The temperature-size rule denotes the plastic response (i.e. phenotypic plasticity) of organismal body size to environmental temperature variation. [1] [2] Organisms exhibiting a plastic response are capable of allowing their body size to fluctuate with environmental temperature. First coined by David Atkinson in 1996, [3] it is considered to be a unique case of Bergmann's rule [1] that has been observed in plants, animals, birds, and a wide variety of ectotherms. [2] [4] [5] [6] [7] Although exceptions to the temperature-size rule exist, recognition of this widespread "rule" has amassed efforts to understand the physiological mechanisms (via possible tradeoffs) underlying growth and body size variation in differing environmental temperatures. [2] [8]
In 1847, Carl Bergmann published his observations that endothermic body size (i.e. mammals) increased with increasing latitude, commonly known as Bergmann's rule. [9] His rule postulated that selection favored within species individuals with larger body sizes in cooler temperatures because the total heat loss would be diminished through lower surface area to volume ratios. [8] However, ectothermic individuals thermoregulate and allow their internal body temperature to fluctuate with environmental temperature whereas endotherms maintain a constant internal body temperature. This creates an inaccurate description of observed body size variation in ectotherms since they routinely allow evaporative heat loss and do not maintain constant internal temperatures. [8] [10] Despite this, ectotherms have largely been observed to still exhibit larger body sizes in colder environments.
Ray (1960) originally examined body sizes in several species of ectotherms and discovered that around 80% of them exhibited larger body sizes in lower temperatures. [11] A few decades later, Atkinson (1994) performed a similar review of temperature effects on body size in ectotherms. His study, which included 92 species of ectotherms ranging from animals and plants to protists and bacteria, concluded that a reduction in temperature resulted in an increase in organism size in 83.5% of cases. [11] [12] [13] Atkinson's findings provided support for Ray's published works that ectotherms have an observable trend in body size when temperature is the primary environmental variable. The results of his study prompted him to name the increase in ectothermic body size in colder environments as the temperature-size rule.
Life history models highlighting optimal growth patterns suggest that individuals assess the environment for potential resources and other proximate factors and mature at a body size that yields the greatest reproductive success, or highest percentage of offspring surviving to reach reproductive maturity. [14]
Environmental temperature is one of the most important proximate factors affecting ectotherm body size because of their need to thermoregulate. Individuals that have been observed to follow the temperature-size rule have slower growth rates in colder environments, yet they enter a period of prolonged growth that yields larger adult body sizes. [3] [15] [16] One proposed explanation for this involves a trade-off in life history traits. Ectotherms experience longer daily and seasonal activity times in warmer climates versus cooler climates, however, the increase in daily activity time is accompanied by higher infant and adult mortality rates due to predation. [16] [17] Under these environmental conditions, some individuals occupying these warmer climate environments will mature at smaller body sizes and undergo a shift in energy allocation of all acquired energy resources to reproduction. [18] [19] [20] In doing so, these individuals sacrifice growth to larger adult body sizes to ensure reproductive success, even if the trade-off results in smaller offspring that have increased mortality rates. [20]
Ectotherms occupying colder environments, such as mountain ranges or other areas of higher elevation, have been observed to invest in reproduction at larger adult body sizes due to a prolonged growth period. These populations of ectotherms are characterized as having smaller clutches of larger eggs, favoring a greater reproductive investment per egg and enhances offspring survival rates. [21] Individuals occupying warmer environments experience a trade-off between body size and overall reproductive success that many individuals occupying colder environments do not, hence, prolonging growth to yield greater reproductive success in colder environments could potentially be an underlying mechanism for why a large percentage of ectotherms exhibit greater body sizes in colder environments. However, a sufficient explanation for this observable pattern has yet to be produced. [14]
The supporting evidence and the exceptions to the temperature-size rule listed above are only a few of the potential supporting/opposing evidence available for the temperature-size rule. Each was provided to support the claim that patterns of body size observed in variable environments are not 100% predictable and more research is required to identify and understand all of the mechanisms responsible.
Centrarchidae, better known as sunfishes, is a family of freshwater ray-finned fish belonging to the order Perciformes, native only to North America. There are eight universally included genera within the centrarchid family: Lepomis, Micropterus, Pomoxis (crappies), Enneacanthus, Centrarchus, Archoplites, Ambloplites, and Acantharchus. A genetic study in 2012 suggests that the highly distinct pygmy sunfishes of the genus Elassoma are also centrarchids.
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.
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.
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.
Bergmann's rule is an ecogeographical rule that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer regions. Bergmann's rule only describes the overall size of the animals, but does not include body parts like Allen's rule does.
The viviparous lizard, or common lizard, is a Eurasian lizard. It lives farther north than any other species of non-marine reptile, and is named for the fact that it is viviparous, meaning it gives birth to live young. Both "Zootoca" and "vivipara" mean "live birth," in Greek and Latin respectively. It was called Lacerta vivipara until the genus Lacerta was split into nine genera in 2007 by Arnold, Arribas & Carranza.
Allen's rule is an ecogeographical rule formulated by Joel Asaph Allen in 1877, broadly stating that animals adapted to cold climates have shorter and thicker limbs and bodily appendages than animals adapted to warm climates. More specifically, it states that the body surface-area-to-volume ratio for homeothermic animals varies with the average temperature of the habitat to which they are adapted.
Darwin’s frog, also called the Southern Darwin's frog, is a species of Chilean/Argentinian frog of the family Rhinodermatidae. It was discovered by Charles Darwin during his voyage on HMS Beagle. on a trip to Chile. In 1841, French zoologist André Marie Constant Duméril and his assistant Gabriel Bibron described and named Darwin's frog. The diet of R. darwinii consists mostly of herbivore invertebrates. R. darwinii is currently classified as an endangered species by the International Union for Conservation of Nature.
The common side-blotched lizard is a species of side-blotched lizard in the family Phrynosomatidae. The species is native to dry regions of the western United States and northern Mexico. It is notable for having a unique form of polymorphism wherein each of the three different male morphs utilizes a different strategy in acquiring mates. The three morphs compete against each other following a pattern of rock paper scissors, where one morph has advantages over another but is outcompeted by the third.
Urosaurus ornatus, commonly known as the ornate tree lizard, is a species of lizard in the family Phrynosomatidae. The species is native to the southwestern United States and northwestern Mexico. The species, which was formerly called simply the "tree lizard", has been used to study physiological changes during the fight-or-flight response as related to stress and aggressive competition. Its life history and costs of reproduction have been documented in field populations in New Mexico and Arizona. This species has been fairly well studied because of its interesting variation in throat color in males that can correlate with different reproductive strategies,
The sagebrush lizard or sagebrush swift is a common species of phrynosomatid lizard found at mid to high altitudes in the western United States of America. It belongs to the genus Sceloporus in the Phrynosomatidae family of reptiles. Named after the sagebrush plants near which it is commonly found, the sagebrush lizard has keeled and spiny scales running along its dorsal surface.
Climatic adaptation refers to adaptations of an organism that are triggered due to the patterns of variation of abiotic factors that determine a specific climate. Annual means, seasonal variation and daily patterns of abiotic factors are properties of a climate where organisms can be adapted to. Changes in behavior, physical structure, internal mechanisms and metabolism are forms of adaptation that is caused by climate properties. Organisms of the same species that occur in different climates can be compared to determine which adaptations are due to climate and which are influenced majorly by other factors. Climatic adaptations limits to adaptations that have been established, characterizing species that live within the specific climate. It is different from climate change adaptations which refers to the ability to adapt to gradual changes of a climate. Once a climate has changed, the climate change adaptation that led to the survival of the specific organisms as a species can be seen as a climatic adaptation. Climatic adaptation is constrained by the genetic variability of the species in question.
The Argentine black and white tegu, also known as the Argentine giant tegu, the black and white tegu, or the huge tegu, is a species of lizard in the family Teiidae. The species is the largest of the "tegu lizards". It is an omnivorous species which inhabits the tropical rain forests, savannas and semi-deserts of eastern and central South America.
In biology, a cline is a measurable gradient in a single characteristic of a species across its geographical range. First coined by Julian Huxley in 1938, the cline usually has a genetic, or phenotypic character. Clines can show smooth, continuous gradation in a character, or they may show more abrupt changes in the trait from one geographic region to the next.
The eastern three-lined skink, also known commonly as the bold-striped cool-skink, is a species of skink, a lizard in the family Scincidae. The species is endemic to Australia. A. duperreyi has been extensively studied in the context of understanding the evolution of learning, viviparity in lizards, and temperature- and genetic-sex determination. A. duperreyi is classified as a species of "Least Concern" by the IUCN.
In zoology, deep-sea gigantism or abyssal gigantism is the tendency for species of invertebrates and other deep-sea dwelling animals to be larger than their shallower-water relatives across a large taxonomic range. Proposed explanations for this type of gigantism include colder temperature, food scarcity, reduced predation pressure and increased dissolved oxygen concentrations in the deep sea. The inaccessibility of abyssal habitats has hindered the study of this topic.
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.
A biological rule or biological law is a generalized law, principle, or rule of thumb formulated to describe patterns observed in living organisms. Biological rules and laws are often developed as succinct, broadly applicable ways to explain complex phenomena or salient observations about the ecology and biogeographical distributions of plant and animal species around the world, though they have been proposed for or extended to all types of organisms. Many of these regularities of ecology and biogeography are named after the biologists who first described them.
Countergradient variation is a type of phenotypic plasticity that occurs when the phenotypic variation determined by a biological population's genetic components opposes the phenotypic variation caused by an environmental gradient. This can cause different populations of the same organism to display similar phenotypes regardless of their underlying genetics and differences in their environments.
Thermal ecology is the study of the interactions between temperature and organisms. Such interactions include the effects of temperature on an organism's physiology, behavioral patterns, and relationship with its environment. While being warmer is usually associated with greater fitness, maintaining this level of heat costs a significant amount of energy. Organisms will make various trade-offs so that they can continue to operate at their preferred temperatures and optimize metabolic functions. With the emergence of climate change scientists are investigating how species will be affected and what changes they will undergo in response.