The Antarctic midge spends more than half its life frozen. A better understanding of how it does so could have implications for human health.
There are between five million and six million insect species worldwide, and scientists have described about one million of them. Of these, only one, the Antarctic midge, is able to survive at the bottom of the planet. Purplish, wriggly and the size of a pinkie fingernail clipping, Antarctic midge larvae live for nearly two years underground, often near penguin and seal excrement. They spend over half of their lives, about eight months of the year, frozen.
Nicholas Teets, who leads the Insect Stress Biology Lab at the University of Kentucky, published an article last month in the Journal of Experimental Biology that reveals how Antarctic midge larvae are able to survive such extremes. By better understanding the processes at work, scientists hope that the Antarctic midges’ survival strategies — including dehydration and freezing — might have applications for the preservation of human tissues, such as organs harvested for transplants.
Researching the Antarctic midge isn’t glamorous. If you want to find one, the easiest place to look in Antarctica is where nitrogen fertilizer has accumulated. Dr. Teets and his colleagues crawl through seal and penguin guano to collect midges with spoons and bags.
“They’re not visually appealing,” Dr. Teets said of the midges, and the smell “is pretty awful.”
Back in the lab, Dr. Teets and his team study how the larvae are able to survive such punishingly cold weather.
Leslie Potts, a graduate student in entomology at the University of Kentucky, accompanied Dr. Teets to Antarctica in 2017 and plans to return there next year. Antarctic midges, she said, are the “Olympic gold” of insects, having adapted to survive intense winters.
Midges are the largest purely land animals in Antarctica (seals and penguins spend part of their lives in the water) and champions of multiple extremes. The larvae can survive being frozen at temperatures as low as -15 degrees Celsius; immersion in fresh or saltwater, and the loss of up to 70 percent of their body fluids. They can also go without oxygen for as long as a month.
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When the midge larvae are dehydrated, “they look like little raisins” said Rick Lee, a professor emeritus at Miami University in Ohio. “You can’t imagine that they’re alive. And then you drop them back into fresh water — they plump up and they wriggle away. I always say I think I can hear them laughing at us because they are so used to dealing with these stresses. They are super-tolerant.”
In any other creature, these adaptations would be astounding. “These are things that humans could never do,” said Yuta Kawarasaki, a biologist at Gustavus Adolphus College in Saint Peter, Minn., and a co-author of the study.
So how does the Antarctic midge do it? Part of the answer lies in its microhabitat. Whereas the air temperature in Antarctica routinely drops below -20 degrees Celsius, the temperature beneath the soil and snowpack, where midge larvae live, is just a few degrees below zero. When the midge larvae experience cold, the icy environment creates a gradient for water loss, extracting water from their bodies. Some larvae are able to lose enough water that they don’t freeze at all.
“The wetter a site is, the more likely they’re going to freeze,” said Michael Elnitsky, a biologist at Mercyhurst University who wrote his dissertation on arthropods in Antarctica. Some midges live on islands with grainy, sandy soils that dry up. Others live in areas with moist moss beds. “In a more dry environment, they use the dehydration strategy to survive the winter,” he said.
Another tool at the Antarctic midge’s disposal is rapid cold hardening. Insects and other coldblooded animals (think fish and toads) can quickly change their physiology when the temperature drops to boost their tolerance to cold.
The exact mechanics of this process are still mysterious. There seem to be changes, though, at the level of individual cells. As the midge’s cells cool, some of their properties change, causing calcium to enter. Dr. Teets knows from past research that if calcium is prevented from entering cells, the organism is no longer able to perform rapid cold hardening. The calcium itself isn’t protective, but it functions like a switch that causes other important things to happen.
Joanna Kelley, an evolutionary geneticist at Washington State University, helped to sequence the Antarctic midge genome in 2014. Her research showed that the Antarctic midge has a very small genome — the smallest reported for an insect at the time — with few repetitive elements. Dr. Kelley also identified whole suites of genes that were associated with the regulation of metabolism and responses to external stimuli. Midge larvae turn proteins on or off in response to stress in their environment — conserving cellular components when they are dehydrated, for example. As they rehydrate, their metabolism picks back up again.
Dr. Teets plans to examine the genetic isolation of midges that live on small islands in the Antarctic, and to compare them with other species of midges in South America.
By studying the environmental stressors affecting the midge, and the strategies it uses to tolerate them, Dr. Elnitsky said, “we may better understand how all cells, including our own, may be impacted and respond.”
Earlier reporting on Antarctica