Arctic ground squirrels may not be as flashy as some other inhabitants of the arctic ecosystem. But what they lack in charisma, they make up for with unique adaptations that help them survive and thrive in one of the toughest environments on Earth. One of these adaptations is their ability to maintain a precisely rhythmic internal clock despite the sun remaining above or below the horizon for long periods in the arctic summer and winter.
University of Alaska, Anchorage professor Loren Buck is working with multiple partners based at Toolik Field Station (located just outside of Fairbanks, Alaska) on the physiological ecology of the arctic ground squirrel to better understand the function and mechanism of its biological rhythms, how they maintain such a precision, and how this unique adaptation in the animal world may possibly benefit people.
Buck’s project, Collaborative Research: Persistence, entrainment, and function of circadian rhythms in arctic ground squirrels, is part of a larger joint effort to monitor biological timing and other characteristics of the arctic ground squirrel.
This month, Buck speaks to Field Notes about his project, his ongoing fieldwork at Toolik Field Station, and how people may benefit from his research to unlock the mysteries of the arctic ground squirrel’s biological clock.
Field Notes (FN): What about the arctic ground squirrel piqued your interest when you first began your research?
Loren Buck (LB): Arctic ground squirrels are the northern most hibernators in North America and the most extreme representation of the hibernation phenotype. I had an interest in the Arctic and, as a physiologist, I was interested in various physiological adaptations, including hibernation. If you’re interested in studying an adaptation, it’s often beneficial to look at the most extreme form of that adaptation. I’ve been working with arctic ground squirrels now for almost 25 years at Toolik Field Station. Over the years, I’ve pursued numerous research questions related to the physiology and ecology of the species.
FN: Arctic ground squirrels are an extreme in the natural world, as you briefly touched on. Please tell us more about their unique adaptations and biological rhythms.
LB: The expression of hibernation in the arctic ground squirrel has been shaped by the many, many years of inhabiting a high latitude environment. They are exposed to a very long, cold and dark winter and a very abbreviated season in which they can be active, reproduce, grow and fatten.
Their hibernation is extreme in terms of the duration. Female arctic ground squirrels, for example, will hibernate for 270 days during which time they don’t eat or drink. The depth of hibernation is also unique. When they enter torpor, they drop their metabolic rate about 98 percent and allow their body temperature to cool. They continue cooling until they reach about -2.9 degrees Celsius. They will regulate at that extreme low body temperature over a 20 or 25-day bout of torpor, after which they warm to a high body temperature for 12-15 hours and then enter another bout of torpor.
The arctic ground squirrel is the only hibernator known to regulate its body temperature below the ice nucleation point of their tissues. This means that the arctic ground squirrel can freeze at that temperature—they don’t produce antifreeze proteins—and thus are in a metastable state while super cooled.
FN: What do you hope to learn about the circadian rhythms of the arctic ground squirrel?
LB: Right now the dogma is that polar vertebrates go arrhythmic across the polar day and the polar night. This means that instead of displaying regular bouts of sleep and activity when the sun is either above or below the horizon for many days, these animals will go arrhythmic and sleep for two or three hours, become active and then sleep again.
However, we found that arctic ground squirrels remain precisely rhythmic, meaning that they go to sleep every night at the same time and they come above ground in the morning at the same time throughout the polar day. The question is—how do they do this? We know that the most potent time-giver for vertebrates is the sun. And if the light environment does not change from May until August every year, how do these squirrels know what time of day it is?
The second question is why do the arctic ground squirrels relegate themselves to being active for 12 hours a day and inactive for 12 hours when the sun is above the horizon? Why not take advantage of this wealth of light and foraging opportunities when summer is so short? Why do they lock themselves in their burrows for 12 hours? So one of our questions is mechanistic—how do they do this, and the second question is more an ecological and behavioral question.
FN: How are you studying the arctic ground squirrels and their circadian rhythms during the 2014 field season?
LB: Our hypothesis is that remaining rhythmic defers some advantage to the ground squirrel, or else that adaptation would have been lost. What we are doing this summer is taking a group of ground squirrels from the field and briefly holding them in captivity at Toolik Field Station. We subdivide that initial group in to a control group and an experimental group. These animals are implanted with data loggers so we can record their body temperatures, which will tell us what phase of the circadian day they are in.
The experimental group will be phase shifted. By using electronic lights and holding them in captivity for a couple of weeks, the animals are shifted 12 hours out of synch with geophysical time. The other group is maintained on a regular 12 hours of light, 12 hours of dark coinciding with geophysical time. Then both groups of animals will be released on the tundra and tracked for the next three or four weeks.
What we’ll look at is if there’s something in the environment that these animals can cue into as evidenced by the experimental group snapping back into synchrony with geophysical time and, if they do, then at what rate? Then we’ll also look at if there’s a metabolic or survival cost to the animals for being out of synch with the environment.
FN: What can this research tell us about our own biological clocks?
LB: Biological clocks are ubiquitous in nature. We too have biological clocks and when they are not functioning appropriately, there’s a high tendency for any number of disease states to manifest—everything from acne to Alzheimer’s. So if we can understand these animal models and how different clocks function in these extreme environments, we may be able to hijack some of that machinery or information in to treatments of disease states that are relevant to people.
For more information on Loren Buck and his research on arctic ground squirrels, visit: http://www.uaa.alaska.edu/biological-sciences/faculty-and-staff/buck.cfm. --Alicia Clarke
Photos and captions
AGS1.jpg: The arctic ground squirrel. These little guys have the unique ability to maintain a precisely rhythmic internal clock despite the sun remaining above or below the horizon for long periods in the arctic summer and winter. Credit: Alicia Gillean
AGS2.jpg: Catching arctic ground squirrels keeps Loren Buck’s Team Squirrel busy much of the summer, but there’s always time for a bit of fun! Here Kate Wilsterman (left) and Jeannette Moore (right) pose for a quick photo before leaving the laboratory at Toolik Field Station to head to Atigun (about 20 miles south of Toolik Field Station) to catch ground squirrels. Credit: Alicia Gillean
AGS4.jpg: Cory Williams (post-doc and co-PI, left), Loren Buck (Lead PI, center) and Kate Wilsterman (NSF Research Experiences for Undergraduates student, right) outfitting a squirrel with a light logger in the field at Atigun. Credit: Alicia Gillean
AGS5.jpg: An arctic ground squirrel burrow in summer near Toolik Field Station. Credit: Alicia Gillean