Cold Blooded Doesn’t Mean a Hert of Ice

Design is a funny word

Cold Blooded Doesn't Mean

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A heart of Ice

Wood frog thawed

It's October in Alaska (USA), the weather is getting colder and you can only find shelter in a few piles of leaf litter in the subnivean zone (check out the Arctic cutaway below). Your body begins to slow down, your breathing becomes slower and slower. Just as you find the perfect spot to crawl into, ice begins to form on your skin, freezing your body into a cryo state where all bodily functions seem to completely stop functioning. Winter passes, more snow falls covering you even deeper in the snow. At one point your body even dips down to -12°C. Nothing on this earth could survive this kind of wintery torcher. But then The Snow begins to melt, the temperature rises, and the sun shines just enough to thaw you out, spontaneously sparking your frozen heart to start beating once more. Your limbs were not even affected by the sub-zero temperatures and you just get up and walk away, like it's your annual wintery dance with death.

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moose icon

This is what we see, It's the desolate surface of the Arctic ecosystem

frog icon

Literally meaning "Under the Snow", this is where all of the smaller animals go to survive the harsh winter conditions of the Arctic. 

Arctic Cutaway, Click  and for more details

Wait...WHAT?

What kind of Black magic, Twilight Zone crazy Sci-Fi made up crap is this?  Is something, you are probably thinking right now. but, if you were a Wood Frog (Lithobates sylvaticus) it is just another year gone by.  With every consecutive cycle of "The Day after tomorrow" conditions, the wood frog increases the amount of antifreeze (or if you want to be fancy "Cryptoprtectant") which in the case is glucose. Compared to frogs taken from the more southern range (around Virginia, USA) Wood frogs in Alaska had 13 fold higher glucose levels in their muscle tissues, 10 fold higher glucose levels in their heart and 3.3 fold higher glucose levels in their livers. With these huge amounts of glucose running through their body tissues the tiny 2.5 in (63.5 mm) frogs are subjected to temperatures as low as-14.6±2.8°C, with a 100% survival rate. (4)

So, Wait if glucose is just sugar, can you just eat a ton of powdered doughnuts in the apocalypse that is "The Day After Tomorrow" icy doomsday film of the early 2000s? I mean, you could try, it would not do you any good.

When temperatures begin to edge past freezing, proteins in their blood, called nucleating proteins start going to work, seeding ice to form faster in the bloodstream and extracellular spaces, outside of the cells. With Ice outside of the cells only, Water begins to be drawn outside of the frog cells, essentially drying them out from the inside out. (4)

While the Frog is beginning filled with ice, its liver begins to make copious amounts of glucose. This glucose is packed into its cells before they dry out completely, propping them up from the inside, so lack of water does not collapse the frog's cells, which would destroy them instantly. With the cells popped up with sugar (glucose) and Ice forming through its veins, the wood frog begins to stops all metabolic and brain function. (4)

Unfrozen Wood Frog Frozen wood frog
By DDauri Daniel D'Auria - Own work, CC BY-SA 3.0, Link

It is crazy to think, but at this point, roughly 192 days pass with zero motion, zero metabolism, zero brain function, Zero Everything! Then, the sun begins to shine just a little bit brighter, the days become just a little bit longer, the ice inside of wood frog begins to melt. After about 20 minutes it is completely thawed out, then after another 20-30 minutes, its heart begins to spontaneously beat again. After the heart starts blood begins to flow, then breathing, and after a while, hopping around like nothing happen.

To be fair, there are a few other elements to this black magic. Urea also builds up and is utilised as a cryoprotectant with metabolism suppression double duty.  Glycolipids build up in the internal organs to aid as antifreeze, but oddly enough, the frog's skin does not get extra protection from freezing in this way.

For us humans, When we get frostbite, our cells dry out just like the tiny wood frog, but we do not have an excessive amount of glucose inside our cells. Without this added glucose, our cells collapse and there is no turning back.

How these frozen frogs are helping preserve human Organs

I think we will all agree that human organs do not last very long outside of the body for very long. A human heart can last up to 6 hours, max; fora liver, it's 12 hours.  Research into the cryoprotectants utilized by wood frogs is currently in its infancy as reported by WVXU.org, but with the possibilities to theoretically preserve organs indefinitely, studying wild adaptations like this, have great potential to save countless lives in the future. 

The invincable Alligator

If you want to look into the past about 80 million years, you do not have to go any further than the American alligator (Alligator mississippiensis) or any of the other equally terrifying crocodilians for that matter. When the earth was smacked by a massive comet or asteroid about 66 million years ago during the K-T extinction, there were very few large (over 55lbs(25kgs)) animals that survived. Leatherback Sea Turtles (Dermochelys coriacea) came out survivors and so did Brachychampsa, the ancestor of every alligator, crocodile, and caiman alive today. 

Over the millennia, not all descendants of Brachychampas adapted to the frigid temperatures quite like the American alligator. The American crocodile (Crocodylus acutus), for example, was observed in the winter of 2010, basking in the sun as it does to warm up its core body temperature, the only problem is that this particular winter brought temperatures below 40°F for a record 6 days in a row for the Miami Area¹.  Basking in the open air at these temperatures lowered the American crocodiles' temperature to a lethal state, killing many of them almost instantly.  Normally, basking in the sun is a good idea for any ectotherm (cold-blooded) animal, such as these large reptiles, but in this case, the open air was actually colder than the bodies of water in the area; Cue the American Alligator. 

Brachychampas v. American Alligator
Brachychampsa (80 MYA) American Alligator (Present day)

Once temperatures begin to dip. American alligators retreat to the water and mud pits that they create, rather than continue to bask in the sun like the American Crocodile. Since water can retain more heat than air, this behaviour strategy keeps its core body temperature higher than basking in the sun in this environment. In some cases, the right microenvironment might see the perfect amount of sunlight, shielding from wind, and decaying vegetation to increase their body temperature high enough to be considered "active"².  So, Just because it's a cold day in alligator country, don't rule out the possibility of one of these massive reptiles jumping out at you. 

 

This key behaviour difference between American Alligators and American Crocodiles is, in fact, a very significant reason why alligators have dominated the American south-east and the Crocodile has not gone beyond the Gulf of Mexico coastline. Though there is one other key factor allowing the American Alligator to dominate higher latitudes, and that's brumation. 

Having the ability to continue to maintain life at temperatures near freezing is a big advantage. When the cold weather triggers an alligator to retreat into the water, even if the top layer freezes over, the underlying liquid water becomes insulated from the outside weather conditions.  Of course, not all alligators will survive, the young and weak will most likely not see the springtime and if their body does begin to freeze over, they do not have freeze protection like the Alaskan wood frog. Though, over the past 80 million years this ancient monster has more than proved it has what it takes to be invincible.

An adaptive trick that helps these reptiles survive in winter weather

What is Brumation?

Flip to find out

Deffinition

A state or condition of sluggishness, inactivity, or torpor exhibited by reptiles (such as snakes or lizards) during winter or extended periods of low temperature.

-Webster's dictionary

These are but only two examples of the wildly amazing wildlife around us every day.  We encourage you to download the Search Wildly application and explore the satisfaction of marking your wildlife encounters, setting up encounter groups, being surprised by new upgrades and abilities (even more if you are a pro user for just $1-$2) and just being part of an amazing grassroots wildlife exploration social group.

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References
  1. NATIONAL WEATHER SERVICE, WEATHER FORECAST OFFICE, NOAA. “2010 South Florida Weather Year in Review.” Weather.gov, 2010, www.weather.gov/media/mfl/news/2010WxSummary.pdf.
  2. Thomas, Bob. “Loyola University New Orleans.” Where Do Alligators Go In Winter? | Center for Environmental Communication | Loyola University New Orleans, 2010, www.loyno.edu/lucec/natural-history-writings/where-do-alligators-go-winter.
  3. Hagan, John M., et al. “Behavioral Response of the American Alligator to Freezing Weather.” Journal of Herpetology, vol. 17, no. 4, 1983, p. 402., doi:10.2307/1563593.
  4. Larson, D. J., et al. “Wood Frog Adaptations to Overwintering in Alaska: New Limits to Freezing Tolerance.” Journal of Experimental Biology, vol. 217, no. 12, 2014, pp. 2193–2200., doi:10.1242/jeb.101931.

About Author

Evan Ogden

Writer for and owner of Search Wildly, Evan has devoted himself to bringing the wild into focus through accounts of his wildlife interactions and development of the search Wildy Application (on IOS and Android).

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