Snow flies may look like ordinary insects, but their survival strategies are atypical.
In a new study, Northwestern University scientists investigated how these tiny wingless insects, which move across snowy surfaces to find mates and lay eggs, stay alive in frigid environments. They discovered that snow flies rely on a surprising combination of biological tools. The insect generates its own body heat, like mammals, and can produce antifreeze proteins similar to those found in arctic fish.
Although most insects cannot survive below freezing temperatures, snow flies can remain active at temperatures as low as -6 degrees Celsius (21.2 degrees Fahrenheit).
These discoveries provide new insights into how life adapts to extreme environments. It could also help researchers develop new ways to protect cells, tissues and materials from cold-induced damage.
The study was published in the journal March 24th. current biology.
“Insects are cold-blooded animals, so they depend on the outside temperature,” said study leader Marco Gallio of Northwestern University. “However, they have an amazing ability to adapt to extreme conditions. When it gets cold, a common strategy is to find shelter and go dormant until conditions improve. But rather than slowing down, snow flies actually stay in the freezing cold. They prefer snowy environments and hide when the snow melts and it gets warmer. They’re really pushing the boundaries of what’s possible. Now we’ve discovered that snowflies not only survive the cold, they have multiple ways to combat it.”
Gallio studies how temperature shapes biology and is the Soletta and Henry Shapiro Research Professor of Molecular Biology and professor of neurobiology in Northwestern’s Weinberg College of Arts and Sciences. He co-led the study with Markus Stensmil, a professor of biology at Lund University in Sweden. Other Northwestern contributors include William Cass of the McCormick School of Engineering and Alessia Parra of Weinberg. Gallio and Kath are also affiliated with the NSF-Simons National Institute for Theory and Mathematics in Biology (NITMB).
Abnormal genes and antifreeze proteins
To understand how snow flies survive such harsh conditions, researchers first examined the snow flies’ genetic makeup. Gallio and his team sequenced the snow fly genome for the first time and compared it to related insects that are less adapted to cold environments. They also analyzed the RNA to determine which genes are actively used to survive below freezing temperatures. These complex comparisons were performed by Dr. Richard Suchendra. A student who works with Cass.
The results were unexpected.
“Many of the genes were not found in any database,” Gallio said. “At first, we thought we must have sequenced some kind of foreign species. It’s very rare that the active genes that make proteins don’t match.”
Further investigation revealed that these unusual genes produce antifreeze proteins. Similar to those found in Arctic fish, these proteins attach to ice crystals and prevent ice from growing. This process protects the cells from damage during freezing.
“Surprisingly, some of the antifreeze proteins we discovered are actually structurally related to those in Arctic fish,” Gallio said. “It suggests that evolution has arrived at the same solutions to common problems.”
Heat production helps keep flies active
The research team also identified genes associated with cellular processes involved in energy use and heat production. This suggested another unexpected ability. Snow flies not only withstand freezing, but also generate their own heat.
“We discovered a gene associated with mitochondrial thermogenesis in brown adipose tissue in large animals,” Gallio said. “Many animals, such as marmots and polar bears, have brown fat to produce heat. When they go into hibernation, they burn this stored fat to produce heat, rather than producing chemical energy. So in a sense, snow flies are using a combination of strategies used by polar bears and arctic fish.”
Blocks ice and creates warmth
To test how antifreeze proteins work, Dr. Matthew Kapek and students in Gallio’s lab modified a fruit fly to produce one of the snow fly proteins. They then exposed them to subzero temperatures in a laboratory freezer. The modified flies survived at a much higher rate than normal fruit flies, confirming that the protein acts as a barrier to prevent ice from spreading.
In another experiment, the researchers tested whether snow flies actually generate heat. The insect’s internal temperature was measured while the ambient temperature was gradually lowered to below freezing. During this process, the snow flies remained slightly warmer by several degrees Celsius than expected compared to other insects.
“Other insects, such as bees and moths, shiver to increase their body temperature,” Stensmar says. “But we found no evidence of shivering. Snow flies likely produce heat at the cellular level, more similar to how mammals and some plants produce heat.”
Even small increases in temperature are critical to survival in such extreme conditions. This brief period of warmth can give snowflies enough time to find shelter and avoid freezing when temperatures plummet.
Decreased sensitivity to cold-induced pain
Snow flies also appear to be insensitive to the painful effects of extreme cold. Most people experience sharp pain when they touch ice or cold metal. This sensation is caused by reactive molecules in your cells that signal your body to avoid harm. In snow flies, this response is significantly reduced.
Gallio and his team found that the reactivity of key sensory proteins involved in detecting noxious stimuli is much lower in snow flies than in other insects. As a result, these insects are able to withstand higher levels of cold-related stress and continue to function under conditions that would overwhelm most species.
“We found that certain stimulus receptors are 30 times less sensitive in flies than in mosquitoes and fruit flies,” Gallio said. “So they can cope with the high levels of harmful irritants produced by cold exposure.”
Future research on survival in extreme cold regions
Next, the researchers plan to investigate in more detail how snow flies generate heat at the cellular level and identify the full range of antifreeze proteins that snow flies produce. The study could reveal whether other organisms employ similar strategies to survive in extremely cold environments.
The study, “Adjustment of molecular and physiological adaptations enables subfreezing activity in the snow fly Chionea alexandriana,” will be published in the April 6 issue of the journal. current biology And the cover feature. Research in various laboratories was supported in part by the National Institutes of Health, the Pew Scholars Program, the McKnight Foundation, the Paula M. Trienens Institute for Sustainable Energy, the Crafford Foundation, the National Science Foundation, the Simmons Foundation, and the NITMB. External collaborators included the DNAzoo project as well as Rice University and Baylor College of Medicine faculty members Olga Dudchenko and Erez Lieberman-Aden.
