関: poikilothermic animal

WordNet

an animal whose body temperature varies with the temperature of its surroundings; any animal except birds and mammals (同)ectotherm
of animals except birds and mammals; having body temperature that varies with the environment (同)poikilothermous, heterothermic, ectothermic

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/05/05 19:13:20」(JST)

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Look up poikilotherm in Wiktionary, the free dictionary.

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

A poikilotherm is an organism whose internal temperature varies considerably. It is the opposite of a homeotherm, an organism which maintains 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]

Etymology

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

Physiology

Sustained power 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 a half to a tenth 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.

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]} 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.

Poikilotherms succeed in some habitats, such as islands and hot deserts, or distinct bioregions (such as the small bioregions of the Amazon basin). These biomes often do not have enough food to support a viable breeding population of homeothermic animals. In these habitats, poikilotherms such as large lizards, crabs and frogs supplant homeotherms such as birds and mammals.

In medicine

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

Notes

^ Milton Hildebrand; G. E. Goslow, Jr. Principal ill. Viola Hildebrand. (2001). Analysis of vertebrate structure. New York: Wiley. p. 429. ISBN 0-471-29505-1.
^ 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
^ 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
^ (Greek) Triantafyllidis Online Lexicon, ποικιλόθερμος. Retrieved on 2007-01-12.
^ Cavalier-Smith, T. "Coevolution of vertebrate genome, cell, and nuclear sizes". Symposium on the Evolution of Terrestrial Vertebrates: 51–86.
^ Ryan Gregory, T. (1 January 2002). "Genome size and developmental complexity". Genetica 115 (1): 131–146. doi:10.1023/A:1016032400147. |accessdate= requires |url= (help)
^ Willmer, P., Stone, G., & Johnston, I. A. (2000): Environmental physiology of animals. Blackwell Science, London. 644 pages, ISBN 0-632-03517-X.
^ Campbell, N. A., Reece, J. B., et al. (2002). Biology. 6th edition. Benjamin / Cummings Publishing Company.
^ 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
^ Leon Rosenthal (2009). "3". In Teofilo Lee-Chiong. Sleep Medicine Essentials. Wiley-Blackwell. p. 12.

English Journal

Dynamic response of RNA editing to temperature in Drosophila.

Rieder LE, Savva YA, Reyna MA, Chang YJ, Dorsky JS, Rezaei A, Reenan RA.
BMC biology.BMC Biol.2015 Jan 3;13:1. doi: 10.1186/s12915-014-0111-3.
BACKGROUND: Adenosine-to-inosine RNA editing is a highly conserved process that post-transcriptionally modifies mRNA, generating proteomic diversity, particularly within the nervous system of metazoans. Transcripts encoding proteins involved in neurotransmission predominate as targets of such modifi
PMID 25555396

Critical windows in embryonic development: Shifting incubation temperatures alter heart rate and oxygen consumption of Lake Whitefish (Coregonus clupeaformis) embryos and hatchlings.

Eme J1, Mueller CA2, Manzon RG3, Somers CM4, Boreham DR5, Wilson JY6.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology.Comp Biochem Physiol A Mol Integr Physiol.2015 Jan;179:71-80. doi: 10.1016/j.cbpa.2014.09.005. Epub 2014 Sep 16.
Critical windows are periods of developmental susceptibility when the phenotype of an embryonic, juvenile or adult animal may be vulnerable to environmental fluctuations. Temperature has pervasive effects on poikilotherm physiology, and embryos are especially vulnerable to temperature shifts. To ide
PMID 25236178

First Demonstration of Antigen Induced Cytokine Expression by CD4-1+ Lymphocytes in a Poikilotherm: Studies in Zebrafish (Danio rerio).

Yoon S1, Mitra S1, Wyse C1, Alnabulsi A2, Zou J1, Weerdenburg EM3, M van der Sar A3, Wang D4, Secombes CJ1, Bird S1.
PloS one.PLoS One.2015 Jun 17;10(6):e0126378. doi: 10.1371/journal.pone.0126378. eCollection 2015.
Adaptive immunity in homeotherms depends greatly on CD4+ Th cells which release cytokines in response to specific antigen stimulation. Whilst bony fish and poikilothermic tetrapods possess cells that express TcR and CD4-related genes (that exist in two forms in teleost fish; termed CD4-1 and CD4-2),
PMID 26083432

Japanese Journal

Temperature-dependent tonic contraction of smooth muscle in Antarctic fishes Notothenia neglecta and Chaenocephalus aceratus - Role of calcium ions and responses to acetylcholine

Bastos-Ramos Wilma Pereira,Hoshino Katsumasa,Bacila Metry
Polar bioscience 13, 74-86, 2000-02
… The temperature-related tonic contraction is not a general event in poikilotherm animals, since it did not occur in the Bufo marinus intestinal smooth muscle, in similar experiments carried out as a control, in a tropical environment. …
NAID 110000035869

5. 変温動物はなぜ低温でも繁殖できるか : 生殖腺刺激ホルモン受容体の研究より(セミナー「低温と生物」)

窪川かおる
凍結及び乾燥研究会会誌 38, 117-121, 1992-10-20
Effects of temperature on the kinetic and equilibrium parameters of the binding reaction of a gonadotropic hormone (follicle stimulating hormone, FSH) to its receptor in both homeothermic and poikilot …
NAID 110007368519

チリのギンザケ病魚から分離されたリッケチア様生物〔英文〕

Fryer J.L. [他],LANNAN C.N.,GARCES L.H.,LARENAS J.J.,SMITH P.A.
魚病研究 25(2), 107-114, 1990
… On the basis of available information, we suggest this organism is a member of the order Rickettsiales and represents the first isolation of a member of this group from an aquatic poikilotherm. …
NAID 130000857878