Eurytherm

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A eurytherm is an organism, often an endotherm, that can function at a wide range of ambient temperatures. [1] To be considered a eurytherm, all stages of an organism's life cycle must be considered, including juvenile and larval stages. [2] These wide ranges of tolerable temperatures are directly derived from the tolerance of a given eurythermal organism's proteins. [3] Extreme examples of eurytherms include Tardigrades ( Tardigrada ), the desert pupfish (Cyprinodon macularis), and green crabs ( Carcinus maenas ), however, nearly all mammals, including humans, are considered eurytherms. [4] [5] [6] Eurythermy can be an evolutionary advantage: adaptations to cold temperatures, called cold-eurythemy, are seen as essential for the survival of species during ice ages. [7] In addition, the ability to survive in a wide range of temperatures increases a species' ability to inhabit other areas, an advantage for natural selection.

Contents

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. [8] 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.

A boreal forest in Canada. This forest would likely house deciduous conifers. Canon Miles, Yukon, Canada, 2017-08-26, DD 130-132 PAN.jpg
A boreal forest in Canada. This forest would likely house deciduous conifers.

Examples

The distribution of the killer whale (Orcinus orca) shown in blue. This cosmopolitan species occupies nearly every area of the world ocean. Cypron-Range Orcinus orca.svg
The distribution of the killer whale (Orcinus orca) shown in blue. This cosmopolitan species occupies nearly every area of the world ocean.

Advantages over stenotherms

It is thought that adaptations to cold temperatures (cold-eurythermy) in animals, despite the high cost of functional 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 endothermy, eurythermy is considered to be the "missing link" between ectothermy and endothermy. [14] 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 extinctions, [15] 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 reefs. Most species of coral are considered to be stenothermic. [16] 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. [17] [18] 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. [19] 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. [20]

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. [21] 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. [22] Reptiles are ectotherms, and therefore rely upon positive 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. [22] 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. [23]

The green crab is an exceedingly common species of shore crab. Considered an invasive species, the green crab's ability to function in a wide range of water and air temperatures allows it to vary widely in its range. Kleiner Taschenkrebs (Carcinus maenas).jpg
The green crab is an exceedingly common species of shore crab. Considered an invasive species, the green crab's ability to function in a wide range of water and air temperatures allows it to vary widely in its range.

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. [1]

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 cutaneous blood flow, which maintains this temperature despite changes in the external environment. [24] Homo Sapiens ' ability to survive in different ambient temperatures is a key factor in the species success, and one cited reason for why Homo sapiens eventually outcompeted Neanderthals ( Homo neanderthalensis). [25] Humans have two major forms of thermogenesis. The first is shivering, in which a warm-blooded creature produces involuntary contraction of skeletal muscle in order to produce heat. [26] In addition, shivering also signals the body to produce irisin, a hormone that has been shown to convert white fat to brown fat, which is used in non-shivering thermogenesis, the second type of human thermogensis. [27] Non-shivering thermogenesis occurs in the brown fat, which contains the uncoupling protein thermogenin. This protein decreases the proton gradient generated in oxidative phosphorylation during the synthesis of ATP, uncoupling the electron transport in the mitochondrion from the production of chemical energy (ATP). This creation of a gradient across the mitochondrial membrane causes energy to be lost as heat. [28] On the other hand, humans have only one method of cooling themselves, biologically speaking: sweat evaporation. Cutaneous eccrine sweat glands produce sweat, which is made up of mostly water with a small amount of ions. Evaporation of this sweat helps to cool the blood beneath the skin, resulting in a cooling of deep-body temperature.

A Tardigrade is able to enter an anhydrobiotic stage, often called a tun, in order to increase the range of temperatures that it can withstand. Hypsibiusdujardini.jpg
A Tardigrade is able to enter an anhydrobiotic stage, often called a tun, in order to increase the range of temperatures that it can withstand.

While some organisms are eurythermic due to their ability to regulate internal body temperature, like humans, others have wildly different methods of extreme temperature tolerance. Tardigrades are able to enter an anhydrobiotic state, often called a tun, in order to both prevent desiccation and endure extreme temperatures. In this state, tardigrades decrease their bodily water to about 1–3% wt./wt. [5] Although this state allows certain tardigrades to endure temperatures at the extremes of –273° and 150 °C at the extremes, tardigrades in their hydrated state are able to withstand temperatures as low as –196 °C. This displayed extremotolerance has led scientists to speculate that tardigrades could theoretically survive on Mars, where temperatures regularly fluctuate between –123° and 25 °C, as well as even possibly the near absolute zero of interplanetary space. The tardigrade's ability to withstand extremely cold temperatures as a tun is a form of cryptobiosis called cryobiosis. Although the high temperature endurance of tardigrades has been significantly less studied, their cryobiotic response to low temperatures has been well-documented. [29] [30] Tardigrades are able to withstand such cold temperatures not by avoiding freezing using antifreeze proteins as a freeze avoidance organism would, but rather by tolerating ice formation in the extracellular body water, activated by ice nucleating proteins.

In addition to other organisms, plants (Plantae) can be either stenothermic or eurythermic. Plants inhabiting the boreal and polar 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. [31] This is in direct contrast to plants that typically inhabit more tropical or montane regions, where plants may have purely tolerable range between only about 10° and 25 °C, such as the banyan tree. [31]

The common carp (Cyprinus carpio) has shown higher protein synthesis rates at high temperatures. Common carp.jpg
The common carp (Cyprinus carpio) has shown higher protein synthesis rates at high temperatures.

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. [3] [32] Eurythermal species also have shown adaptations in protein synthesis rates compared to non-eurythermal similar species. Rainbow trout (Salmo gairdneri ) 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 (Cyprinus carpio ) have shown significantly higher protein synthesis rates after acclimating to higher water temperatures (25 °C) than after acclimating to lower water temperatures (10 °C). [33] 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, glutamate, 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.

Related Research Articles

<span class="mw-page-title-main">Warm-blooded</span> Animal species that can maintain a body temperature higher than their environment

Warm-blooded is an informal term referring to animal species whose bodies maintain a temperature higher than that of their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. Other species have various degrees of thermoregulation.

<span class="mw-page-title-main">Hibernation</span> Physiological state of dormant inactivity in order to pass the winter season

Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most commonly occurs during winter months.

<span class="mw-page-title-main">Homeothermy</span> Thermoregulation that maintains a stable internal body temperature regardless of external influence

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 environment. Homeothermy is one of the three types of thermoregulation in warm-blooded animal species. Homeothermy's opposite is poikilothermy. A poikilotherm is an organism that does not maintain a fixed internal temperature but rather fluctuates based on their environment and physical behaviour.

A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from 20 to 45 °C. The optimum growth temperature for these organisms is 37°C. The term is mainly applied to microorganisms. Organisms that prefer extreme environments are known as extremophiles. Mesophiles have diverse classifications, belonging to two domains: Bacteria, Archaea, and to kingdom Fungi of domain Eucarya. Mesophiles belonging to the domain Bacteria can either be gram-positive or gram-negative. Oxygen requirements for mesophiles can be aerobic or anaerobic. There are three basic shapes of mesophiles: coccus, bacillus, and spiral.

<span class="mw-page-title-main">Endotherm</span> Organism that maintains body temperature largely by heat from internal bodily functions

An endotherm is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production. Examples include special-function muscular exertion such as shivering, and uncoupled oxidative metabolism, such as within brown adipose tissue.

<span class="mw-page-title-main">Thermoregulation</span> Ability of an organism to keep its body temperature within certain boundaries

Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature as its own body temperature, thus avoiding the need for internal thermoregulation. The internal thermoregulation process is one aspect of homeostasis: a state of dynamic stability in an organism's internal conditions, maintained far from thermal equilibrium with its environment. If the body is unable to maintain a normal temperature and it increases significantly above normal, a condition known as hyperthermia occurs. Humans may also experience lethal hyperthermia when the wet bulb temperature is sustained above 35 °C (95 °F) for six hours. Work in 2022 established by experiment that a wet-bulb temperature exceeding 30.55°C caused uncompensable heat stress in young, healthy adult humans. The opposite condition, when body temperature decreases below normal levels, is known as hypothermia. It results when the homeostatic control mechanisms of heat within the body malfunction, causing the body to lose heat faster than producing it. Normal body temperature is around 37°C(98.6°F), and hypothermia sets in when the core body temperature gets lower than 35 °C (95 °F). Usually caused by prolonged exposure to cold temperatures, hypothermia is usually treated by methods that attempt to raise the body temperature back to a normal range. It was not until the introduction of thermometers that any exact data on the temperature of animals could be obtained. It was then found that local differences were present, since heat production and heat loss vary considerably in different parts of the body, although the circulation of the blood tends to bring about a mean temperature of the internal parts. Hence it is important to identify the parts of the body that most closely reflect the temperature of the internal organs. Also, for such results to be comparable, the measurements must be conducted under comparable conditions. The rectum has traditionally been considered to reflect most accurately the temperature of internal parts, or in some cases of sex or species, the vagina, uterus or bladder.

<span class="mw-page-title-main">Ectotherm</span> Organism where internal heating sources are small or negligible

An ectotherm, more commonly referred to as a "cold-bloodedanimal", is an animal in which internal physiological sources of heat are of relatively small or of quite negligible importance in controlling body temperature. Such organisms rely on environmental heat sources, which permit them to operate at very economical metabolic rates.

Thermogenesis is the process of heat production in organisms. It occurs in all warm-blooded animals, and also in a few species of thermogenic plants such as the Eastern skunk cabbage, the Voodoo lily, and the giant water lilies of the genus Victoria. The lodgepole pine dwarf mistletoe, Arceuthobium americanum, disperses its seeds explosively through thermogenesis.

<span class="mw-page-title-main">Cryptobiosis</span> Metabolic state of life

Cryptobiosis or anabiosis is a metabolic state in extremophilic organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop, preventing reproduction, development, and repair. When environmental conditions return to being hospitable, the organism will return to its metabolic state of life as it was prior to cryptobiosis.

<span class="mw-page-title-main">Desert ecology</span> The study of interactions between both biotic and abiotic components of desert environments

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<span class="mw-page-title-main">Giant Pacific octopus</span> Species of cephalopod

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The physiology of dinosaurs has historically been a controversial subject, particularly their thermoregulation. Recently, many new lines of evidence have been brought to bear on dinosaur physiology generally, including not only metabolic systems and thermoregulation, but on respiratory and cardiovascular systems as well.

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<span class="mw-page-title-main">Tardigrade</span> Phylum of microscopic animals, also known as water bears

Tardigrades, known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär. In 1777, the Italian biologist Lazzaro Spallanzani named them Tardigrada, which means "slow steppers".

<span class="mw-page-title-main">Kleptothermy</span> Form of thermoregulation in which an animal shares in the heat production of another

In biology, kleptothermy is any form of thermoregulation by which an animal shares in the metabolic thermogenesis of another animal. It may or may not be reciprocal, and occurs in both endotherms and ectotherms. One of its forms is huddling. However, kleptothermy can happen between different species that share the same habitat, and can also happen in pre-hatching life where embryos are able to detect thermal changes in the environment.

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<span class="mw-page-title-main">Mesotherm</span> Type of animal that produces metabolic heat, but has no specific body temperature

A mesotherm is a type of animal with a thermoregulatory strategy intermediate to cold-blooded ectotherms and warm-blooded endotherms.

Cold and heat adaptations in humans are a part of the broad adaptability of Homo sapiens. Adaptations in humans can be physiological, genetic, or cultural, which allow people to live in a wide variety of climates. There has been a great deal of research done on developmental adjustment, acclimatization, and cultural practices, but less research on genetic adaptations to colder and hotter temperatures.

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