Coping with stress is not just a human concern. Animals also deal with a changing and uncertain environment, and stress hormones, like cortisol, control their responses. Trent University graduate student, Lanna Desantis and colleagues discovered high levels of cortisol in the everyday lives of northern and southern flying squirrels.
According to the study, flying squirrels have cortisol levels that are 10 to 20 times higher than in humans, and up to 200 times higher than levels found in birds, giving them some of the highest stress hormone levels among the vertebrates (fish, amphibians, reptiles, birds and mammals).
Surprisingly, the squirrels also show that an extremely low proportion of all of this cortisol is bound to an important “carrier protein” – a protein found in blood that helps prevent potent stress hormones from constantly activating the body’s tissues, until needed in response to stressful situations. Without binding to this carrier protein, flying squirrels have 90 per cent, or more, of their cortisol left to circulate freely in the blood. This implies they lack protection from stress hormones themselves and suggests a new way that stress physiology operates, which is different from textbook examples on humans, mice and rats.
“The intriguing thing is, cortisol levels this high would most likely mean death in other species. The fact that northern and southern flying squirrels show no physical detriment is truly an anomaly,” said Ms. Desantis, the lead author on the paper. She also notes, “It’s often these exceptions to the rule that lead to the most interesting science, and that allow us the greatest insight into the ways of the natural world. The physiology of these squirrels is similar only to one other group of animals - a small number of monkeys in South America, a group well known to stress physiologists. Now we’ve found a second group that doesn’t seem to follow the rules of stress regulation.”
The authors compared their data to 89 other vertebrate species. The study revealed that the majority of all other species have carrier protein sufficient to bind most of their circulating stress hormone, leaving only about 10 per cent free in the blood. This means that body tissues of most vertebrates are almost always protected from the potentially harmful effects of cortisol. Flying squirrels thus appear to be unique.
The action of stress hormones in wildlife is similar to that in people. Chronically high cortisol, which occurs during prolonged periods of stress, can cause fatigue, sickness, indigestion, reproductive problems, and even ulcers. These things happen in wildlife too, when animals are exposed to chronic, long-term stressors such as habitat loss and human disturbance.
Flying squirrels however, do not appear to show any of the negative consequences of exposure to stress hormones despite their high and persistent levels of cortisol, which were measured over the course of an entire year.
“Stress hormones and carrier proteins are key to survival, and to an animal’s ability to adapt to, and compensate for, large changes in their environment,” Ms. Desantis explains. “Knowledge of these unique adaptations also provides a window to the past – such as the shifts that the monkeys and flying squirrels may have experienced when inhabiting North, Central and South America thousands or millions of years ago.”
The discovery was published in the current issue of the esteemed journal, Functional Ecology. The tests were conducted at the University of Toronto, in conjunction with Drs. Rudy Boonstra, and collaborators, Brendan Delehanty and Jason Weir. Lanna Desantis is a Ph.D. student in the Environmental and Life Sciences Program at Trent University. She came to Trent in 2011 to work with Drs. Gary Burness (Professor of Biology) and Jeff Bowman (Research Scientist, Ontario Ministry of Natural Resources) to continue her studies on the physiology and genetics of how and why these gliding mammals came to have such a rare stress physiology.
Posted on Friday, March 1, 2013.