Scientists have discovered that snow flies, small wingless insects, produce antifreeze proteins and generate their own body heat to remain active in subfreezing temperatures as low as -6 degrees Celsius. Researchers at Northwestern University sequenced the insects' genome for the first time, revealing unusual genes and reduced sensitivity to cold pain. The findings, published March 24 in Current Biology, offer insights into adaptations for extreme cold.
Snow flies crawl across snowy surfaces in search of mates and to lay eggs, thriving in conditions that immobilize most insects. A study led by Marco Gallio, a professor of neurobiology at Northwestern University's Weinberg College of Arts and Sciences, uncovered multiple survival mechanisms in the species Chionea alexandriana. Co-led by Marcus Stensmyr of Lund University in Sweden, the research team found that these insects produce antifreeze proteins structurally similar to those in Arctic fish, which bind to ice crystals and prevent cellular damage from freezing. They also identified genes associated with mitochondrial thermogenesis, enabling the flies to generate heat akin to brown fat in mammals like polar bears. Experiments confirmed this: modified fruit flies expressing snow fly proteins survived freezing better, and the insects themselves maintained internal temperatures a few degrees warmer than ambient cold without shivering. Gallio noted, 'Snow flies aren't just tolerating the cold, they have multiple ways to counteract it.' The team sequenced the snow fly genome, revealing many novel genes not found in databases. 'Initially, I thought we must have sequenced some alien species,' Gallio said. Additionally, a key sensory protein for detecting cold irritants is 30 times less sensitive in snow flies than in mosquitoes or fruit flies, allowing them to endure extreme stress. Stensmyr added, 'Snow flies instead likely produce heat at the cellular level, more similar to how mammals and even some plants generate heat.' These adaptations explain why snow flies prefer cold, snowy conditions and retreat when it warms. The work, supported by groups including the National Institutes of Health and National Science Foundation, could inform strategies to protect cells and tissues from cold damage.
