Multiple Avenues to Adapt to Temperature.

• Position: BIRDS AND MAMMALS

Understanding the different ways organisms can adapt to environmental temperatures is central to understanding how they will respond to climate change. In a study appearing in Proceedings of the National Academy of Sciences, researchers use biophysical models of thermoregulation in order to reveal multiple ways birds and mammals adapt to a wide range of temperatures.

The Scholander-Irving model illustrates how warm-blooded birds and mammals maintain body temperature by balancing the rate of metabolic heat production with the rate of heat lost to the environment.

Body size has been shown to affect both rates and, as a result, influences an organism's thermal limits--larger species generally are able to deal with colder temperatures better than smaller species and vice versa. This has been used to explain Bergmann's rule, the geographic pattern of increasing size with decreasing temperature that is seen in some groups of animals.

However, after looking at the distribution of body sizes across temperatures on Earth, the scientists saw that birds and mammals of nearly every size basically live everywhere. Examples include tiny chickadees that can survive cold Alaskan winters, or elephants that live in some of the hottest parts of Africa. Clearly size is not everything, the scientists hypothesized. The researchers extended the Scholander-Irving model to understand how species adapt to temperature without changing size.

"We were interested in understanding ways other than body size that species can adapt their physiology and morphology in order to deal with environmental temperatures," says lead author Trevor Fristoe, a postdoctoral researcher in biology at Washington University, St. Louis, Mo. "So, we developed a method of measuring adaptation to the thermal environment independent of body size. We incorporated changes in both the rate of heat production via a species' metabolism as well as thermal conductance--the loss of bodily heat to the environment."

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