Aestivation

Aestivation (Latin: aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a lowered metabolic rate, that is entered in response to high temperatures and arid conditions.[1] It takes place during times of heat and dryness, the hot dry season, which are often the summer months.

This article is about a state of animal dormancy, similar to hibernation. For other uses, see Aestivation (disambiguation).

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Animal dormancy
Theba pisana snails aestivating on Foeniculum vulgare in Montbazin, France

Invertebrate and vertebrate animals are known to enter this state to avoid damage from high temperatures and the risk of desiccation. Both terrestrial and aquatic animals undergo aestivation. The fossil record suggests 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 macromolecules. This can be quite a task as hot temperatures and arid conditions may last for months. 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. 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.[2]

Invertebrates
Introduced Theba pisana snails aestivating on a row of fence posts in Kadina, South Australia
Numerous individuals of the snail Cernuella virgata aestivating on a wire fence near Glanum, in the south of France.

Mollusca

Gastropoda: some air-breathing land snails, including species in the genera Helix, Cernuella, Theba, Helicella, Achatina and Otala, 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, 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 and reduced rate of water loss in aestivating snails like Rhagada tescorum,[3] Sphincterochila boissieri and others.

Arthropoda

Insecta: Lady beetles (Coccinellidae) have been reported to aestivate.[4] Mosquitoes also are reported to undergo aestivation.[5] False honey ants are well known for being winter active and aestivate in temperate climates. Bogong moths will aestivate over the summer to avoid the heat and lack of food sources.[6] 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.[7][8]

Crustacea: An example of a crustacean undergoing aestivation is with the Australian crab Austrothelphusa transversa , which undergoes aestivation underground during the dry season.[9]

Vertebrates

Reptiles and amphibians

Non-mammalian animals that aestivate include North American desert tortoises, crocodiles, and salamanders. 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.[11]

The water-holding frog has an aestivation cycle. It buries itself in sandy ground in a secreted, water-tight mucus cocoon during periods of hot, dry weather. Australian Aborigines 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.[12]

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.[13] 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[14][15] as can salamanderfish.

Mammals

Although relatively uncommon, a small number of mammals aestivate.[16] Animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in a 2004 edition of Nature that the Malagasy fat-tailed dwarf lemur hibernates or aestivates in a small tree hole for seven months of the year.[17] According to the Oakland Zoo in California, East African hedgehogs are thought to aestivate during the dry season.[18]

See also

References
  1. Miller, William Charles (2007). Trace Fossils: Concepts, Problems, Prospects. Elsevier. p. 206. ISBN 978-0-444-52949-7.
  2. Storey, Kenneth B.; Storey, Janet M. (2012). "Aestivation: signaling and hypometabolism". The Journal of Experimental Biology. 215 (8): 1425–1433. doi:10.1242/jeb.054403. PMID 22496277.
  3. Withers, Philip; Pedler, Scott; Guppy, Michael (1997). "Physiological adjustments during aestivation by the Australian land snail Rhagada tescorum (Mollusca: Pulmonata: Camaenidae)". Australian Journal of Zoology. 45 (6): 599–611. doi:10.1071/ZO97009.
  4. Hagen, Kenneth S. (1962). "Biology and ecology of predaceous Coccinellidae". Annual Review of Entomology. 7: 289–326. doi:10.1146/annurev.en.07.010162.001445.
  5. Charlwood, JD; Vij, R; Billingsley, PF (2000). "Dry season refugia of malaria-transmitting mosquitoes in a dry savannah zone of east Africa". American Journal of Tropical Medicine and Hygiene. 62 (6): 726–732. doi:10.4269/ajtmh.2000.62.726. PMID 11304064.
  6. Common, I. F. B. (1954). "A study of the ecology of the adult bogong moth, Agrotis infusa (Boisd) (Lepidoptera: Noctuidae), with special reference to its behaviour during migration and aestivation". Australian Journal of Zoology. 2 (2): 223–263. doi:10.1071/zo9540223.
  7. Cunningham, R. K.; Tombes, A. S. (August 1966). "Succinate oxidase system in the alfalfa weevil, Hypera postica, during aestivation (summer diapause)". Comparative Biochemistry and Physiology. 18 (4): 725–733. doi:10.1016/0010-406x(66)90207-6. ISSN 0010-406X. PMID 5967408.
  8. Kutyna, F. A.; Tombes, A. S. (26 November 1966). "Bioelectric activity of the central nervous system in normal and diapausing alfalfa weevils". Nature. 212 (5065): 956–957. Bibcode:1966Natur.212..956K. doi:10.1038/212956a0. ISSN 0028-0836. PMID 6003744. S2CID 4205279.
  9. Waltham, Nathan J. (2016). "Unravelling life history of the Inland Freshwater Crab Austrothelphusa transversa in seasonal tropical river catchments". Australian Zoologist. 38 (2): 217–222. doi:10.7882/az.2016.034.
  10. Fernandez, V.; Abdala, F.; Carlson, K. J.; Cook, D. C.; Rubidge, B. S.; Yates, A.; Tafforeau, P. (2013). Butler, Richard J (ed.). "Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow". PLOS ONE. 8 (6): e64978. Bibcode:2013PLoSO...864978F. doi:10.1371/journal.pone.0064978. PMC 3689844. PMID 23805181.
  11. Moore, Bob (29 September 2009). "Estivation: The Survival Siesta". Audubon Guides. Retrieved 5 September 2012.
  12. Pough, F. H.; Andrews, R. M.; Cadle, J. E.; Crump, M. L.; Savitzky, A. H.; Wells, K. D. (2001). Herpetology, second edition. Upper Saddle River, New Jersey: Prentice Hall.
  13. Burbrige, Andrew; Kuchling, Gerald (2004). Western swamp tortoise (Pseudemydura umbrina) recovery plan (PDF) (3 ed.). Perth, Western Australia: Dept. of Conservation and Land Management. Retrieved 26 November 2015.
  14. Delaney, R. G.; Lahiri, S.; Fishman, A. P. (1974). "Aestivation of the African lungfish Protopterus aethiopicus: cardiovascular and respiratory functions" (PDF). Journal of Experimental Biology. 61 (1): 111–128. PMID 4411892.
  15. Fishman, A. P.; Galante, R. J.; Winokur, A.; Pack, A. I. (1992). "Estivation in the African lungfish". Proc. Am. Philos. Soc. 136 (1): 61–72. JSTOR 986798.
  16. McNab, Brian Keith (2002). The physiological ecology of vertebrates: a view from energetics. Cornell University Press. p. 388. ISBN 978-0-8014-3913-1.
  17. Dausmann, Kathrin H.; Glos, Julian; Ganzhorn, Jörg U.; Heldmaier, Gerhard (2004). "Physiology: hibernation in a tropical primate". Nature. 429 (6994): 825–826. Bibcode:2004Natur.429..825D. doi:10.1038/429825a. PMID 15215852. S2CID 4366123.
  18. "East African Hedgehog". Oakland Zoo. Archived from the original on 7 August 2016. Retrieved 5 September 2012.

Further reading
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