April showers usually bring May flowers, but in Alaska, spring’s rainy days will cause a different kind of life to emerge from the earth: Zombies. But these undead are more interested in mosquitos than human body parts. For the past seven months, Alaska food frogs have been buried in mud and leaf litter, void of all appearance of life. But when temperatures consistently stay above freezing, these zombies are ready to emerge from their frozen tombs. No kidding.
The Alaska wood frog, Rana sylvatica, is an amphibian that freezes solid during the winter months, only to miraculously thaw and come alive in the spring. Researchers from the University of Alaska have shown that this tiny frog the size of your hand can remain in this frozen state for seven months with temperatures dropping to -40°F. We can’t do that, no animal can. It’s crazy.In cold climates, warm-blooded animals adapt to the weather by migrating to warmer places (like geese flying south), or find a shelter where they curl up and stay warm (like bears in a den). Some fish will even build up sugars called glycogen in their bodies to lower their freezing point all winter, but they never freeze solid. If they did freeze the damage would be deadly. But the little, slimy wood frog possesses a biological trick.
Before the snow falls each winter, the frogs dig into the dirt and cover themselves with leaf litter, creating a hibernacula (a place they will spend the winter), then, they wait. A system of cryoprotection, or “freeze protection,” is then triggered and fueled by the alternating freeze/thaw cycle of autumn as our environment transitions to winter. The frogs thaw during the day and refreeze overnight; their bodies releasing glucose, a sugar. Over time this sugar builds up, acting like anti-freeze in a car, preventing dehydration and frost damage (you know, like when you leave a steak in the freezer too long). The amount of sugar stored in a single wood frog is similar to the amount of sugar found in the blood of a human child (you!). If you licked a frozen frog, it would likely taste as sugary as a soda. Eventually, the wood frog’s breathing and heart rate comes to a complete stop, and brains become void of activity. The frog is as dead as dead can be, but yet at the most basic cellular level, a tiny bit of metabolic activity (chemical reactions) remains.
Months later, when days grow longer and warmer, the wood frog stirs, slowly at first. Scientists are still baffled how the frog thaws out heart and liver before anything else, allowing them to convert much of the stored glucose in their bodies into energy, and then release the excess (yeah, they go to the bathroom). Within hours of this miraculous warm-up, they gather at the nearest pond to feast and begin reproducing, and this is when we are most likely to see hear them. The call of a wood frog sounds a bit like a duck; “quock-quock-quock.”
In about 45 days, the eggs they lay in ponds will metamorphose (change shape as they grow) into adults and begin their feast on bugs, insects and small invertebrates (little tiny creatures found in the water and nearby shoreline) before repeating the process of burying, freezing and “dying.”It’s fun to explore Alaska’s ponds and lakes, looking for wood frogs. In Anchorage, these little guys have been monitored at over 200 sites around town, including Far North Bicentennial, Kincaid and Earthquake Parks. Mushy, marshy areas are a wood frog’s favorite habitat, so places like Point Woronzof near Ted Stevens Anchorage International Airport and the backside of Potter Marsh are good bets for finding frogs, too.
Scientists still have a lot to learn about the wood frog, and you can help them. All kids are encouraged to become a Citizen Scientist with the Alaska Wood Frog Monitoring Project. This is a fun way to learn more about Alaska amphibians and wetlands while collecting and sharing important data with amphibian researchers.
This is one zombie you’ll be glad to know! ￼
Bryan Bearss is an Anchorage teacher, Iditarod musher, and outdoor education specialist. AKontheGO is thrilled to introduce him as the newest member of the growing “AK Family” of contributors. Look for more Kids Corner contributions by Bryan in the coming months.