Poikilotherm: Difference between revisions

{{Expert needed|biology|reason=ArtArticle could have a lot more information|date=July 2016}}

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=}}</ref> One of the most important stressors is temperature change, which can lead to alterations in membrane lipid order and can cause protein unfolding and denaturation at elevated temperatures.<ref name=":0" /> It is the opposite of a [[homeotherm]], an animal which maintains [[thermal regulation|thermal]] [[homeostasis]]. While the term in principle can apply to all [[organism]]s, it is generally only applied to animals, and mostly to [[vertebrate]]s. 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|page=429|isbn=0-471-29505-1|author=Milton Hildebrand|author2=G. E. Goslow Jr.|others=Principal ill. Viola Hildebrand.|year=2001|publisher=Wiley|location=New York|title=Analysis of vertebrate structure}}</ref> However some ectotherms remain in temperature-constant environments to the point that they are actually able to maintain a constant internal temperature (i.e.and are considered [[homeotherm]]ic).<ref>{{Cite journal|title=Body size shifts influence effects of increasing temperatures on ectotherm metabolism|journal=Global Ecology and Biogeography}}</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)">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}}</ref><ref name="Sherwin, (2010)">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</ref> and [[sloth]]<ref>{{Cite journal|lastlast1=Britton|firstfirst1=S. W.|last2=Atkinson|first2=W. E.|date=1938|title=Poikilothermism in the Sloth|journal=Journal of Mammalogy|volume=19|issue=1|pages=94|doi=10.2307/1374287|jstor=1374287}}</ref> are some of the rare mammals which are poikilothermic.

The term derives from [[Ancient Greek|Greek]] ''poikilos'' ({{lang|el|ποικίλος}}), meaning "varied," ultimately from a root meaning "dappled" or “painted"painted,”" and ''thermos'' ({{lang|el|θερμός}}), meaning "heat".

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>

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).

In medicine, loss of normal thermoregulation in humans is referred to as "''poikilothermia"''. This iscan usuallybe seen with sedative and hypnotic drugs or in '[[compartment syndrome]]'. and Forwith example,use of [[sedative-hypnotic]]s like [[barbiturate]]s, [[ethanol]], and [[chloral hydrate]] may precipitate this effect.{{Citation needed|date=June 2010}} [[REM sleep]] is also 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}}