World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0002008686
Reproduction Date:

Title: Poikilotherm  
Author: World Heritage Encyclopedia
Language: English
Subject: Heterothermy, Physiology of dinosaurs, Reptile, Bradymetabolism, Eurytherm
Publisher: World Heritage Encyclopedia


The Common frog is a poikilotherm and is able to function over a wide range of body core temperatures.

A poikilotherm is an thermal homeostasis. Usually the variation is a consequence of variation in the ambient environmental temperature. Many terrestrial ectotherms are poikilothermic.[1] However some ectotherms remain in temperature-constant environments to the point that they are actually able to maintain a constant internal temperature (i.e. are homeothermic). It is this distinction that often makes the term "poikilotherm" more useful than the vernacular "cold-blooded", which is sometimes used to refer to ectotherms more generally. Poikilothermic animals include types of vertebrate animals, specifically fish, amphibians, and reptiles, as well as a large number of invertebrate animals. The naked mole-rat is the only mammal that is currently thought to be poikilothermic.[2][3]


The term derives from ancient Greek: poikilos (ποικίλος), meaning "varied"; and thermos (θερμός), meaning "heat".[4]


Sustained energy output of a poikilotherm (a lizard) and a homeotherm (a mouse) as a function of core body temperature. The homeotherm has a much higher output, but can only function over a very narrow range of body temperatures.

For an important chemical reaction, poikilotherms may have four to ten enzyme systems that operate at different temperatures.[5] 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, though their complex development is likely more important.[6]

Because their metabolism is variable and generally below that of homeothermic animals, sustained high-energy activities like powered flight in large animals or maintaining a large brain is generally beyond poikilotherm animals.[7] The metabolism of poikilotherms favors strategies such as sit-and-wait hunting over chasing prey for larger animals with high movement cost. As they do not use their metabolisms to heat or cool themselves, total energy requirement over time is low. For the same body weight, poikilotherms need only 50 to 10% of the energy of homeotherms.[8]

Adaptations in poikilotherms

  • Some adaptations are behavioral. Lizards and snakes bask in the sun in the early morning and late evening, and seek shelter around noon.
  • Termite mounds are usually oriented in a north-south direction so that they absorb as much heat as possible around dawn and dusk and minimise heat absorption around noon.
  • Tuna are able to warm their entire bodies through a heat exchange mechanism called the rete mirabile, which helps keep heat inside the body, and minimises the loss of heat through the gills. They also have their swimming muscles near the center of their bodies instead of near the surface, which minimises heat loss.
  • Gigantothermy means using a low ratio of surface area to volume to minimise heat loss, such as in sea turtles.


It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms at the same trophic level often have much shorter generations than homeotherms: weeks rather than years. Such applies even to animals with similar ecological roles such as cats and snakes.

This difference in energy requirement also means that a given food source can support a greater density of poikilothermic animals than homeothermic animals.[9] This is reflected in the predator-prey ratio which is usually higher in poikilothermic fauna compared to homeothermic ones. However, when homeotherms and poikilotherms have similar niches, and compete, the homeotherm can often drive poikilothermic competitors to extinction, because homeotherms can gather food for a greater fraction of each day.

In medicine

In medicine, loss of normal thermoregulation in humans is referred to as "poikilothermia". This is usually seen with sedative and hypnotic drugs or in 'compartment syndrome'. For example, barbiturates, ethanol, and chloral hydrate may precipitate this effect. REM sleep is also considered a poikilothermic state in humans.[10]


  1. ^ Milton Hildebrand; G. E. Goslow, Jr. Principal ill. Viola Hildebrand. (2001). Analysis of vertebrate structure. New York: Wiley. p. 429.  
  2. ^ Daly, T.J.M., Williams, L.A. and Buffenstein, R., (1997). Catecholaminergic innervation of interscapular brown adipose tissue in the naked mole-rat (Heterocephalus glaber). Journal of Anatomy, 190: 321-326. doi:10.1046/j.1469-7580.1997.19030321.x
  3. ^ Sherwin, C.M. (2010). The Husbandry and Welfare of Non-traditional Laboratory Rodents. In "UFAW Handbook on the Care and Management of Laboratory Animals", R. Hubrecht and J. Kirkwood (Eds). Wiley-Blackwell. Chapter 25, pp. 359-369
  4. ^ (Greek) Triantafyllidis Online Lexicon, ποικιλόθερμος. Retrieved on 2007-01-12.
  5. ^ Cavalier-Smith, T. "Coevolution of vertebrate genome, cell, and nuclear sizes". Symposium on the Evolution of Terrestrial Vertebrates: 51–86. 
  6. ^ Ryan Gregory, T. (1 January 2002). "Genome size and developmental complexity". Genetica 115 (1): 131–146.  
  7. ^ Willmer, P., Stone, G., & Johnston, I. A. (2000): Environmental physiology of animals. Blackwell Science, London. 644 pages, ISBN 0-632-03517-X.
  8. ^ Campbell, N. A., Reece, J. B., et al. (2002). Biology. 6th edition. Benjamin / Cummings Publishing Company.
  9. ^ Steen, J.B, Steen, H. & Stenseth, N.C. (1991): Population Dynamics of Poikilotherm and Homeotherm Vertebrates: Effects of Food Shortage. OICOS Vol. 60, No 2 (March, 1991), pp 269-272. summary
  10. ^  
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.