INSECTS first evolved wings around 400 million years ago, and winged insects have thrived ever since. But how did that crucial first step happen?
Biologists have debated several rival ideas for over a century, but no fossil insects with “proto-wings” have been found, so there have been no conclusions. Now two groups have used the gene-editing method CRISPR to narrow down the possibilities.
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and at the University of California, Berkeley, looked at how insects evolved from crustaceans. Insects have six leg segments, but most crustaceans have seven, so insects lost at least one.
Bruce used CRISPR to disable leg genes in a crustacean called , to find which segments relate to parts of the insect body. They found this only made sense if modern crustaceans and insects had a common ancestor with eight leg segments. Modern crustaceans lost one segment, but for insects, two fused with the body, and the wings evolved from them ().
at Miami University in Ohio and his colleagues have also used CRISPR to disable the genes in P. hawaiensis that correspond to wing genes in modern insects. He used other genetic techniques to make the flour beetle Tribolium grow wings on its abdomen, tracing which tissues give rise to them. These studies show that two tissues that are quite separate in crustaceans merge to form the wings of insects ( and ).
“Two distinct tissues are cooperating to form one structure,” says Tomoyasu. This “dual origin hypothesis” was first proposed in 1916, but until recently it was just one of several rival ideas.
“Maybe wings evolved in treeliving insects that glided to safety when threatened”
The new studies, plus , support the dual origins hypothesis, but Bruce’s study suggests the process was more complex than originally envisaged.
“The papers fairly conclusively show the developmental origins of wings in insects,” says at the University of Guelph in Canada.
However, they don’t tell us why wings evolved. One idea is that wings evolved in insects that walked on water and harnessed the wind to sail across the surface. Alternatively, maybe wings evolved in tree-living insects that glided to safety when threatened.
This article appears in print under the headline “Origin of insect wings revealed by gene editing”
