Poikilotherm

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poikilotherm

[pȯi′kil·ə‚thərm]
(zoology)
An animal, such as reptiles, fishes, and invertebrates, whose body temperature varies with and is usually higher than the temperature of the environment; a cold-blooded animal.

Poikilotherm

 

a cold-blooded animal, that is, an animal with a variable body temperature that changes as a function of the temperature of the environment. Poikilotherms include all invertebrates; the only poikilothermic vertebrates are fishes, amphibians, and reptiles.

The body temperature of poikilotherms is generally only 1° or 2° higher than, or equal to, that of the environment. Thermoregulation is imperfect. In many poikilotherms the body temperature rises as a result of muscular work or the absorption of solar heat. For example, the body temperature of bumblebees in flight may reach 38° or even 44°C at an air temperature of 4° to 8°C. However, after the cessation of flight the body cools rapidly to the temperature of the environment. If the external temperature rises above or falls below optimal limits, poikilotherms become torpid or perish. Many of them are in torpor a large part of the year; for example, the turtle Testudo horsfieldi is active only three months of the year. The absence of perfect thermoregulatory mechanisms in poikilotherms may be explained by the relatively poor development of their nervous systems (especially the central nervous system), a level of metabolism approximately 20 to 30 times lower than that of homeo-therms, and other features associated with the fact that poikilotherms have a more primitive organization than birds and mammals.

References in periodicals archive ?
Lags have also been found in the bones of reptiles and amphibians and have until now been assumed to be limited to ectotherms - cold-blooded animals - that are more subject to the whims of harsh environments.
What applies to cold-blooded animals such as poison frogs doesn't necessarily apply to warm-blooded animals such as humans," Santos said.
The senseless killing of Monica Lynne Leech in Thousand Oaks reminds us that there is no safety from cold-blooded animals who prey on the defenseless.
They explained that since crocodiles are cold-blooded animals, the temperature of the environment affects their body temperature and metabolic rate.
Metabolic and lung ventilation rates in cold-blooded animals are about five percent of a similarly sized warm-blooded animal.
The ability to better control the freezing temperature of supercooled water could be critical for a variety of applications, including the survival of cold-blooded animals, the cryo-preservation of cells and tissues, the protection of crops from freezing, and the ability to understand and trigger cloud formation.
This needs to be taken into account for scientific studies of other cold-blooded animals, or ectotherms, such as reptiles and amphibians," he said.
The discovery is likely to fuel the debate about whether dinosaurs were warm- or cold-blooded animals, but "mostly what it does is show us that the best discoveries are made when we least expect them," says Horner.
Based on the energy they consumed when moving, many dinosaurs were probably endothermic, athletic animals because their energy requirements during walking and running were too high for cold-blooded animals to produce.
The bones of some Cretaceous birds have growth rings, a feature common among cold-blooded animals.