Darwin Was Right: Wind Causes Insects to Lose the Ability to Fly

The evolutionary debate has been raging for 160 years.

(CN) — Several winged insects on the small islands surrounding Antarctica are losing their ability to fly — an evolutionary event Charles Darwin predicted 150 years ago.

In the study, published Tuesday in the journal Proceedings of the Royal Society B, lead author and doctoral candidate Rachel Leihy of  the Monash University School of Biological Sciences, looked at this phenomenon of flight loss in association with Darwin’s findings and discovered significant answers.

The study looked at insects from the small subantarctic islands between Antarctica and nearby continents like Australia, where almost all insects have opted for walking — even the most notorious flyers like flies and moths. 

Scientists have seen the loss of flight in insects for years, raising questions as to why evolution would favor the loss of a trait that contributes so much to survival. In the past, flight loss has been attributed to molecular evolution, where due to various external factors an animal’s energy would instead be redirected to reproduction or other functions. A long-lived debate however still exists in the scientific community as to the reasons why.

Leihy looked to Darwin, the famous naturalist and ecologist responsible for contributing the theory of natural selection and evolution, who had some thoughts on flightlessness in his era. Darwin encountered flightless birds in his time on the Galapagos Islands and after observing them, concluded flight simply no longer suited the birds.

For example, in his discovery of the flightless cormorant, he found that although their wings were no longer capable of flight, they were able to maneuver better in the water to catch fish than flying cormorants. They found more success on land and sea than in the air and over time, adapted to fit this need. The same would be true for insects who found more success traveling on foot than through the air, but he had some challengers on that idea.

For their study, Leihy and her team were interested in why this might be happening on these specific sub-Antarctic islands, and suspected weather conditions may play a large role in this evolutionary adaptation. These islands lie within “roaring 40s” and “furious 50s,” latitudes notorious for their extreme and nearly constant winds.

“Of course, Charles Darwin knew about this wing loss habit of island insects,” said Leihy. “He and the famous botanist Joseph Hooker had a substantial argument about why this happens. Darwin’s position was deceptively simple. 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.”

The authors note many scientists followed Hooker’s lead in doubting Darwin’s idea, creating a debate among biologists.

“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.

To investigate their hypothesis, Leihy and the team from Monash University in Australia used a newly developed database containing expansive data on insects from Arctic and sub-Antarctic islands. They considered every possible explanation for the insects’ loss of flight, which included Darwin’s theory on wind discouragement. 

After analyzing all avenues, they concluded that Darwin had it right in predicting that windy environments would dissuade the lightweight flyers from using their wings due to the risk of being blown away.

Furthermore, the more wind there is, the more energy insects will need to exert to control their flight. Therefore, according to the rules of natural selection, insects who choose not to fly would find more success on land, and over time their wings would lose the muscle to take to the air.

This is supported by previous findings of flightless creatures in areas where the cost of flying outweighs the benefit, such as severe cold or strong winds. Flies and other airborne insects can often lose their wings in regions with these conditions.

“It’s remarkable that after 160 years, Darwin’s ideas continue to bring insight to ecology,” Leihy said.

Leihy’s colleague Steven Chown, a professor at Monash, says he believes that the Antarctic region is an extraordinary laboratory in which to resolve some of the world’s most enduring mysteries and test some of its most important ideas.

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