By growing wings on the abdomens of beetles, scientists have come a little closer to solving the mystery of how insects developed their wings in the first place.
The origin of insect wings remains a mystery, in large part because we don’t have any fossils that can tell us about the ancestors of today’s creatures (unlike with many mammals that leave behind bones). “The field of evolutionary development is basically an alternative approach to paleontology,” says Yoshinori Tomoyasu, a biologist at Miami University and co-author of the insect wings study published last week in the journal Proceedings of National Academy of Science. “We have a huge gap in fossil record, so the idea is that we try to understand the ancestral state by studying the development of modern insects.”
For this study, Tomoyasu and his colleagues edited the genes of the Tribolium beetle so that it would partially grow a wing on its abdomen — a place beetles don’t usually have wings. As a result, they saw that a wing developed from tissues in the leg and the body wall, helping confirm one of the three competing explanations for why insect wings develop.
One theory proposes that a back leg became part of the body and then moved up and became an insect wing. Another suggests that a wing simply grew out of the dorsal (or upper back) side of the body wall. The third — called the “dual-origin hypothesis” — suggests it is a combination of both the leg and the body wall, and is the hypothesis supported by the results from the PNAS paper. “We are able to actually trace which tissue actually transformed into wings,” says Tomoyasu, “and to our surprise we were able to see two tissues merging, so from there, we concluded that, at least in beetles, wings are formed from two distinct tissue.” Plus, a separate paper — this time a pre-print, meaning it has not been peer-reviewed or accepted to a journal — from a group at UC Berkeley that Tomoyasu’s lab communicates with, also supported this hypothesis using different methods.
However, “it is very dangerous to conclude something from only one species,” says Tomoyasu. For a long time, these types of experiments were only done on the fruit fly Drosophila melanogaster. Scientists are still not sure whether the beetle or the fly is closer to the ancestral insect, so it’s important to try this on different insects to see if they’re applicable. (Interestingly, a recent Current Biology paper suggested that tissue from two parts of the fly become wings, adding more support for the dual-origin hypothesis.) Next, Tomoyasu’s lab is working on cockroaches and mayflies, and has written a pre-print paper about shrimp. Shrimp, of course, do not have wings, but they are related to insects, so the lab is trying this method on different creatures. They discovered tissues that would be analogous to wings in insects, and then removed them using the gene-editing technique CRISPR-Cas9.