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Aestivation ( la, aestas (summer); also spelled estivation in
American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances ...
) is a state of animal
dormancy Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be c ...
, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a lowered
metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cel ...
rate, that is entered in response to high temperatures and arid conditions. It takes place during times of heat and dryness, the hot dry season, which are often the summer months. Invertebrate and vertebrate animals are known to enter this state to avoid damage from high temperatures and the risk of
desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...
. Both terrestrial and aquatic animals undergo aestivation. Fossil records suggest that aestivation may have evolved several hundred million years ago.


Physiology

Organisms that aestivate appear to be in a fairly "light" state of dormancy, as their physiological state can be rapidly reversed, and the organism can quickly return to a normal state. A study done on '' Otala lactea'', a snail native to parts of Europe and Northern Africa, shows that they can wake from their dormant state within ten minutes of being introduced to a wetter environment. The primary physiological and biochemical concerns for an aestivating animal are to conserve energy, retain water in the body, ration the use of stored energy, handle the nitrogenous end products, and stabilize bodily organs, cells, and
macromolecule A macromolecule is a very large molecule important to biophysical processes, such as a protein or nucleic acid. It is composed of thousands of covalently bonded atoms. Many macromolecules are polymers of smaller molecules called monomers. ...
s. This can be quite a task as hot temperatures and arid conditions may last for months, in some cases for years. The depression of metabolic rate during aestivation causes a reduction in macromolecule synthesis and degradation. To stabilize the macromolecules, aestivators will enhance antioxidant defenses and elevate
chaperone proteins In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to assi ...
. This is a widely used strategy across all forms of hypometabolism. These physiological and biochemical concerns appear to be the core elements of hypometabolism throughout the animal kingdom. In other words, animals which aestivate appear to go through nearly the same physiological processes as animals that hibernate.


Invertebrates


Mollusca

Gastropoda: some air-breathing land snails, including species in the genera ''
Helix A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined hel ...
, Cernuella, Theba, Helicella, Achatina'' and ''
Otala ''Otala'' is a genus of land snails in the subfamily Helicinae of the family Helicidae. MolluscaBase eds. (2021). MolluscaBase. Otala Schumacher, 1817. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php ...
'', commonly aestivate during periods of heat. Some species move into shaded vegetation or rubble. Others climb up tall plants, including crop species as well as bushes and trees, and will also climb man-made structures such as posts, fences, etc. Their habit of climbing vegetation to aestivate has caused more than one introduced snail species to be declared an agricultural nuisance. To seal the opening to their shell to prevent water loss, pulmonate land snails secrete a membrane of dried mucus called an epiphragm. In certain species, such as ''
Helix pomatia ''Helix pomatia'', common names the Roman snail, Burgundy snail, or escargot, is a species of large, edible, air-breathing land snail, a pulmonate gastropod terrestrial mollusc in the family Helicidae.MolluscaBase eds. (2021). MolluscaBase. Helix ...
'', this barrier is reinforced with calcium carbonate, and thus it superficially resembles an operculum, except that it has a tiny hole to allow some oxygen exchange. There is a decrease in
metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cel ...
and reduced rate of water loss in aestivating snails like '' Rhagada tescorum'', '' Sphincterochila boissieri'' and others.


Arthropoda

Insecta Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
: Lady beetles (''
Coccinellidae Coccinellidae () is a widespread family of small beetles ranging in size from . They are commonly known as ladybugs in North America and ladybirds in Great Britain. Some entomologists prefer the names ladybird beetles or lady beetles as the ...
'') have been reported to aestivate. Mosquitoes also are reported to undergo aestivation. False honey ants are well known for being winter active and aestivate in temperate climates.
Bogong moth The bogong moth (''Agrotis infusa'') is a temperate species of night-flying moth, notable for its biannual long-distance seasonal migrations towards and from the Australian Alps, similar to the diurnal monarch butterfly. During the autumn a ...
s will aestivate over the summer to avoid the heat and lack of food sources. Adult alfalfa weevils ('' Hypera postica'') aestivate during the summer in the southeastern United States, during which their metabolism, respiration, and nervous systems show a dampening of activity.
Crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
: An example of a crustacean undergoing aestivation is with the Australian crab ''Austrothelphusa transversa ,'' which undergoes aestivation underground during the dry season''.''


Vertebrates


Reptiles and amphibians

Non-mammalian animals that aestivate include North American desert tortoises,
crocodile Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant ...
s, and
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
s. Some amphibians (e.g. the cane toad and greater siren) aestivate during the hot dry season by moving underground where it is cooler and more humid. The California red-legged frog may aestivate to conserve energy when its food and water supply is low. The
water-holding frog ''Ranoidea'' is a genus of frogs in the subfamily Pelodryadinae. They are found in Australia, New Guinea, and two nearby groups of islands: the Maluku Islands, and the Louisiade Archipelago. The circumscription of this taxon is still controve ...
has an aestivation cycle. It buries itself in sandy ground in a secreted, water-tight mucus cocoon during periods of hot, dry weather. Australian Aboriginals discovered a means to take advantage of this by digging up one of these frogs and squeezing it, causing the frog to empty its bladder. This dilute urine—up to half a glassful—can be drunk. However, this will cause the death of the frog which will be unable to survive until the next rainy season without the water it had stored. The western swamp turtle aestivates to survive hot summers in the ephemeral swamps it lives in. It buries itself in various media which change depending on location and available substrates. Because the species is critically endangered, the Perth Zoo began a conservation and breeding program for it. However, zookeepers were unaware of the importance of their aestivation cycle and during the first summer period would perform weekly checks on the animals. This repeated disturbance was detrimental to the health of the animals, with many losing significant weight and some dying. The zookeepers quickly changed their procedures and now leave their captive turtles undisturbed during their aestivation period.


Fish

African lungfish also aestivate as can
salamanderfish ''Lepidogalaxias salamandroides'' is a species of small fish of Western Australia. It is the monotypic, only member of the family Lepidogalaxiidae and genus ''Lepidogalaxias''. Common names for this fish include salamanderfish and Shannon mudminn ...
.


Mammals

Although relatively uncommon, a small number of mammals aestivate. Animal physiologist Kathrin Dausmann of Philipps University of Marburg,
Germany Germany, officially the Federal Republic of Germany (FRG),, is a country in Central Europe. It is the most populous member state of the European Union. Germany lies between the Baltic and North Sea to the north and the Alps to the sou ...
, and coworkers presented evidence in a 2004 edition of ''
Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...
'' that the Malagasy fat-tailed dwarf lemur hibernates or aestivates in a small tree hole for seven months of the year. According to the Oakland Zoo in California, four-toed hedgehogs are thought to aestivate during the dry season.


See also

* Critical thermal maximum *
Hibernation induction trigger 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 ...
*
Torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the tim ...


References


Further reading

*


External links


Abstract of an Australian paper on aestivation in snails






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