Dec. 1 (UPI) -- Combining old studies with novel genomic analysis, researchers have finally figured out how insects first developed wings.
According to a new paper published Tuesday in the journal Nature Ecology and Evolution, insect wings evolved from an outgrowth, or lobes, on the legs of an ancestral crustacean.
Roughly 300 million years ago, when the marine crustacean species Parhyale hawaiensis transitioned to life on land, its uppermost leg segments were incorporated into its body wall during embryonic development.
"The leg lobes then moved up onto the insect's back, and those later formed the wings," study co-author Heather Bruce said in a news release.
Roughly a decade ago, genomic analysis proved insects were closely related to crustaceans, the group of arthropods that includes crabs, lobsters, shrimps, krill and barnacles.
"Prior to that, based on morphology, everyone had classified insects in the myriapod group, along with the millipedes and centipedes. And if you look in myriapods for where insect wings came from, you won't find anything," said Bruce, a researcher at the Marine Biological Laboratory in Woods Hole, Mass.
Scientists theorized that insect wings were an entirely novel structure -- a feature without a morphological antecedent.
"People get very excited by the idea that something like insect wings may have been a novel innovation of evolution," said MBL director and study co-author Nipam Patel.
"But one of the stories that is emerging from genomic comparisons is that nothing is brand new; everything came from somewhere. And you can, in fact, figure out from where," Patel said.
While comparing the genes controlling leg segmentation among one crustacean and two insect species, the beach-hopper Parhyale, fruit fly Drosophila and the beetle Tribolium, Bruce noted strong similarities.
She used CRISPR-Cas9 gene editing to disable genes responsible for leg segmentation in the insects, and her experimentation showed the genes controlled to the six leg segments located farthest from the body wall.
However, Bruce also found Parhyale possessed a seventh leg segment closest to its body wall.
"And so I started digging in the literature, and I found this really old idea that had been proposed in 1893, that insects had incorporated their proximal [closest to body] leg region into the body wall," she said.
Bruce continued digging and found another more advanced theory, proposed in the 1980s, that posited lobes on the newly incorporated leg region moved onto the backs and insects and eventually formed wings.
"I thought, wow, my genomic and embryonic data supports these old theories," Bruce said.
According to Bruce and Patel, the leg segmentation genes shared by crustaceans and insects show insect wings are not novel structures -- they evolved from ancestral structures.
