# Poikilotherm

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Organism with considerable internal temperature variation

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Thermoregulation in animals Ectotherm Endotherm Mesotherm Poikilotherm Homeothermy Heterothermy Stenotherm Eurytherm Thermolabile Thermostability Gigantothermy Kleptothermy Bradymetabolism Tachymetabolism Thermogenesis Thermobiology v t e

The [common frog](/source/Common_frog) is a poikilotherm and is able to function over a wide range of body core temperatures.

A **poikilotherm** ([/ˈpɔɪkələˌθɜːrm, pɔɪˈkɪləˌθɜːrm/](https://en.wikipedia.org/wiki/Help:IPA/English)) is an [animal](/source/Animal) (Greek *poikilos* – 'various', 'spotted', and *therme* – 'heat') whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress.[1] One of the most important stressors is outer environment temperature change, which can lead to alterations in [membrane lipid](/source/Membrane_lipid) order and can cause [protein unfolding and denaturation](/source/Denaturation_(biochemistry)) at elevated temperatures.[1] *Poikilotherm* is the opposite of *[homeotherm](/source/Homeotherm)* – an animal which maintains [thermal](/source/Thermal_regulation) [homeostasis](/source/Homeostasis). Usually the fluctuations are a consequence of variation in the [ambient environmental temperature](/source/Ambient_temperature). Many terrestrial [ectotherms](/source/Ectotherm) are poikilothermic.[2] However some ectotherms seek constant-temperature environments to the point that they are able to maintain a constant internal temperature, and are considered actual or practical [homeotherms](/source/Homeotherm).[3] 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](/source/Ectotherm) more generally.

Poikilothermic animals include types of vertebrate animals, specifically some fish, amphibians, and reptiles, as well as many [invertebrate](/source/Invertebrate) animals. The [naked mole-rat](/source/Naked_mole-rat)[4][5] and [sloths](/source/Sloth)[6] are some of the rare mammals which are poikilothermic.

## Etymology

The term derives from [Greek](/source/Ancient_Greek) *poikilos* (ποικίλος), meaning "varied," ultimately from a root meaning "dappled" or "painted," and *thermos* (θερμός), meaning "heat".[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Physiology

Sustained energy output of a poikilotherm (a [lizard](/source/Lizard)) and a [homeotherm](/source/Homeotherm) (a [mouse](/source/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.

Poikilotherm animals must be able to function over a wider range of temperatures than homeotherms. The speed of most chemical reactions vary with temperature, and in order to function poikilotherms may have four to ten [enzyme](/source/Enzyme) systems that operate at different temperatures for an important chemical reaction.[7] As a result, poikilotherms often have larger, more complex [genomes](/source/Genome) than homeotherms in the same [ecological niche](/source/Ecological_niche). [Frogs](/source/Frog) are a notable example of this effect, though their complex development is also an important factor in their large genome.[8]

Because their metabolism is variable and generally below that of homeothermic [animals](/source/Animals), sustained high-energy activities like powered [flight](/source/Flight) in large animals or maintaining a large [brain](/source/Brain) is generally beyond poikilotherm animals.[9] 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](/source/Metabolism) to heat or cool themselves, total energy requirement over time is low. For the same body weight, poikilotherms need only 5 to 10% of the energy of [homeotherms](/source/Homeotherm).[10]

## Adaptations in poikilotherms

- Some adaptations are behavioral. Lizards and [snakes](/source/Snake) bask in the sun in the early morning and late evening, and seek shelter around noon.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- The eggs of the [yellow-faced bumblebee](/source/Yellow-faced_bumblebee) are unable to regulate heat. A behavioral adaptation to combat this is incubation, where to maintain the internal temperatures of eggs, the queen and her workers will incubate the brood almost constantly, by warming their abdomens and touching them to the eggs. The bumblebee generates heat by shivering flight muscles even though it is not flying. [*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Termite](/source/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.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Tuna](/source/Tuna) are able to warm their entire bodies through a heat exchange mechanism called the [rete mirabile](/source/Rete_mirabile), which helps keep heat inside the body, and minimises the loss of heat through the [gills](/source/Gill). They also have their swimming muscles near the center of their bodies instead of near the surface, which minimises heat loss.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Gigantothermy](/source/Gigantothermy) means growing to large size in order to reduce heat loss, as in [sea turtles](/source/Sea_turtle) and [ice-age](/source/Last_glacial_period) [megafauna](/source/Megafauna#Evolution_of_large_body_size). As body size increases, body volume increases proportionally faster than does body surface. Less body surface area per unit body volume tends to reduce heat loss.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

- [Camels](/source/Camel), although they are homeotherms, thermoregulate using a method termed "temperature cycling" to conserve energy. In hot deserts, they allow their body temperature to rise during the day and fall during the night, adjusting their body temperature to cycle over approximately 6 °C.[11]

## Ecology

It is comparatively easy for a poikilotherm to accumulate enough energy to reproduce. Poikilotherms at the same [trophic level](/source/Trophic_level) often have much shorter generations than homeotherms: weeks rather than years.[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] Such applies even to animals with similar ecological roles such as [cats](/source/Cat) and [snakes](/source/Snake).

This difference in energy requirement also means that a given food source can support a greater density of poikilothermic animals than homeothermic animals.[12] 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 and in more effective, specialized ways (e.g. chimpanzees actively seeking out and collecting army ants with sticks versus the typical poikilotherm sit-and-wait strategy).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## In medicine

In medicine, loss of normal thermoregulation is referred to as *poikilothermia*. This can be seen in [compartment syndrome](/source/Compartment_syndrome) and with use of [sedative-hypnotics](/source/Sedative-hypnotic) like [barbiturates](/source/Barbiturate), [ethanol](/source/Ethanol), and [chloral hydrate](/source/Chloral_hydrate).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*] [REM sleep](/source/REM_sleep) is considered a poikilothermic state in humans.[13] Poikilothermia is one of the signs of [acute limb ischemia](/source/Acute_limb_ischemia).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Notes

1. ^ [***a***](#cite_ref-:0_1-0) [***b***](#cite_ref-:0_1-1) Guschina, Irina A.; Harwood, John L. (2006). "Mechanisms of temperature adaptation in poikilotherms". *FEBS Letters*. **580** (23): 5477–5483. [Bibcode](/source/Bibcode_(identifier)):[2006FEBSL.580.5477G](https://ui.adsabs.harvard.edu/abs/2006FEBSL.580.5477G). [doi](/source/Doi_(identifier)):[10.1016/j.febslet.2006.06.066](https://doi.org/10.1016%2Fj.febslet.2006.06.066). [ISSN](/source/ISSN_(identifier)) [1873-3468](https://search.worldcat.org/issn/1873-3468). [PMID](/source/PMID_(identifier)) [16824520](https://pubmed.ncbi.nlm.nih.gov/16824520). [S2CID](/source/S2CID_(identifier)) [25197515](https://api.semanticscholar.org/CorpusID:25197515).

1. **[^](#cite_ref-hilde_2-0)** Hildebrand, Milton; Goslow, G.E., Jr. (2001). *Analysis of Vertebrate Structure*. Hildebrand, Viola (principle illust.). New York, NY: Wiley. p. 429. [ISBN](/source/ISBN_(identifier)) [0-471-29505-1](https://en.wikipedia.org/wiki/Special:BookSources/0-471-29505-1).{{[cite book](https://en.wikipedia.org/wiki/Template:Cite_book)}}: CS1 maint: multiple names: authors list ([link](https://en.wikipedia.org/wiki/Category:CS1_maint:_multiple_names:_authors_list))

1. **[^](#cite_ref-3)** Riemer, Kristina; Anderson-Teixeira, Kristina J.; Smith, Felisa A.; Harris, David J.; Ernest, S.K. Morgan (2018). "Body size shifts influence effects of increasing temperatures on ectotherm metabolism". *Global Ecology and Biogeography*. **27** (8): 958. [Bibcode](/source/Bibcode_(identifier)):[2018GloEB..27..958R](https://ui.adsabs.harvard.edu/abs/2018GloEB..27..958R). [doi](/source/Doi_(identifier)):[10.1111/geb.12757](https://doi.org/10.1111%2Fgeb.12757).

1. **[^](#cite_ref-Daly_et_al.,_(1997)_4-0)** Daly, T.J.M.; Williams, L.A.; Buffenstein, R. (1997). ["Catecholaminergic innervation of interscapular brown adipose tissue in the naked mole-rat (*Heterocephalus glaber*)"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1467613). *Journal of Anatomy*. **190**: 321–326. [doi](/source/Doi_(identifier)):[10.1046/j.1469-7580.1997.19030321.x](https://doi.org/10.1046%2Fj.1469-7580.1997.19030321.x). [PMC](/source/PMC_(identifier)) [1467613](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1467613).

1. **[^](#cite_ref-Sherwin,_(2010)_5-0)** Sherwin, C.M. (2010). "The husbandry and welfare of non-traditional laboratory rodents". In Hubrecht, R.; Kirkwood, J. (eds.). *UFAW Handbook on the Care and Management of Laboratory Animals*. Wiley-Blackwell. Chapter 25, pp. 359–369.

1. **[^](#cite_ref-6)** Britton, S.W.; Atkinson, W.E. (1938). "Poikilothermism in the Sloth". *Journal of Mammalogy*. **19** (1): 94. [doi](/source/Doi_(identifier)):[10.2307/1374287](https://doi.org/10.2307%2F1374287). [JSTOR](/source/JSTOR_(identifier)) [1374287](https://www.jstor.org/stable/1374287).

1. **[^](#cite_ref-7)** Cavalier-Smith, T. (1991). "Coevolution of vertebrate genome, cell, and nuclear sizes". *Symposium on the Evolution of Terrestrial Vertebrates*: 51–86.

1. **[^](#cite_ref-8)** Ryan Gregory, T. (1 January 2002). "Genome size and developmental complexity". *Genetica*. **115** (1): 131–146. [doi](/source/Doi_(identifier)):[10.1023/A:1016032400147](https://doi.org/10.1023%2FA%3A1016032400147). [PMID](/source/PMID_(identifier)) [12188045](https://pubmed.ncbi.nlm.nih.gov/12188045). [S2CID](/source/S2CID_(identifier)) [24565842](https://api.semanticscholar.org/CorpusID:24565842).

1. **[^](#cite_ref-9)** Willmer, P., Stone, G., & Johnston, I. A. (2000): Environmental physiology of animals. *Blackwell Science*, London. 644 pages, [ISBN](/source/ISBN_(identifier)) [0-632-03517-X](https://en.wikipedia.org/wiki/Special:BookSources/0-632-03517-X).

1. **[^](#cite_ref-10)** Campbell, N. A., Reece, J. B., et al. (2002). Biology. 6th edition. Benjamin / Cummings Publishing Company.

1. **[^](#cite_ref-11)** Hill, Richard (2016). *Animal Physiology*. Sunderland, MA: Sinauer Associates. p. 270. [ISBN](/source/ISBN_(identifier)) [978-1605354712](https://en.wikipedia.org/wiki/Special:BookSources/978-1605354712).

1. **[^](#cite_ref-12)** 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](https://www.jstor.org/stable/3544877)

1. **[^](#cite_ref-13)** [Leon Rosenthal](https://en.wikipedia.org/w/index.php?title=Physiologic_Processes_During_Sleep&action=edit&redlink=1) (2009). "3". In Teofilo Lee-Chiong (ed.). *Sleep Medicine Essentials*. Wiley-Blackwell. p. 12.

## External links

- The dictionary definition of [*poikilotherm*](https://en.wiktionary.org/wiki/Special:Search/poikilotherm) at Wiktionary

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Adapted from the Wikipedia article [Poikilotherm](https://en.wikipedia.org/wiki/Poikilotherm) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Poikilotherm?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.