It’s the ultimate deep freeze: Wood frogs in Alaska have set a record for cold endurance, staying as frozen as your microwave dinner for nearly seven months, a new study says.
Scientists at the University of Alaska Fairbanks discovered that the amphibians survived all those months being chilled to an average temperature of 6°F (-14.6°C), including temperatures as low as 0°F (-18°C).A wood frog (Rana sylvatica) from Anchorage, Alaska. Photograph by Carl Battreall/Nature Picture Library/Corbis
“No other vertebrate has ever shown this duration of freeze tolerance,” said biologist Don Larson, lead author on a study published recently in the Journal of Experimental Biology.
It’s a remarkable feat. Studies of wood frogs in laboratories had led scientists to believe they couldn’t survive such temperatures for more than a couple of months at most.
Larson already knew from laboratory frogs that the animals pack their cells with glucose, a sugar, to stabilize their cells and prevent water loss. But after sampling the tissue of 18 wild wood frogs overwintering in shallow depressions near their spring breeding ponds, he realized that they were even better at this process, known as cryoprotection.
When compared with frozen lab frogs, the wild frogs had glucose concentrations that were 13 times as high in muscle tissue, 10 times as high in heart tissue, and 3.3 times as high in liver tissue.
Larson believes the frogs accomplish this glucose spike through a freeze-thaw process not seen in laboratories. In the wild, temperatures shift, so hibernating frogs will begin to thaw out, then freeze again as night falls—which ups their stores of glucose. (See “Antifreeze-Like Blood Lets Frogs Freeze and Thaw With Winter’s Whims.”)
In fact, the frogs are so efficient at regulating their freeze-thaw cycles, Larson said, that “they’re actually spending more time frozen than a lot of food is capable of staying safe to eat.”
Among vertebrates, the wood frog may be the most cold tolerant. But in the broader animal kingdom, others give the frog a run for its money when it comes to making it through a cold winter’s night—or a hot summer’s day.
Red Flat Bark Beetle (Cucujus clavipes puniceus)
This North American beetle has a broad range that extends from North Carolina to the Arctic Circle.
Accordingly, the beetle has developed a serious ability to avoid freezing. Individuals can drop to temperatures as low as -72°F (-58°C), and their larvae can endure even more remarkable lows without freezing—around -148°F (-100°C).
To achieve this, the bark beetle accumulates antifreeze proteins and glycerol—a sugary alcohol that’s the basis for many antifreeze products—in its tissues while reducing its metabolism and entering a state of dehydration in order to avoid a frozen, rock-solid state.
Dehydration increases concentrations of the antifreeze proteins and glycerol, while simultaneously decreasing the amount of water that’s available to freeze.
Combined, these factors allow the beetle to maintain an on-and-off active lifestyle in some of the harshest conditions on the planet. (See: “Animal ‘Zombies’: Nature’s ‘Walking Dead’ in Pictures.”)
Pompeii Worm (Alvinella pompejana)
Named for the hydrothermal vents near where it lives, this underwater critter thrives in temperatures that are almost hot enough to boil water.
Scientists believe the worm is able to tolerate such scorching temperatures because of a mutually beneficial relationship with a mysterious fuzzy bacterium. The bacterium appears to insulate the worm, protecting it from the heavy metals churned out by the seafloor’s vents.
Sahara Desert Ant (Cataglyphis bicolor)
The Pompeii worm may rule the ocean’s depths, but the Sahara desert ant is one tough land dweller. The insect forages even when its body temperature is above 122°F (50°C), making it one of the most heat-tolerant species to walk the Earth.
Its long legs keep its body off the hot desert sand, where temperatures can be ten degrees warmer.
Most intriguing, though, is its hunting strategy. The Sahara desert ant is the only ant that continues to look for food once temperatures rise above 113°F (45°C). Under a broiling sun, they scavenge the corpses of other ants and insects that couldn’t handle the heat.
Water Bear or Tardigrade (Hypsibius dujardini)
As tough (and cannibalistic) as the Sahara desert ant may sound, nothing beats the water bear, also known as a tardigrade or moss piglet. It’s the king of extreme temperatures, capable of surviving lows near absolute zero (-459°F; -273°C) and highs of more than 302°F (150°C).
Found in hot springs, nestled under solid ice, and at the top of the Himalaya, these tiny invertebrates can even survive outer space.
In 2007 Swedish researcher K. Ingemar Jönsson rocketed a few tardigrades into space using the FOTON-M3 spacecraft. Even after being exposed to the vacuum and cosmic rays of space, they lived.
Now that’s tolerance of astronomical proportions.
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