By Dan Strickland
Originally printed in the The Raven, Volume 36, No 12, published by Algonquin Provincial Parkon September 7, 1996.
Now that […]another busy Algonquin camping season is winding down, we don’t have to look far to see signs of bigger changes to come. The nights are nippy and many maples have already started to turn color. Chipmunks scurry through dead leaves on the forest floor, laying in their winter larders, and basking turtles are soaking up the sun’s last bit of warmth around a thousand beaver ponds.
It is obvious that the animals of Algonquin Park must prepare for the winter that lies ahead and everyone knows that there aren’t a lot of choices. Some creatures escape altogether by migrating south to warmer climates, some grow thicker coats and fatten up, and still others retreat to some sheltered hiding place to hibernate through the bitter Algonquin winter.
Of these limited possibilities, the last is the one that usually appeals to us the most. We all have the simple and unsophisticated, albeit very pleasing, picture of curling up in a nice warm den somewhere for a long and cozy winter snooze. And yet, as attractive as this image may be, it really misses the mark. Overwintering animals may indeed do some serious snoozing but, if we know even half the truth about hibernation, we would find words other than simple, unsophisticated or cozy to describe it.
One of the best examples of what we mean is given by our common Painted Turtles, the ones we see basking in the sun out on logs in places such as Wolf Howl Pond on the Mizzy Lake Trail or along the Madawaska River on the Track and Tower Trail. Soon, when the weather gets really cold, these turtles will disappear from view down to the bottom of their local water body. There, they will hibernate through to next spring, under the ice.
Now, we suspect that most people take this fact more or less for granted, having learned it in childhood. We seldom stop to reflect, however, just what an extraordinary thing it is. After all, here is an air-breathing animal, like us, that one day just goes down to the bottom of its pond and doesn’t take another breath for the next six months! To be sure, hibernating Painted Turtles may be capable of absorbing some oxygen from the surrounding water through their skin. Some frogs can definitely do this and there is some evidence that Painted Turtles can holdout longer and with less stress when they are immersed in oxygen-rich water.Still, the fact remains that Painted Turtles often hibernate right down in the bottom mud where there is no oxygen at all. Also, even when they spend the winter resting actually on, rather than under, the bottom surface, the oxygen under the ice in many ponds often runs out before the end of winter. And, lest there be any remaining doubt on the subject, Painted Turtles in the laboratory have been proven capable of surviving for as long as [five months] while continually submerged in water that contained no dissolved oxygen at all.
Such an amazing feat is obviously far beyond what we can reasonably call simple and seriously challenges our ability to explain it. True, we did omit the important detail that the Painted Turtles which survived the five months without oxygen did so in water that was only 37°F (3°C). This provides at least a partial answer because turtles are cold-blooded, meaning that their body processes are slower at colder temperatures and that they, therefore, have less need for oxygen under those conditions. But there is much more to the ability of hibernating Painted Turtles to get along without oxygen than that. In addition, submerged turtles can somehow slow down their metabolic processes even further, perhaps with special hormones, down to a mere ten percent of what their rate would be in an animal at the same temperature but with access to air.
And even this isn’t the whole story. Perhaps the most important thing of all is that Painted Turtles store food energy, not in the form of fat the way mammals do, but as carbohydrates called “glycogen.” Glycogen can be broken down, thus liberating energy for use by the turtle elsewhere, without consuming oxygen, in a process known as “glycolysis.”
This is the same process that occurs in human muscle cells when we are running fast or otherwise using up energy more quickly then we can bring oxygen to those cells. In both humans and turtles the process results in a build-up of lactic acid, a substance that is poisonous to animals cells. With us, a lactic acid build-up causes extreme pain in our muscles and forces us to stop and pant so as to bring in more oxygen that will clear out the accumulated acid. Hibernating turtles have a much more elegant way around the same problem. They use calcium and magnesium to neutralize their acid build-ups. And where might they get this life-saving calcium and magnesium? You guessed it—from their shells! In other words, a Painted Turtle can hibernate for months without oxygen in part because it carries not just its house, but also its pharmacy, around on its back.
As impressive as the hibernating abilities of adult Painted Turtles may be, however, they are almost nothing compared to those of their babies. Female Painted Turtles lay their eggs in June, after first excavating suitable chambers in gravelly soil, often on south-facing slopes. When all the eggs has been deposited, the females cover over the chamber and leave, letting the sun’s warmth incubate the eggs over the Algonquin summer. They usually hatch in September, but then something peculiar happens. Rather than digging their way out and joining older turtles in nearby water, the hatchling Painted Turtles just stay put. Though hatched, they spend all winter underground and emerge only the following spring. Such behaviour has a few advantages, particularly that of lessening their exposure to predators,but having a nice warm place to spend the winter is not one of them. Two nests whose temperatures were measured one winter here in Algonquin Park, for example, ranged between 18° and 28°F (-10° and -2°C) through January and February in spite of all the insulation provided by the ground itself and a thick layer of snow. All 13 of the baby turtles in these two nests nevertheless survived, even though it was hard to see how they could have avoided freezing solid.
Later experiments were carried out in a lab to see what really might have happened to the baby turtles. When hatchlings were put in a special incubator and the temperature slowly lowered, they went well past the supposed freezing point of turtle blood(31°F or -0.5°C). It was beginning to look as if Painted Turtle hatchlings might have some non-understood ability to defy the normal laws of physics. But then, when their temperatures reached 26.5°F (-4°C), they suddenly froze. Ice quickly formed on their outer skin and over the next several hours words, the ice grew inwards, first cutting off blood circulation to the surface areas of the turtle and eventually shutting it down completely. The hatchlings ended up,to all appearances, frozen solid, with no muscle movement, no heartbeat, no blood flow, no breath, and only the barest remnant of brain activity. And yet,incredible as it may seem, when the baby turtles were thawed out a day later, they all came back to life as if nothing had happened.
This was a truly astonishing result because, as any gardener knows, not to mention anyone who has ever lost a toe or finger to frostbite, the freezing of living tissue is normally a devastating experience. What does the real damage is the formation of ice crystals inside cells. The little slivers of ice pierce delicate membranes and irreparably disrupt the finely-tuned structures and organization essential for a cell to function and live. How then, can hibernating hatchling Painted Turtles freeze solid and then, even weeks later, almost literally rise from the dead?
It turns out that baby Painted Turtles have two very special mechanisms that save them from what would otherwise be certain and very painful death. As its body temperature drops, a hatchling’s liver starts to manufacture special proteins that are then distributed to all the bodily fluids that lie outside cells. These fluids include blood plasma, abdominal fluid and urine. When the turtle’s body temperature reaches the freezing point of these fluids, the special proteins,by now all in place, actually serve as starting points for the formation of ice crystals. This sounds disastrous but what is happening is that the crystals are all forming in a controlled manner outside the turtle’s cells. In particular,they form in such a way that each one of them remains very small, rather than growing into a large and potentially very damaging ice dagger. Also, as more and more of the fluids outside the cells freeze, much of the water inside nearby cells tends to be drawn outside and be added to the growing mass of crystals that is forming safely outside the delicate cells. At the same time,the cells have set in motion the production of what amounts to anti-freeze—sugar compounds like glycerol and glucose that lower the freezing point of the water still inside the cell walls. The final result is that only 53 percent of a hatchlings body water is actually frozen and all of that amount is outside the cells and in the form of very tiny ice crystals that can’t do very much damage.
This is how hatchling Painted Turtles hibernating through their first winter while still inside their nest chamber, escape death even though they are frozen solid. After that first winter, baby Painted Turtles no longer have the ability to make the special proteins that serve to control and confine the formation of ice crystals to the spaces outside their body cells and they accordingly lose their ability to withstand freezing. But by then, of course, it doesn’t matter. For the rest of their lives they will hibernate in the water below the ice at balmy, above freezing temperatures of 35° to 49F° (2° to 5°C). Under those conditions, they don’t have to worry about freezing to death and, as we have already seen, all they will have to do is hold their breaths and go without oxygen for six months.
By now we think you will agree with us that words like “simple”, “unsophisticated” and “cozy” are a little misplaced when it comes to describing hibernation. Certainly, for the Painted Turtles we see these days soaking up the last September sunshine along the Mizz Lake Trail and a thousand other places in Algonquin, they will soon be doing a lot more than merely settling in for a long winter snooze.
Wouldn’t it be more fair to say that they are about to settle in for a long winter miracle.
Click here to access the article as originally published.
Photo by Sabrina Serato
Last modified: March 5, 2019