The Amazing Science of Hibernation: How Animals Survive the Deep Freeze

Hibernate like an Arctic ground squirrel? Imagine slowing your heart rate to a crawl, dropping your body temperature to near-freezing, and sleeping for months on end. For many animals, hibernation is not just a long nap; it's a survival strategy. Let's delve into the fascinating world of hibernation and explore how certain species endure the harshest conditions.

The Necessity of Hibernation

For many animals, hibernation is a necessity, a survival tactic for making it through the harsh winter months when dwindling food and water reserves threaten survival. Experts used to believe hibernation only occurred in arctic and temperate environments, but they’ve recently discovered animals hibernating even in arid deserts and tropical rainforests.

Extreme Examples of Hibernation

• Arctic Ground Squirrel: This remarkable creature, native to the North American tundra and northern Russia, burrows beneath the permafrost and enters a state of suspended animation. Its body temperature can plummet to a frigid -2.9 degrees Celsius.
• Black Bear: The female black bear showcases multitasking at its finest, giving birth and lactating while hibernating through the winter.
• Fat-Tailed Dwarf Lemur: This lemur prepares for its long dormancy by gorging on food and storing the majority of its fat reserves in its tail, doubling its body weight. After hibernation, it emerges looking as svelte as ever.

The Physiology of Hibernation

As hibernation kicks in, animals experience dramatic physiological changes:

• Heart Rate: Heartbeats usually slow to about 1 to 3% of their original speed. For example, the dwarf lemur's heart rate drops from roughly 180 beats per minute to just around four.
• Breathing: Breathing also declines dramatically, to just one breath every 10 to 21 minutes in the lemur’s case.
• Waste Management: Black bears, like most hibernators, don’t urinate or defecate the entire hibernation season.
• Brain Activity: Scans of hibernating animals reveal that their brain activity has just about flat-lined.

Hibernating animals appear to stay alive by having just enough blood and oxygen moving around their bodies.

Torpor and Interbout Arousals

Hibernation isn’t a long winter’s nap. As far as researchers know, in lemurs and ground squirrels anyway, the animals aren’t even sleeping for most of it. Hibernation is actually made up of regular bouts of reduced metabolic rate and body temperature known as torpor. Animals can be in torpor for a few days to five weeks, after which they resume normal metabolic rate and body temperature for about 24 hours before going back into torpor again. The phenomenon is known as an interbout arousal, and why it occurs is still a mystery.

Genetic Control of Hibernation

The behaviors inherent in hibernation, like going five weeks without sleep or dropping to near-freezing body temperatures, would be potentially fatal to non-hibernating species. To find out how hibernators are able to do this, researchers turned their attention to those animal’s genomes.

So far, they’ve discovered that hibernation is controlled by genes that turn off and on in unique patterns throughout the year, fine-tuning the hibernator’s physiology and behavior. For example, ground squirrel, bear and dwarf lemur studies have revealed that these animals are able to turn on the genes that control fat metabolism precisely when they need to use their fat stores as fuel to survive long periods of fasting.

And the genes in question are present in all mammals, which means that researchers could study hibernating mammals to see how their unique control of physiology might help humans.

The Future of Hibernation Research

Understanding how hibernators deal with reduced blood flow could lead to better treatments for protecting the brain during a stroke. Figuring out how these animals avoid muscle deterioration might improve the lives of bedridden patients. And studying how hibernating animals control their weight with ease could illuminate the relationship between metabolism and weight gain in humans.

And yes, more research in this area might someday make human hibernation a real possibility. Imagine our surprise if the key to intergalactic travel turns out to be ground squirrels, black bears, and dwarf lemurs.