A eurytherm is an organism, often an endotherm, that can function at a wide range of ambient temperatures.
Eurythermy is an aspect of thermoregulation in organisms. It is in contrast with the idea of stenothermic organisms, which can only operate within a relatively narrow range of ambient temperatures.[Hill R, Wyse G, Anderson A. Animal Physiology. 2004. Sinaur Associates, Inc.] Through a wide variety of thermal coping mechanisms, eurythermic organisms can either provide or expel heat for themselves in order to survive in cold or hot, respectively, or otherwise prepare themselves for extreme temperatures. Certain species of eurytherm have been shown to have unique protein synthesis processes that differentiate them from relatively stenothermic, but otherwise similar, species.
Examples
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Tardigrades, known for their ability to survive in nearly any environment, are extreme examples of eurytherms. Certain species of tardigrade, including Mi. tardigradum, are able to withstand and survive temperatures ranging from –273 °C (near absolute zero) to 150 °C in their Anhydrobiosis state.
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The desert pupfish, a rare bony fish that occupies places like the Colorado River Delta in Baja California, small ponds in Sonora, and drainage sites near the Salton Sea in California, can function in waters ranging from 8º to 42 °C.
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The green crab is a common species of Littoral zone crab with a range that extends from Iceland and Central Norway in the north to South Africa and Victoria, Australia in the south, including more temperate regions like Maghreb in between.
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Boreal deciduous Pinophyta (genus Larch) are the primary plants occupying the Taiga of Siberia and North America. Although they are conifers, they are deciduous, and therefore lose their needles in Autumn. Species like the black spruce, or tamarack ( Larix laricina) occupy wide swaths of land ranging from Indiana in the south, well into the arctic circle in Northern Alaska, Canada, and Siberia in the north.
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Killer whales ( Killer whale) are found at nearly every latitude on earth.
Advantages over stenotherms
It is thought that adaptations to cold temperatures (cold-eurythermy) in animals, despite the high cost of
Adaptation, has allowed for mobility and agility. This cold eurythermy is also viewed as a near necessity for survival of the evolutionary crises, including ice ages, that occur with relative frequency over the evolutionary timescale. Due to its ability to provide the excess energy and aerobic scope required for
, eurythermy is considered to be the "missing link" between
and endothermy.
The green crab's success demonstrates one example of eurythermic advantage. Although
invasive species are typically considered to be detrimental to the environment in which they are introduced, and even considered to be a leading cause of animal
,
the ability of an animal to thrive in various environmental conditions is a form of evolutionary fitness, and therefore is typically a characteristic of successful species. A species' relative eurythermality is one of the main factors in its ability to survive in different conditions. One example of eurythermic advantage can be seen in the failure of many of the world's
Coral reef Most species of coral are considered to be stenothermic.
The worldwide increase in oceanic temperatures has caused many coral reefs to begin bleaching and dying because the coral have begun to expel the
zooxanthellae algae that live in their tissues and provide them with their food and color.
This bleaching has resulted in a 50% mortality rate in observed corals in the waters off of Cape York in Northeastern
Australia, and a 12% bleaching rate in observed reefs throughout the world.
Although regulators, especially endotherms, expend a significantly higher proportion of energy per unit of mass, the advantages of endothermy, particularly endogenous thermogenesis, have proven significant enough for selection.
Thermal coping mechanisms
The ability to maintain
homeostasis at varying temperatures is the most important characteristic in defining an endothermic eurytherm, whereas other, thermoconforming eurytherms like tardigrades are simply able to endure significant shifts in their internal body temperature that occur with ambient temperature changes.
Eurythermic animals can be either conformers or regulators, meaning that their internal physiology can either vary with the external environment or maintain consistency regardless of the external environment, respectively. It is important to note that endotherms do not solely rely on internal thermogenesis for all parts of homeostasis or comfort; in fact, in many ways, they are equally as reliant upon behavior to regulate body temperature as ectotherms are.
Reptiles are ectotherms, and therefore rely upon
Thermotaxis, basking (heliothermy), burrowing, and crowding with members of their species in order to regulate their body temperature within a narrow range and even to produce fevers to fight infection.
Similarly, humans rely upon clothing, housing, air conditioning, and drinking to achieve the same goals, although humans are not considered indicative of endotherms on the whole.
The sustained supply of oxygen to body tissues determines the body temperature range of an organism. Eurytherms that live in environments with large temperature changes adapt to higher temperatures through a variety of methods. In green crabs, the process of initial warming results in an increase of oxygen consumption and heart rate, accompanied by a decrease in
stroke volume and
haemolymph oxygen
partial pressure. As this warming continues, dissolved oxygen levels decrease below the threshold for full haemocyanin oxygen saturation. This heating then progressively releases
haemocyanin-bound oxygen, saving energy in oxygen transport and resulting in an associated leveling off of
metabolic rate.
Key to maintaining homeostasis, individual thermoregulation is the ability to maintain internal body temperature in humans, the most recognizable eurytherm. In humans, deep-body temperature is regulated by Human skin Hemodynamics, which maintains this temperature despite changes in the external environment.
In addition to other organisms, plants () can be either stenothermic or eurythermic. Plants inhabiting the boreal and Polar climate climates generally tend to be cold-eurythermic, enduring temperatures as cold as –85°, and as warm as at least 20 °C, such as boreal deciduous conifers.
Eurythermal protein adaptation
The tolerance for extreme body temperatures in a given eurythermic organism is largely due to an increased temperature tolerance by the respective organism's homologous proteins. In particular, the proteins of a warm-adapted species may be inherently more eurythermal than a cold-adapted species, with warm-adapted species' proteins withstanding higher temperatures before beginning to denature, therefore avoiding possible cell death.
Eurythermal species also have shown adaptations in protein synthesis rates compared to non-eurythermal similar species. Rainbow trout
Rainbow trout) have shown constant protein synthesis rates
over temperatures ranging from 5° to 20 °C, after acclimating to any temperature in this range for 1 month. In contrast, carp
Common carp ) have shown significantly higher protein synthesis rates after acclimating to higher water temperatures (25 °C) than after acclimating to lower water temperatures (10 °C).
This type of experiment is common throughout fish. A similar example is given by the Senegalese sole (
Solea senegalensis), which, when acclimated to temperatures of 26 °C, produced a significantly higher amount of
taurine,
Glutamic acid, GABA and
glycine compared to acclimation to 12 °C. This may mean that the aforementioned compounds aid in antioxidant defense, osmoregulatory processes, or energetic purposes at these temperatures.
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