Most insects can fly.
Yet dozens of species have lost this extraordinary ability, especially on islands.
On the small islands halfway between Antarctica and continents like Australia, almost all insects have done so.
Flies run, moths crawl.
“Of course, Charles Darwin knew about this wing loss habit of island insects,” says PhD student Rachel Leihy of the Monash University School of Biological Sciences.
“He and the famous botanist Joseph Hooker had a major argument about why this was happening. Darwin’s position was deceptively simple. When you fly you will be blown into the sea. Those who stay on land to produce the next generation are the ones who fly the least, and eventually evolution does the rest. Voilà. “
But since Hooker raised his doubts, so have many other scientists.
In short, they just said Darwin got it wrong.
A flightless moth related to moths from sub-Antarctic Marion Island in the Southern Ocean. The sub-Antarctic islands have an unusually high prevalence of flightless insects. Photo credit: Leihy & Chown.
Yet almost all of these discussions have ignored the epitome of flight loss – these “sub-Antarctic” islands. They are in the “roaring forties” and “angry fifties” and are some of the windiest places on earth.
“If Darwin really got it wrong, the wind would in no way explain why so many insects have lost their ability to fly on these islands,” Rachel said.
Using a large new dataset on insects from sub-Antarctic and Arctic islands, Monash University researchers examined every idea proposed to account for loss of flight in insects, including Darwin’s wind idea.
They reported in Proceedings of the Royal Society B on December 9, 2020 and showed that Darwin was right for this “windiest place”. None of the common ideas (like those suggested by Hooker) explain the extent of flight loss in sub-Antarctic insects, but Darwin’s idea does. Although in a slightly varied form, in keeping with modern ideas about how flight loss actually develops.
Wind conditions make it difficult for insects to fly and are energetically expensive. Therefore, insects no longer invest in flight and its expensive underlying machinery (wings, wing muscles) and redirect resources to reproduce.
“It is noteworthy that after 160 years, Darwin’s ideas continue to provide insight into ecology,” said Rachel, the paper’s lead author.
Professor Steven Chown, also from the School of Biological Sciences, added that Antarctica is an exceptional laboratory for solving some of the world’s most persistent puzzles and testing some of its most important ideas.
Reference: “Wind plays an important, but not exclusive, role in the spread of insect flight losses on remote islands” by Rachel I. Leihy and Steven L. Chown, December 9, 2020, Proceedings of the Royal Society B.
DOI: 10.1098 / rspb.2020.2121
