In an initial study, the team used master switches in the beetles’ genome to manipulate which segments of the body had wings. To their surprise, doing so disrupted portions of anatomy that had seemed unconnected to flight.
This offered some support for the idea that wings were composite tissues. But how might the ancestral wing structures have formed?
The researchers turned their attention to the pupae, which have defensive sets of miniature pincers along their abdomens. These so-called gin-traps sit near the top of the insect, which make them likely models for early wing structures.
To add support for the dual origin hypothesis, Dr. Linz said, evolution would have had to fuse a structure on the dorsal region of the segment and one from the pleural tissue.
The team introduced a fluorescent green protein into the beetles that marked the expression of certain wing-related genes, making it easy to tell which tissues were being affected by genetic tampering. After manipulating genes of the abdomen, they were delighted to see two green tissues: one at the dorsal gin-trap, and one down in the pleural tissue.
And by doing so, they were able to produce pupae in which both tissues fused to form pairs of tiny wings.
“They’re obviously very, very sick, because that’s not how they normally develop,” Dr. Linz said. “They frequently just die, so sadly I was never able to produce an adult beetle with 10 pairs of wings.”
Credit David M. Linz and Yoshinori Tomoyasu
While he found the study interesting, Dr. Shockley said the idea that embryonic or larvae development is like a fast-forwarding tape of prior evolutionary modifications has largely been discredited.
Still, he acknowledged that manipulating gene expression is useful for trying to piece together details of structures that are hard to visualize.
“I would like to see if they could get a third pair of wings to express,” Dr. Shockley said. “There’s been additional debate about whether proto-insects would have actually had three pairs of wings and then lost the first pair, perhaps to deal with aerodynamic instability from three sets of wings beating instead of just two.”
The debate about how insect wings evolved is far from over, Dr. Tomoyasu said. “We’re still relying on one species,” he said. “Although we see that there are two tissues that are contributing to make wings, that could be unique to this lineage.”
”It’s crucial for us to study more insects,” he added. “In my lab, we’re now studying cockroaches and some crustaceans to see if the process repeats the same way.”
In the meantime, he holds out a bit of hope that the fossil record someday might help solve the mystery.
“We are very confident about our analyses, but it’s a prediction,” he said. “It would be very cool to actually see the shape of an ancestral insect.”