“They do their best to approximate a sphere,” Loren Buck explained as he removed the ground squirrel from its lab-made hibernaculum. Hibernating Arctic ground squirrels can sustain a core body temperature of just -2.9°C [26.78°F]. “It’s cold… Do you want to touch it?” Buck uncurled the animal carefully. “He knows he’s being handled, it just takes a while for him to ramp up his metabolism to warm. So you can stretch him out.”
ARCTIC GROUND SQUIRRELS: Monday, December 1st 2014, watch the FrontierScientists science special on Arctic ground squirrel research by tuning in to 360 North. Watch over the air from Alaska, or watch online from anywhere in the world by visiting 360North.org at 5am UTC. This 30 minute installment features real scientists and the really cute ground squirrels they work with. Arctic ground squirrels survive body temperatures below freezing yet don’t turn to ice. They use a superpowered circadian clock to stay on schedule despite the unusual timetable of the Arctic sun. They need only a box with bedding to hibernate for an 8 month stretch.
Frontier Scientists, a National Science Foundation funded nonprofit, features scientists’ work through short videos.
Loren Buck, professor of Biological Sciences at the University of Alaska Anchorage, researches Arctic ground squirrels and the animals’ physiology. Arctic ground squirrels are well-adapted to their extreme and variable environment.
He’s looking into the ground squirrels’ clock function. Something in the Arctic ground squirrel’s brain lets them schedule annual and even daily events. For one thing, the animals hibernate through the winter and then awake without apparent cues, calendars or alarm clocks.
“Soil temperatures are constant. They are buried underground under a meter of soil and under snow. It’s dark, it’s continuously cold, there’s no cue for them to be sensitive to, yet these animals all come to high body temperature and emerge to the surface within a very narrow window of time. So what is happening with the clock? Is it the clock that is telling them what time of the year it is when they’ve been sequestered in their burrows?” ~ Loren Buck
For another, during the summertime Arctic ground squirrels leave their burrows to forage for food around 7am and return to their burrows around 7pm. That doesn’t seem strange until you remember that in the Arctic summer, the sun never sets. If it’s light out at midnight, why do the animals get up and go underground at the same time every day?
“What that tells us is: their circadian clock, their master oscillator in the brain is guiding their daily rhythms, and there’s something in the environment that is cueing or entraining that clock. Biological clocks are not perfect, they run about 24 hours. So instead of allowing the clock to drift out of synchrony with geophysical time animals respond to something to correct their biological clock.” ~ Loren Buck
“The strongest resetter is the light dark signal. … But what happens when the sun is above the horizon for 24 hours a day and for weeks and even months? How do animals maintain their rhythmicity?” ~ Loren Buck
The scientists hypothesize that the ground squirrels are responding to the quality and intensity of light instead of its presence or absence. At noon the sun is higher, brighter, warmer and slightly more blue in color. At midnight it’s lower, dimmer, cooler, and slightly more red in color. Perhaps the Arctic ground squirrels can sense those subtle differences and adjust their clocks accordingly.
That makes sense to me. It’s much easier to wrap my mind around than the idea of how the Arctic ground squirrels know how to emerge from their burrows (which have an average temperature of -10°C [14°F] near Toolik Field Station) every spring.
“The clock as we know it resides in the suprachiasmatic nucleus of the hypothalamus, a brain region that is responsible for keeping time. And we know the basics of how it functions. It’s comprised of a hierarchical loop of protein synthesis and degradation. Proteins are synthesized in one part of the day, shut down their own synthesis and degrade in about 24 hours, and that’s what sets the rhythm. Once the protein is degraded, the process begins again. So you have protein synthesis, then a shut down of protein synthesis, and degradation – we know that this clock is driven by protein synthesis and decay. And we know that when animals are hibernating their core body temperature is dropping below -2 degrees [°C] and the protein synthesis transcription and translation processes are greatly inhibited by low temperature. So, does the clock function in hibernation? If the clock functions in hibernation, how does it do so at low temperature? If it doesn’t function during hibernation, how do animals know when to start or end hibernation? ~ Loren Buck
In order to more closely investigate, Buck collaborates with the Institute of Arctic Biology in Fairbanks. A lab there allows scientists to control things like light quality and intensity, and to monitor the animals’ temperatures, metabolism and vital signs. They’re not difficult house-fellows; the ground squirrels can hibernate happily in small cases provided they have plenty of bedding. While hibernating, they have no need to eat, drink, or defecate.
“With the work that we are doing in Fairbanks, we’re trying to figure out if the clock continues to tic, continues it rhythmic transcription and translation of clock proteins.” ~ Loren Buck
“We hypothesize that in addition to a circadian clock they have a circannual clock, one that’s about a years length in terms of its timing.” ~ Brian Barnes
Brian Barnes is the director of the Institute of Arctic Biology at the University of Alaska Fairbanks, and also a Biology and Wildlife Department professor. The University of Alaska Fairbanks lab might house upwards of 200 Arctic ground squirrels. (There’s also a lab which can house over-wintering bears, but that’s another story.) Gaining an understanding of Arctic ground squirrel clock function, both circadian and circannual, will one day help us treat a wide range of human diseases and pathologies.
Waking up to go to sleep
“This guy, he’ll warm up, stay at a high temperature for about 12 hours then go back down into torpor for the next 20 days,” Buck explained as he returned the Arctic ground squirrel he’d held to the hibernation room.
“We try to really limit the amount of exposure that we have. Because every time we go in and out of there we could be bothering their hibernation. And if indeed that is what you are studying, that is not a good thing. So we monitor body temperature remotely. These animals are implanted with a transmitter which sends out a signal that is proportional to their body temperature. The signal is received by a receiver plate, goes to a computer, and we can watch real-time changes moment to moment in body temperature and ensure that these animals are healthy based on their body regulation.” ~ Loren Buck
On of the things they’ve learned is that the squirrels must rouse themselves out of hibernation torpor every few weeks. Barnes describes: the ground squirrels’ highly effective fat-like brown adipose tissue warms up their heart and lungs, and they begin to shiver. That heats their bodies up; they go from frozen to 37-36°C (37°C = 98.6°F, the same average body temperature as humans) and maintain that for about 12 hours.
“This is very curious, why is it they break this state of suspended animation and, indeed, invest energy? They burn fat for such a short period. What do they do during that time? Turns out, they don’t leave their burrow. In fact they stay within their nest and actually stay curled in a ball with their tail tucked over their head, just as in torpor. What they do is: go to sleep. They enter regular sleep stages of slow-wave and REM sleep, just as they do in the summer, and sleep for 8 or 9 hours. They rearrange their nest for a little bit and then go back into torpor.” ~ Brian Barnes
Barnes outlines the hypothesis: hibernation or torpor is not sustainable for 8 full months because when the brain is turned off, it cannot sleep. Just like humans, Arctic ground squirrels need to sleep or they face the consequences of prolonged sleep deprivation.
“Sleep is something all animals need on a regular basis… even if you are a hibernating Arctic ground squirrel, except you only sleep one day every three weeks.” ~ Brian Barnes
Arctic ground squirrels and a changing climate
“In addition being an Arctic resident they are exposed to some of the most rapid changes in climate on earth today. So they are in a changing climate. You have this animal that has evolved in a very extreme environment, that’s been relatively constant over the last 10,000 years and now that environment is changing radically.” ~ Loren Buck
The Arctic is warming on average two times faster than the rest of the world. It’s Arctic amplification. The fast-occurring changes can give us hints about what’s to come for the rest of the world in the coming century.
“The calculations are kind of scary: should the permafrost thaw to a meter’s depth or so around the Arctic (of course there is a lot in Russia), it could double the amount of greenhouse gas in the atmosphere from a natural source. And that could have a huge impact. So people are trying to understand this mechanism, trying to understand what will happen with the birds and the animals and the plants that live there.” ~ Brian Barnes
Buck says that with climate change there’s always going to be winners and losers. Some animals adjust well, some do not. He was asked to describe Arctic ground squirrels’ future fates.
“My prediction is that they won’t thrive under climate change scenarios. I don’t think they will go extinct, but this is a species that has been in Northern Alaska and across Northern Canada for tens of thousands of years. They are permafrost specialists, they are supremely adapted to the tundra lifestyle.”
Modern day changes are altering the Arctic tundra, and sometimes in ways you would not expect. The Arctic is likely to face increased precipitation, which means more snow – “an increased prevalence of late season snow events. That’s a challenge for the ground squirrels. Instead of gradual spring snowmelt they are facing heavy spring snowfalls which cover their food supply. Warming temperatures also favor shrubs over smaller tundra plants which live in the squirrels’ favored habitat. Buck foresees change.
“I think they will continue to to be a major player in the Arctic food webs and that ecosystem. But I think their habitat is going to shrink and their numbers are going to be less that what we have typically thought of as the Arctic ground squirrel population of Northern Alaska.” ~ Loren Buck
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
Arctic Ground Squirrel project
- Interviews with quoted scientists, 2013 & 2014