{{short description|Organism with considerable internal temperature variation}} {{Expert needed|biology|reason=Article could have a lot more information|date=July 2016}} {{Thermoreg}} [[File:Bgbo frosch ies.jpg|thumb|250 px|right|The [[common frog]] is a poikilotherm and is able to function over a wide range of body core temperatures.]] A '''poikilotherm''' ({{IPAc-en|ˈ|p|ɔɪ|k|ə|l|ə|ˌ|θ|ɜr|m|,_|p|ɔɪ|ˈ|k|ɪ|l|ə|ˌ|θ|ɜr|m}}) is an [[animal]] (Greek ''poikilos'' – 'various', 'spotted', and ''therme'' – 'heat') whose internal temperature varies considerably. Poikilotherms have to survive and adapt to environmental stress.<ref name=":0">{{Cite journal|last1=Guschina|first1=Irina A.|last2=Harwood|first2=John L.|date=2006|title=Mechanisms of temperature adaptation in poikilotherms|journal=FEBS Letters|language=en|volume=580|issue=23|pages=5477–5483|doi=10.1016/j.febslet.2006.06.066|pmid=16824520|s2cid=25197515 |issn=1873-3468|doi-access=|bibcode=2006FEBSL.580.5477G }}</ref> One of the most important stressors is outer environment temperature change, which can lead to alterations in [[membrane lipid]] order and can cause [[Denaturation (biochemistry)|protein unfolding and denaturation]] at elevated temperatures.<ref name=":0"/> ''Poikilotherm'' is the opposite of ''[[homeotherm]]'' – an animal which maintains [[thermal regulation|thermal]] [[homeostasis]]. Usually the fluctuations are a consequence of variation in the [[Ambient temperature|ambient environmental temperature]]. Many terrestrial [[ectotherm]]s are poikilothermic.<ref name=hilde>{{cite book |first1=Milton |last1=Hildebrand |first2=G.E., Jr. |last2=Goslow |year=2001 |title=Analysis of Vertebrate Structure |others=Hildebrand, Viola (principle illust.) |publisher=Wiley |place=New York, NY |isbn=0-471-29505-1 |page=429 }}</ref> 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 [[homeotherm]]s.<ref>{{cite journal |last1=Riemer |first1=Kristina |last2=Anderson-Teixeira |first2=Kristina J. |last3=Smith |first3=Felisa A. |last4=Harris |first4=David J. |last5=Ernest |first5=S.K. Morgan |year=2018 |title=Body size shifts influence effects of increasing temperatures on ectotherm metabolism |journal=Global Ecology and Biogeography |volume=27 |issue=8 |page=958 |bibcode=2018GloEB..27..958R |doi=10.1111/geb.12757 }}</ref> It is this distinction that often makes the term ''poikilotherm'' more useful than the vernacular "cold-blooded", which is sometimes used to refer to [[ectotherm]]s more generally.
Poikilothermic animals include types of vertebrate animals, specifically some fish, amphibians, and reptiles, as well as many [[invertebrate]] animals. The [[naked mole-rat]]<ref name="Daly et al., (1997)">{{cite journal |last1=Daly |first1=T.J.M. |last2=Williams |first2=L.A. |last3=Buffenstein |first3=R. |year=1997 |title=Catecholaminergic innervation of interscapular brown adipose tissue in the naked mole-rat (''Heterocephalus glaber'') |journal=Journal of Anatomy |volume=190 |pages=321–326 |doi=10.1046/j.1469-7580.1997.19030321.x |pmc=1467613 }}</ref><ref name="Sherwin, (2010)">{{cite book |last=Sherwin |first=C.M. |year=2010 |section=The husbandry and welfare of non-traditional laboratory rodents |title=UFAW Handbook on the Care and Management of Laboratory Animals |editor1-first=R. |editor1-last=Hubrecht |editor2-first=J. |editor2-last=Kirkwood |publisher=Wiley-Blackwell |at=Chapter 25, pp. 359–369 }}</ref> and [[sloth]]s<ref>{{cite journal |last1=Britton |first1=S.W. |last2=Atkinson |first2=W.E. |year=1938 |title=Poikilothermism in the Sloth |journal=Journal of Mammalogy |volume=19 |issue=1 |page=94 |doi=10.2307/1374287 |jstor=1374287}}</ref> are some of the rare mammals which are poikilothermic.
== Etymology == The term derives from [[Ancient Greek|Greek]] ''poikilos'' ({{lang|el|{{math|ποικίλος}}}}), meaning "varied," ultimately from a root meaning "dappled" or "painted," and ''thermos'' ({{lang|el|{{math|θερμός}}}}), meaning "heat".{{cn|date=March 2025}}
== Physiology == [[File:Homeothermy-poikilothermy.png|thumb|250 px|right|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.]]
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]] systems that operate at different temperatures for an important chemical reaction.<ref>{{cite journal|last=Cavalier-Smith|first=T.|date=1991|title=Coevolution of vertebrate genome, cell, and nuclear sizes|journal=Symposium on the Evolution of Terrestrial Vertebrates|pages=51–86}}</ref> As a result, poikilotherms often have larger, more complex [[genome]]s than homeotherms in the same [[ecological niche]]. [[Frog]]s are a notable example of this effect, though their complex development is also an important factor in their large genome.<ref>{{cite journal|last=Ryan Gregory|first=T.|title=Genome size and developmental complexity|journal=Genetica|date=1 January 2002|volume=115|issue=1|pages=131–146|doi=10.1023/A:1016032400147|pmid=12188045|s2cid=24565842}}</ref>
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.<ref>Willmer, P., Stone, G., & Johnston, I. A. (2000): Environmental physiology of animals. ''Blackwell Science'', London. 644 pages, {{ISBN|0-632-03517-X}}.</ref> 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 [[metabolism]]s 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 [[homeotherm]]s.<ref>Campbell, N. A., Reece, J. B., et al. (2002). Biology. 6th edition. Benjamin / Cummings Publishing Company.</ref>
==Adaptations in poikilotherms== *Some adaptations are behavioral. Lizards and [[snake]]s bask in the sun in the early morning and late evening, and seek shelter around noon.{{cn|date=March 2025}} *The eggs of the [[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. {{cn|date=March 2025}} *[[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.{{cn|date=March 2025}} * [[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 [[gill]]s. They also have their swimming muscles near the center of their bodies instead of near the surface, which minimises heat loss.{{cn|date=March 2025}} * [[Gigantothermy]] means growing to large size in order to reduce heat loss, as in [[sea turtle]]s and [[Last glacial period|ice-age]] [[Megafauna#Evolution of large body size|megafauna]]. 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.{{cn|date=March 2025}} * [[Camel]]s, 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.<ref>{{cite book |last=Hill |first=Richard |year=2016 |title=Animal Physiology |pages=270 |publisher=Sinauer Associates |place=Sunderland, MA |isbn=978-1605354712}}</ref>
==Ecology== 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.{{Citation needed|date=February 2009}} Such applies even to animals with similar ecological roles such as [[cat]]s and [[snake]]s.
This difference in energy requirement also means that a given food source can support a greater density of poikilothermic animals than homeothermic animals.<ref>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. [https://www.jstor.org/stable/3544877 summary]</ref> 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).{{cn|date=March 2025}}
==In medicine== In medicine, loss of normal thermoregulation is referred to as ''poikilothermia''. This can be seen in [[compartment syndrome]] and with use of [[sedative-hypnotic]]s like [[barbiturate]]s, [[ethanol]], and [[chloral hydrate]].{{Citation needed|date=June 2010}} [[REM sleep]] is considered a poikilothermic state in humans.<ref>{{cite book|title=Sleep Medicine Essentials|year=2009|publisher=Wiley-Blackwell|pages=12|author=Leon Rosenthal|author-link=Physiologic Processes During Sleep|editor=Teofilo Lee-Chiong|chapter=3}}</ref> Poikilothermia is one of the signs of [[acute limb ischemia]].{{citation needed|date=October 2022}}
==Notes== {{reflist|25em}}
==External links== * {{wiktionary-inline}}
[[Category:Animal physiology]] [[Category:Thermoregulation]]