February 13, 2007
How do animals living in the continuous light of the Arctic summer know when to sleep and when to be active? Do they maintain a 24-hour cycle of rest and activity, or does living in continuous light alter their circadian rhythm? Answering these questions may improve our understanding of biological clocks—the internal, genetically programmed cycle of rest and activity that affects the behavior, metabolism, and physiology of all animals, including humans. A better understanding may also help solve problems—such as shift-work fatigue, jet lag and even seasonal affective disorder—that are associated with disruptions of biological clocks.
One scientist who has spent a lifetime pursuing these questions and finding answers that have helped build the field of biological clock research is G. Edgar Folk, PhD, emeritus professor of molecular physiology and biophysics at the University of Iowa Roy J. and Lucille A. Carver College of Medicine.
Working at Folk’s permanent Arctic field lab at Barrow, Alaska, the research team studied two types of Arctic rodent: nocturnal porcupines and day-living ground squirrels.
Heart rates—a good measure of metabolism and activity—from four porcupines and direct observation of nine squirrels’ activity showed that both creatures retained a 24-hour rhythm of behavior during the 24-hour daylight of the Arctic summer, just as they would if they were living under a normal day/night situation. The study results are published in the December 2006 issue of Biological Rhythm Research.
“We postulate that the animals are conscious of where the sun is in the sky and that the nearness of the sun to the horizon could be a clue to animals, and even plants, to keep on a 24-hour schedule,” Folk said. “Our work shows that clocks are important, and for me it means that you get surprises—I thought that we would see drift in the times the animals slept, but we didn’t. The broad implication is that, when possible, animals like humans, like to have regularity.”
Folk found that several other scientific teams have also proposed the same theory.