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.”