WSU Study Finds Grizzly Bears’ Internal Clocks Keep Ticking During Hibernation
WASHINGTON — A genetic study led by researchers at Washington State University (WSU) has revealed that the internal clocks of grizzly bears continue to function during hibernation. This study emphasizes the significant role of circadian rhythms in the metabolism of various organisms, including humans.
The circadian rhythm is a 24-hour cycle that is part of the body’s internal clock and influences physical, mental, and behavioral changes. It responds primarily to sunlight and darkness and affects most living organisms.
The WSU study confirmed that bears’ energy production still follows a daily pattern even during hibernation, despite hibernating for several months without eating. Researchers also found that the amplitude of the energy production was reduced during hibernation, meaning that the range of highs and lows was diminished.
Additionally, researchers noted that the peak of energy production occurred later in the day during hibernation than during the active season, but the daily fluctuation persisted.
“This underscores the importance of the circadian rhythms themselves – that they give organisms the flexibility to still function in a state as extreme as a hibernating bear,” said Heiko Jansen, a professor in WSU’s integrative physiology and neuroscience department and the senior author of the study published in the Journal of Comparative Physiology B.
The research also highlighted the ties between circadian rhythms and metabolic health. Major disruptions to circadian patterns have been linked to metabolic problems in humans, such as weight gain and a higher prevalence of diabetes.
Unlike hibernating rodents, who are almost comatose, grizzly bears move around occasionally during the dormant period, according to WSU researchers. Through observation studies of grizzly bears at the WSU Bear Center, researchers found that the movements follow a circadian rhythm with more activity during the day than at night.
To examine the circadian rhythm on a cellular level, researchers took cell samples from grizzly bears during both the active and hibernating seasons and conducted genetic analyses.
The study found that thousands of genes were expressed rhythmically in hibernating bear cells, indicating that the bears maintain a circadian rhythm by producing adenosine triphosphate (ATP), the body’s source of energy, later in the day during hibernation compared to the active season.
The researchers believe that altering the circadian rhythm during hibernation allows bears to benefit from the daily cycle without as much of the cost, helping them survive without food for months.
“It’s like setting a thermostat. If you want to conserve some energy, you turn down the thermostat, and this is essentially what the bears are doing,” Jansen said. “They’re using the ability to suppress the circadian rhythm, but they don’t stop the clock from running. It’s a really novel way of fine-tuning a metabolic process and energy expenditure in an animal.”