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a state of sharply decreased life activity that occurs in cold-blooded (poikilothermic) animals as an adaptation for surviving unfavorable environmental conditions, especially insufficient warmth, moisture, and food. In torpor, the animal is immobile and stops eating. Gas exchange and other physiological processes are severely inhibited (see ANABIOSIS).
Winter torpor sets in when the temperature of the environment drops. It is characteristic of animals in the northern and temperate latitudes, including many terrestrial and aquatic invertebrates, fishes, amphibians (frogs, tritons, and toads), and reptiles (lizards, snakes). During winter, some of these animals hide under the bark of trees, under fallen leaves, in tree hollows, in rodent burrows, or under rocks or dig into the ground or moss. Others bury themselves in mud. Animals become torpid at different environmental temperatures. For example, some insects, fishes, and amphibians become torpid, or dormant, at temperatures lower then 10°-15°C, and others, only at 0°C.
The duration of torpor depends, to a considerable extent, on climatic conditions and on the quantity of food products stored in the body in advance. The body temperature of an animal in torpor is almost the same as the environmental temperature and only rarely drops below 0°C. However, the majority of animals subject to torpor are capable of “supercooling”—that is, they will not freeze to death if the temperature drops below 0°C.
Summer torpor, which is far less common than winter torpor, is associated with drought. When a body of water dries up, some fishes (Dipnoi, for example), amphibians, and reptiles become torpid. If the vegetation in their habitat is burned or dried out, some terrestrial snails and reptiles (for example, steppe tortoises) become torpid. In summer torpor, animals either become dehydrated (lose a great deal of water) or hide in moist shelters, such as mud.
Under the effect of low temperatures, some birds may experience a temporary decrease in body temperature and the onset of a state similar to torpor in poikilothermic animals. The study of torpor has great practical significance for devising methods of controlling agricultural pests and the carriers of human diseases.
Hibernation in mammals is analogous to torpor in coldblooded animals. Some scientists use the term “hibernation” to designate the phenomenon of dormancy in both mammals and cold-blooded animals.