Walking Sticks Fly Again

Got wings? Some modern stick insects, like this Phasma gigas (top), regained wings, but others, like members of the Leprocaulinus genus (inset) still have to get around on their own six feet.

It's not difficult to lose your wings. Many birds and untold insects have done just that. But now, for the first time, scientists have found evidence that several lineages of stick insects regained the ability to fly. Apparently, the insects kept intact the blueprints for making wings during eons of flightlessness.

Evolutionary theory suggests that when a complex feature like a wing falls out of use, the genes that code for its parts will accumulate so many mutations that they would never work again. That means that once the ancestral walking sticks gave up their wings, their descendants would never be able to fly.

Michael Whiting, an evolutionary biologist at Brigham Young University in Provo, Utah, didn't set out to refute this--he simply wanted build a family tree for the walking sticks because no one knew how they were related to each other and to other insects. Whiting and his colleagues collected 37 kinds of stick insects around the world, sequenced three sections of DNA, and used the sequences to make a phylogenetic tree.

Then Whiting sent the tree to a colleague who knew which species had wings and which didn't. "We noticed this fascinating pattern," Whiting says. Although some kinds of walking sticks had wings, the oldest stick insects didn't. The wings look just like other insect wings, Whiting says, so they weren't re-evolved from scratch--just fashioned from earlier plans inherited from the winged ancestor that gave rise to all walking sticks. Whiting says the insects could probably get wings back because the genetic pathways that make stick insects' wings and legs are closely related. "In order for insects to have legs and still walk around, they have to retain at least a portion of that pathway required to make a wing," he says. The work appears in the 16 January issue of Nature.

Maybe it's not as hard to turn complex structures back on as some scientists thought, says Lisa Nagy, who studies development and evolution at the University of Arizona, Tucson. The change that took wings away and brought them back might have just been in the regulatory areas of genes, she says--not in the parts of genes that make the wing, but in the promoter regions that tell the genes when to turn on. "If their analysis is right," Nagy says, "then it points to a whole new set of experiments that we can do to learn about how pathways change in evolution."

Related sites
Whiting's lab
Information on stick insects from the Australian Museum
Stick insects from the Entomological Database of Very Cool Bugs
How to take care of stick insects, from The Bug Club in the United Kingdom

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