Colorado State University Research Shows Global Warming May Have Detrimental Effects on Hibernating Animals

A changing, warmer global climate over certain parts of the country may have a harsh impact on animals, said Greg Florant, a professor of biology at Colorado State University. A warm winter could mean animals that hibernate, such as marmots, groundhogs and ground squirrels, will wake up sooner and possibly before there is an adequate supply of food available in their environment.

"Warmer temperatures can definitely shift and change these hibernation cycles," Florant said. In the Midwest, for example, recent warm winter temperatures are expected to raise the metabolic rate of the 13-lined squirrel, an animal that hibernates in the ground.

Florant has spent a large part of his career studying how marmots and ground squirrels use fats and other nutrients to hibernate and regulate energy metabolism. Recently, he has been researching the effects of different ambient temperatures on golden-mantled ground squirrels as they prepare for and undergo hibernation. Florant, his collaborator Susan Fried at the University of Maryland Medical School and Colorado State undergraduate student Melanie Richter have found a correlation between temperature and the protein hormone leptin, which plays a crucial role in regulating an animal’s body weight, metabolism and reproductive functions.

The concentration of leptin decreases in ground squirrels when they are kept at a warm ambient temperature, regardless of whether they are in hibernation, Florant said. This is because the warm ambient temperature speeds up their metabolism, causing a rapid drop in fat reserves which, in turn, decreases plasma leptin. Decreased levels of leptin stimulates food intake and is usually associated with the coming of spring. Researchers have found that ground squirrels exposed to normal cold winter temperatures have abundant fat deposits, usually have higher plasma leptin concentrations and do not feed.

Rocky Mountain hibernators, such as the yellow-bellied marmot and golden-mantled ground squirrel, living where temperatures have remained cold throughout this winter and where snowpack has been substantial, will likely not be affected this year. In the past, dry winters with a lack of snowpack resulted in the ground freezing further down, and this caused increased mortality in some hibernating squirrels.

Hibernating animals such as groundhogs are often seen traditionally as predictors of weather, Florant said. However, these animals can teach researchers more about the complex behavior of hypometabolism – a regulated decrease in metabolic rate – where the animal can turn off their appetites and slow their breathing to a point which would be lethal to other animals. Florant investigates how changes in metabolism during hibernation relate to the regulation of food intake and obesity.

Tissue samples taken from marmots in Florant’s lab allow researchers to identify biochemical processes and genes that are active during hibernation as opposed to genes that are active when the animals are feeding or engaging in other behaviors.