of DNA, which they pass around by hybridization.”

With that knowledge, researchers can map the genomes of butterflies with different color patterns to identify the relevant genes: Spikes in the data suggest the genetic source for the array on the wings. “If we hadn’t done all that fine detail work over the last years, we wouldn’t know what those peaks were telling us about,” Kronforst says. “But now that we know that’s where the color-patterning genes are, we see these peaks that just jump out.”

Building on those advances and using rapidly evolving techniques, his lab continues moving toward the ultimate goal: to metaphorically rub off the scales and uncover the genetic blueprint underneath.

'Charismatic' subjects to study

Last year Kronforst joined UChicago’s Department of Ecology and Evolution as a Neubauer Family assistant professor, creating a tropical hothouse high above the Donnelley Biological Sciences Learning Center.

Two rooms—one 1,800 square feet, the other 500—maintain tropical heat and humidity levels that simulate the butterflies’ habitat. The adult insects, along with the eggs and larvae, must be contained in the mesh cages to prevent escape, among the USDA requirements for housing the nonnative species.

Under those conditions, Kronforst’s lab orchestrates a perpetual cycle of butterfly life. “Most of the operation is plants,” he says, referring to citrus trees where females lay eggs that hatch into caterpillars before forming chrysalises that yield the next generation of research subjects. His enthusiasm overflows in a flurry of words—a fascination with his insect subjects that he often finds other people share. Butterflies, in and of themselves, Kronforst allows—and agrees—are “charismatic.”

More than their color entrances him, though; he’s drawn to the knotty genetic knowledge they could help untangle. “Our work is aimed at the evolutionary processes of adaptation and speciation,” he says, “and in particular, how these two things interact.”

As the discovery of the emerging new species showed, Kronforst’s research offers an almost real-time view of those processes. “By studying these butterflies we’re able to capture evolutionary events in progress,” he adds, “and that’s something that can be hard to find in nature.”

To read the entire article, visit the University of Chicago Magazine website.