(CN) — Long before they flew, the ancestors of insects crawled across the ocean floor. How they evolved wings is a question that’s been debated by scientists for more than a century. Some said wings evolved from an extra leg or outgrowth. Others thought they simply sprang up from the body wall. Research published in Nature Ecology & Evolution on Tuesday confirms both theories.
“People have been wondering that for over 100 years, because that is going to answer some fundamental questions about where do other interesting structures come from?” said the paper’s author Heather Bruce, a molecular biologist who specializes in arthropods. “This leg segment alignment model that I've discovered is the key to opening up all those questions.”
A 10-person team of researchers from the Marine Biological Laboratory in Woods Hole, Massachusetts, compared the genes that form the legs of the marine crustacean Parhyale hawaiensis with the legs of fruit flies, flour beetles and other insects. They discovered not only that the crustacean and insects shared six leg segments and six common genes, but also that the crustacean’s seventh leg segment becomes the body wall in insects during development.
“Much of the insect body wall is derived from leg segments,” the study authors write. “We propose that both the leg exite and body wall theories are correct, but each is relevant to different phylogenetic timepoints: crustacean leg exites evolved into body wall lobes, and then subsequently into wings.”
Some theorize the movement of the seventh leg segment helped support life on land, when those arthropods transitioned out of the sea some 300 million years ago. Meanwhile, sea-dwelling crustaceans maintained their seven legs segments.
"People get very excited by the idea that something like insect wings may have been a novel innovation of evolution," said Nipam Patel, director of the Marine Biological Laboratory in a statement. "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."
Until recently, many scientists believed flying insects were more closely related to millipedes and centipedes, rather than crabs and shrimp. And Bruce said she wants to apply her method to solve how the leg segments relate among other subphylum that include spiders and horseshoe crabs.
“I want to align insect and crustacean legs with myriapod and chelicerate legs,” Bruce said. “Then that would be this really nice, unified framework for understanding arthropod appendages.”