Heterothermy

Heterothermy (from Greek: heteros = "other" thermē = "heat.") is a physiological term for animals that exhibit characteristics of both poikilothermy and homeothermy.

Temporal heterothermy

Temporal heterothermy refers to animals that are poikilothermic or homeothermic for a portion of the day, or year. More often than not, it is used as a way to dissociate the fluctuating metabolic rates seen in some small mammals and birds (e.g. bats and hummingbirds), from those of traditional cold blooded animals. In many bat species, body temperature and metabolic rate are elevated only during activity. When at rest, these animals reduce their metabolisms drastically, which results in their body temperature dropping to that of the surrounding environment. This makes them homeothermic when active, and poikilothermic when at rest.

Regional heterothermy

Regional heterothermy describes organisms that are able to maintain different temperature "zones" in different regions of the body. This usually occurs in the limbs, and is made possible through the use of counter-current heat exchangers, such as the rete mirabile found in tuna and certain birds.^[1] These exchangers equalise the temperature between hot arterial blood going out to the extremities and cold venous blood coming back, thus reducing heat loss. Penguins and many arctic birds use these exchangers to keep their feet at roughly the same temperature as the surrounding ice. This keeps the birds from getting stuck on an ice sheet. Other animals, like the Leatherback Sea Turtle, use the heat exchangers to gather, and retain heat generated by their muscular flippers.^[2] There are even some insects which possess this mechanism, the best-known example being bumblebees, which exhibit counter-current heat exchange at the point of constriction between the mesosoma ("thorax") and metasoma ("abdomen"); heat is retained in the thorax and lost from the abdomen.^[3] Using a very similar mechanism, the internal temperature of a honeybee's thorax can exceed 45°C while in flight.

References

1. ^ Katz, S, L. 2002. ‘Design of heterothermic muscle in fish’, The Journal of Experimental Biology 205, 2251–2266.
2. ^ James, Michael; Mrosovsky, N. 2004. 'Body temperatures of leatherback turtles (Dermochelys coriacea) in temperate waters off Nova Scotia, Canada', Canadian Journal of Zoology 82, 1302–1306
3. ^ Heinrich, B. 1976. 'Heat exchange in relation to blood flow between thorax and abdomen in bumblebees', Journal of Experimental Biology 64, 561–585

External links

• Thermobiology of bats