Gigantothermy

Gigantothermy describes an animal that is so big that it exchanges little heat with its surroundings. A large size leads to a low surface area to volume ratio, so the heat exchange rate is low compared to total size, and the rate at which a change in surface temperature causes a change in core body temperature is low as well. Body shape also affects surface area to volume ratio. Most animals that display gigantothermy have roughly spherical bodies. Insulation often contributes to a low heat exchange rate as well. Gigantotherms often benefit from circulation control, discussed in the following section. Overall, gigantothermic animals are said to have a large thermal inertia; they heat up or cool down slowly (Spotila, et al, 1991).

As the size of an animal increases and rate of heat exchange decreases, the terms endothermic and ectothermic become less significant, as large animals tend to have aspects of both endo- and ectothermy that are more accurately described as gigantothermic. Gigantothermic animals are found throughout the animal kingdom. Sea turtles, along with elephants and even some large dinosaurs, display gigantothermy (Spotila, et al, 1991).

Leatherback, photo courtesy of Scott Handy

The larger the turtle, the more significance gigantothermy has to its thermoregulation. Leatherbacks, as the largest sea turtles, benefit most from a low surface area to volume ratio, but all sea turtles benefit from a slow rate of heat exchange. A turtle’s carapace comprises a large percent of its surface area and is an excellent insulator. Leatherbacks have additional insulation beneath the carapace (Frair, et al, 1972) and are the only reptile with a layer of blubber similar to that of marine mammals (Hochschied, et al, 2002). Heat is more rapidly exchanged through sea turtles’ skin than through the carapace. The soft skin of the neck and flippers has the highest rate of heat exchange, followed by the plastron and finally the carapace. (Heath and McGinnis, 1980). The large surface area of the front flippers combined with this high rate causes them to exchange a good deal of heat with the surrounding water (Hochscheid, et al, 2002).

Thick insulation and a low surface area to volume ratio allow sea turtles to stay warmer than their surroundings. However, they must have physiological mechanisms that create the elevated body temperature maintained by gigantothermy.

Next: Regional Blood Flow

Home

 

This web site was completed by Katie Fitzpatrick in partial fulfillment of the requirements for Dr. Michael Dorcas's Biology 312, Animal Physiology, at Davidson College in Fall Semester 2005.

Visit other students' websites.

Please direct all comments and questions to Katie Fitzpatrick at kafitzpatrick@davidson.edu