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Island insects abandon the ability to fly, and Darwin knew why

Island insects abandon the ability to fly, and Darwin knew why
On the Southern Ocean Islands, small islands found halfway between Antarctica and Australia, flies that walk and moths that crawl, like the one pictured, are common. Photo by Leihy and Chow/Monash University

Dec. 10 (UPI) -- Though a majority of the world's insects regularly take to the air, a sizable minority have given up the ability. On the small islands found halfway between Antarctica and Australia, nearly all of the insects have abandoned flight.

Like some many evolutionary phenomena, Charles Darwin had a theory for why insects eventually forgo flight.

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New research, published this week in the journal Proceedings of the Royal Society B, suggests he got it right.

"[Darwin] and the famous botanist Joseph Hooker had a substantial argument about why this happens. Darwin's position was deceptively simple," Rachel Leihy said in a news release.

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"If you fly, you get blown out to sea. Those left on land to produce the next generation are those most reluctant to fly, and eventually evolution does the rest. Voilà," said Leihy, a doctoral candidate at the Monash University School of Biological Sciences.

Like Hooker, many scientists have expressed their doubts about the theory. Few, however, have examined the insect diversity found on sub-Antarctic islands, where howling winds are the norm.

"If Darwin really got it wrong, then wind would not in any way explain why so many insects have lost their ability to fly on these islands," said Leihy.

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For the study, Leihy and her colleague Steven Chown used a large, new dataset on insects from sub-Antarctic and Arctic islands to examine possible explanations for the prevalence of flightlessness.

Leihy and Chown examined faunal inventories, species' morphological information and environmental variables across 28 of the so-called Southern Ocean Islands.

They found flightlessness was more common among insects that evolved on the islands than those that were more recently introduced. They also found insects were more likely to forego flight in the windiest environs.

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Constant high winds make flight difficult and physiologically taxing, causing insects to save their evolutionary capital and invest in reproduction instead of wings and wing muscles.

"It's remarkable that after 160 years, Darwin's ideas continue to bring insight to ecology," said Leihy, lead author of the new paper.

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