Arctic Ground Squirrel (Urocitellus parryii): The Arctic ground squirrel survives winter hibernation with core body temperatures dropping below 0°C—down to -2.9°C—without freezing. It achieves this through supercooling and periodic arousal, where it briefly warms up every few weeks, possibly to repair cellular damage. Living above the Arctic Circle, it prepares by storing fat and burrowing deep below the permafrost. Its blood contains antifreeze-like proteins that inhibit ice formation. During hibernation, its heart rate drops from 200 to just 1 beat per minute. In summer, it remains active in cold tundra, relying on insulation and social warmth. This rodent’s extreme cold tolerance provides insights into medical applications like organ preservation.
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