What does poikilotherm mean?
A poikilotherm is an animal or other organism whose body temperature changes with the temperature of its surroundings rather than remaining relatively constant. Such animals may warm themselves by basking in sunlight, moving into warmer areas, or absorbing heat directly from water or soil, and they often become less active when conditions become cold. Most fishes, reptiles, amphibians, and many invertebrates are poikilotherms. The term is more precise than the familiar expression “cold-blooded,” because it describes a physiological pattern rather than merely suggesting that an animal is unimaginative or unfeeling. Poikilothermy contrasts with homeothermy, in which a relatively stable internal temperature is maintained, and with endothermy, in which metabolic heat is the principal source of body heat. The word is especially useful in discussions of animal physiology, climate adaptation, ecology, and differences between ectothermic and endothermic organisms.
nounA poikilotherm is an organism whose internal body temperature largely follows, and changes with, the temperature of its surroundings. Many fishes, reptiles, amphibians, and invertebrates are poikilotherms.
- An organism whose body temperature varies substantially with the temperature of its surroundings.
"The lizard basked on the warm stone because, as a poikilotherm, it relied on external heat to raise its body temperature."
"Most fish in the lake are poikilotherms, so their activity levels fall as the water becomes colder."
"The comparison between the poikilotherm and the endotherm demonstrates how differently animals regulate body temperature."
The plural is used when referring to multiple organisms of this physiological type.
"Many poikilotherms reduce their activity during periods of extreme cold."
A snake may warm itself in the sun, but a tiny lizard in the shade can cool down with equal ease: both are masters of taking the environment’s temperature.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does poikilotherm come from?
The word was formed in the late 19th century from Greek poikilos, meaning “varying” or “wandering,” and thermē, meaning “heat.” The combining form thermo- derives from the same Greek root and appears in English words such as thermometer, thermal, and thermotherapy. In zoological terminology, the word developed alongside homeotherm and contrasts organisms with variable body temperatures with those that maintain a relatively stable temperature.
Related word forms
How poikilotherm is actually used
This is a technical biological term used chiefly in zoology, ecology, and comparative physiology. In general writing, “cold-blooded animal” is more accessible, although it can sound disparaging and does not convey the precise physiological criterion as clearly.
Easily confused with poikilotherm
An ectotherm primarily relies on environmental heat, whereas a poikilotherm is defined more precisely by having a body temperature that varies with the environment.
A homeotherm maintains a relatively stable internal body temperature, unlike a poikilotherm, whose temperature changes with its surroundings.