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Heterothermy or heterothermia (from
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
ἕτερος ''heteros'' "other" and θέρμη ''thermē'' "heat") is a physiological term for
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s that vary between self-regulating their body temperature, and allowing the surrounding environment to affect it. In other words, they exhibit characteristics of both
poikilothermy A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
and
homeothermy Homeothermy, homothermy or homoiothermy is thermoregulation Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system ...
.


Definition

Heterothermic animals are those that can switch between
poikilotherm A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
ic and
homeotherm Homeothermy, homothermy or homoiothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This internal body temperature is often, though not necessarily, higher than the immediate environmen ...
ic strategies. These changes in strategies typically occur on a daily basis or on an annual basis. More often than not, it is used as a way to dissociate the fluctuating metabolic rates seen in some small mammals and birds (e.g.
bat Bats are mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meanin ...

bat
s and
hummingbirds Hummingbirds are Bird, birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With about 360 species, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropi ...
), from those of traditional cold blooded animals. In many
bat Bats are mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meanin ...

bat
species, body temperature and metabolic rate are elevated only during activity. When at rest, these animals reduce their
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
s drastically, which results in their body temperature dropping to that of the surrounding environment. This makes them
homeothermic Homeothermy, homothermy or homoiothermy is thermoregulation Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system ...
when active, and
poikilothermic A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...
when at rest. This phenomenon has been termed 'daily
torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμό ...
' and was intensively studied in the Djungarian hamster. During the
hibernation Hibernation is a state of minimal activity and metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological ...

hibernation
season, this animal shows strongly reduced metabolism each day during the rest phase while it reverts to
endotherm An endotherm (from Ancient Greek, Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily ...
ic metabolism during its active phase, leading to normal euthermic body temperatures (around 38 °C). Larger mammals (e.g.
ground squirrel The ground squirrels are members of the squirrel family of rodents (Sciuridae), which generally live on or in the ground, rather than trees. The term is most often used for the medium-sized ground squirrels, as the larger ones are more commonly kno ...

ground squirrel
s) and
bat Bats are mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meanin ...

bat
s show multi-day torpor bouts during hibernation (up to several weeks) in winter. During these multi-day torpor bouts, body temperature drops to ~1 °C above ambient temperature and metabolism may drop to about 1% of the normal endothermic metabolic rate. Even in these deep hibernators, the long periods of torpor is interrupted by bouts of endothermic metabolism, called arousals (typically lasting between 4–20 hours). These metabolic arousals cause body temperature to return to euthermic levels 35-37 °C. Most of the energy spent during hibernation is spent in arousals (70-80%), but their function remains unresolved. Shallow hibernation patterns without arousals have been described in large mammals (like the black bear,) or under special environmental circumstances.


Regional heterothermy

Regional heterothermy describes organisms that are able to maintain different temperature "zones" in different regions of the body. This usually occurs in the limbs, and is made possible through the use of counter-current heat exchangers, such as the
rete mirabile A rete mirabile (Latin for "wonderful net"; plural retia mirabilia) is a complex of artery, arteries and veins lying very close to each other, found in some vertebrates, mainly warm-blooded ones. The rete mirabile utilizes countercurrent blood flo ...
found in tuna and certain birds. These exchangers equalize the temperature between hot arterial blood going out to the extremities and cold venous blood coming back, thus reducing heat loss. Penguins and many arctic
birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

birds
use these exchangers to keep their feet at roughly the same temperature as the surrounding ice. This keeps the
birds Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

birds
from getting stuck on an ice sheet. Other animals, like the
leatherback sea turtle The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtle Turtles are an of s known as Testudines, characterized by a developed ma ...
, use the heat exchangers to gather, and retain heat generated by their muscular flippers. There are even some
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
s which possess this mechanism (see insect thermoregulation), the best-known example being
bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only Extant taxon, extant group in the tribe Bombini, though a few extinct ...

bumblebee
s, which exhibit counter-current heat exchange at the point of constriction between the
mesosoma The mesosoma is the middle part of the body, or tagma (biology), tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the arthropod leg, legs, and, in the case of winged insects, th ...
("thorax") and
metasoma The metasoma is the posterior part of the body, or tagma (biology), tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory sys ...
("abdomen"); heat is retained in the thorax and lost from the abdomen. Heinrich, B. 1976. 'Heat exchange in relation to blood flow between thorax and abdomen in bumblebees', Journal of Experimental Biology 64, 561–585 Using a very similar mechanism, the internal temperature of a
honeybee A honey bee (also spelled honeybee) is a eusocial Eusociality (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in So ...

honeybee
's thorax can exceed 45 °C while in flight.


See also

* Mesotherm *
Poikilotherm A poikilotherm () is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellula ...


References

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External links


Thermobiology of bats
Animal physiology Thermoregulation sv:Heteroterm