This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (February 2009)

Look up poikilotherm in Wiktionary, the free dictionary.

A poikilotherm is an animal whose internal temperature varies along with that of the ambient environmental temperature. Most, but not all, ectotherms are poikilothermic. The opposite of poikilothermy is homeothermy, referring to animals that maintain a constant body temperature.^[1] The term is used as a more exact description of the vernacular "cold-blooded".

Contents 1 Etymology 2 Physiology 3 Ecological niches 4 In medicine 5 See also 6 Notes

[edit] Etymology

The term derives from Ancient Greek, poikilos (ποικίλος), meaning "varied"; and thermos (θερμός), meaning "warm".^[2]

[edit] Physiology

For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures. As a result, poikilotherms often have larger, more complex genomes than homeotherms in the same ecological niche. Frogs are a notable example of this effect.

Because their metabolism is so variable, poikilothermic animals do not easily support complex, high-energy organ systems such as brains or wings.^{[citation needed]} Poikilothermic animals do not use their metabolisms to heat or cool themselves. For the same body weight, poikilotherms need half to 1/10 of the energy of homeotherms, and thus eat half to 1/10 of the biomass.

[edit] Ecological niches

It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms in the same ecological niche often have much shorter lifetimes than homeotherms: weeks rather than years.^{[citation needed]}

This energy difference also means that a given niche of a given ecology can support three to ten times the number of poikilothermic animals as homeothermic animals. However, in a given niche, homeotherms often drive poikilothermic competitors to extinction because homeotherms can gather food for a greater fraction of each day.

Poikilotherms succeed in some niches, such as islands, or distinct bioregions (such as the small bioregions of the Amazon basin). These often do not have enough food to support a viable breeding population of homeothermic animals. In these niches, poikilotherms such as large lizards, crabs and frogs supplant homeotherms such as birds and mammals.

[edit] In medicine

In medicine, loss of normal thermoregulation in humans is referred to as "poikilothermia". This is usually seen with sedative and hypnotic drugs. For example, barbiturates, ethanol, and chloral hydrate may precipitate this effect.

[edit] See also

• Ecothermy
• Ectotherm
  • Gigantothermy
• Endotherm
• Homeotherm

[edit] Notes

v • d • e Thermoregulation in animals Ectothermy · Endothermy Poikilothermy · Heterothermy · Homeothermy (Gigantothermy) Bradymetabolism · Tachymetabolism