Kleptothermy

Thermoregulation in animals
Ectotherm Endotherm Mesotherm Poikilotherm Homeothermy Heterothermy Stenotherm Eurytherm Thermolabile Thermostability Gigantothermy Kleptothermy Bradymetabolism Tachymetabolism Thermogenesis
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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.^[1] 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.

This process requires two major conditions: the thermal heterogeneity created by the presence of a warm organism in a cool environment in addition to the use of that heterogeneity by another animal to maintain body temperatures at higher (and more stable) levels than would be possible elsewhere in the local area.

Huddling confers higher and more constant body temperatures than solitary resting.[3] Some species of ectotherms including lizards^[4] and snakes, such as boa constrictors^[5] and tiger snakes,^[6] increase their effective mass by clustering tightly together. It is also widespread amongst gregarious endotherms such as bats^[7] and birds (such as the mousebird^[8] and emperor penguin^[9]) where it allows the sharing of body heat, particularly among juveniles.

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On the other hand, huddling allows emperor penguins (Aptenodytes forsteri) to save energy, maintain a high body temperature and sustain their breeding fast during the Antarctic winter.^[12] This huddling behaviour raises the ambient temperature that these penguins are exposed to above 0 °C (at average external temperatures of -17 °C).^[12] As a consequence of tight huddles, ambient temperatures can be above 20 °C and can increase up to 37.5 °C, close to birds' body temperature.^[12] Therefore, this complex social behaviour is what enables all breeders to get an equal and normal access to an environment which allows them to save energy and successfully incubate their eggs during the Antarctic winter.^[12]

Habitat sharing

Many ectotherms exploit the heat produced by endotherms by sharing their nests and burrows. For example, mammal burrows are used by geckos and seabird burrows by Australian tiger snakes and New Zealand tuatara.^[13] Termites create high and regulated temperatures in their mounds, and this is exploited by some species of lizards, snakes and crocodiles.^[14][15]

Research has shown such kleptothermy can be advantageous in cases such as the blue-lipped sea krait (

Research done on embryos of Chinese softshell turtles (Pelodiscus sinensis) falsify the assumption that behavioural thermoregulation is possible only for post-hatching stages of the reptile life history.^[17] Remarkably, even undeveloped and tiny embryos were able to detect thermal differentials within the egg and move to exploit that small-scale heterogeneity.^[17] Research has shown that this behaviour exhibited by reptile embryos may well enhance offspring fitness where movements of these embryos enabled them to maximize heat gain from their surroundings and thus increase their body temperatures.^[17] This in turn leads to a variation in the embryonic development rate and the incubation period as well.^[17] This could benefit the embryos in which a warmer incubation increases developmental rate and therefore accelerating the hatching process.^[17]

On the other hand, decreased incubation periods also may minimize the embryo's exposure to risks of nest predation or lethal extremes thermal conditions where embryos move to cooler regions of the egg during periods of dangerously high temperatures.^[17]

In addition, embryonic thermoregulation could enhance hatching fitness via modifications to a range of phenotypic traits where embryos with minimal temperature differences hatch at the same time decreasing the individuals' risk of predation.^[17] Therefore, the developmental rates of embryos of reptiles are not passive consequences of maternally enforced decisions about the temperatures that the embryo will experience before hatching.^[17] Instead, the embryo's behaviour and physiology combine, allowing the smallest embryos to control aspects of their own pre-hatching environment showing that the embryo is not simply a work in progress, but is a functioning organism with surprisingly sophisticated and effective behaviours.^[17]

Evolution

Ectotherms and endotherms undergo different evolutionary perspectives where mammals and birds thermoregulate far more precisely than ectotherms.^[18] A major benefit of precise thermoregulation is the ability to enhance performance through thermal specialization.^[18] Therefore, mammals and birds are assumed to have evolved relatively narrow performance breadths.^[18] Thus, the heterothermy of these endotherms would lead to losses of performance during certain periods and therefore genetic variation in thermosensitivity would enable the evolution of thermal generalists in more heterothermic species.^[18] The physiologies of the endotherms allows them to adapt within the constraints imposed by genetics, development, and physics.^[18]

On the other side, the mechanisms for thermoregulation did not evolve separately, but rather in connection with other functions.

Endothermy in vertebrates evolved along separate, but parallel lines from different groups of reptilian ancestors.[20] The advantages of endothermy are manifested in the ability to occupy thermal areas that exclude many ectothermic vertebrates, a high degree of thermal independence from environmental temperature, high muscular power output and sustained levels of activity.^[20] Endothermy, however, is energetically very expensive and requires a great deal of food, compared with ectotherms in order to support high metabolic rates.^[20]

See also

• Rat king

References