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Walking Stick With Wings

Walking stick species <em>Phasma gigas</em> with wings

A Brigham Young University (BYU) study found that some walking stick species like this foot-long Phasma gigas, native to Papua New Guinea, re-evolved wings after losing them 50 million years earlier. Walking sticks, a group of insects that mimic twigs to stay hidden from predators, are the only organism known to have re-evolved a complex trait. [Image 2 of 5 related images. See Image 3.]

More about this Image
In January 2003, Michael Whiting, a Brigham Young University (BYU) professor of integrative biology announced that he and his colleague, Taylor Maxwell, had discovered genetic evidence that indicates many species of walking sticks lost their ability to fly but then re-evolved the capacity 50 million years later. Walking sticks are a group of insects that mimic twigs to stay hidden from predators. Their findings were reported in the Jan. 16, 2003, cover article of the scientific journal Nature.

Whiting and Maxwell, a BYU undergrad assigned to stick insects at the time of the study, first began working together when Whiting received a $1.34 million grant (DEB 01-20718) from the National Science Foundation (NSF) to construct the family tree of the insect class. He asked Maxwell to sequence and analyze the DNA of 35 species of walking sticks as part of the broader study to determine which evolved first. Maxwell, who was supported by grants from BYU and NSF designed to facilitate undergraduates' participation in research, put together preliminary results. The study found that some species of walking sticks without wings existed before their winged descendants.

These findings shook up the evolutionary research field because it was the first time any organism had been shown to have re-evolved a complex trait, something scientists previously thought impossible. In the evolutionary process, it is believed that complex functions such as flight or sight, if not used, will evolve out of a species. The Encyclopedia of Evolution cites "Dollo's Law"--the principle that organs or complex structures cannot return to a condition seen in an ancestor.

Entomologists have documented many cases where species of insects have lost their ability to fly. For example, an insect whose habitat may change over time would evolve to survive more easily in the habitat. Whiting suggests that walking sticks may have lost wings to help them blend in with their surroundings. He also noted that wingless insects have been shown to lay more eggs than their winged relatives. This could have been important for walking sticks because instead of burying their eggs in the ground as similar species do, they drop them to the earth from their homes in the treetops. And the more eggs the wingless walking stick produces, the more chances it has to pass along genes to the next generation.

For whatever reason, some 50 million years ago, it was advantageous to have some of the species become winged again. Now there are various species of winged and wingless walking sticks. What's remarkable is that they had the ability to generate wings when they needed them. (Year of image: 2003)

Credit: Insect Molecular Genomics Lab, Brigham Young University; photo by Allison Whiting/BYU

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