Estivation

Estivation or aestivation (from Latin "aestas", summer), also known as "summer sleep", is a state of dormancy somewhat similar to hibernation. It takes place during times of heat and dryness, the hot dry season, which is often but not inevitably the summer months.

Invertebrate and vertebrate animals are known to enter this state, in order to avoid damage from high temperatures and the risk of dehydration. Both terrestrial and aquatic animals undergo estivation.

Invertebrates

Mollusks

Certain air-breathing land snails, including species in the genera Helix, Cernuella, Helicella and Otala, commonly estivate during periods of heat. Some species move into shaded vegetation or rubble. Others climb up tall plants, including bushes and trees, and will also climb man-made structures such as posts, fences, etc, in order to get away from the intense ground heat.

The habit of climbing up vegetation in order to estivate has caused more than one introduced snail species to be declared a agricultural nuisance: a crop pest.

To seal the opening to their shell in order to prevent water loss, pulmonate land snails secrete a membrane called an epiphragm, which is made of dried mucus. 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.

Arthropods

Many land crabs spend dry seasons in an inactive state at the bottom of their burrows.

Vertebrates

Vertebrates which estivate include North American desert tortoises, crocodiles, salamanders, and lungfishes. The lungfish ("Protopterus") estivates by burying itself in mud formed at the surface of a dried up lake. First it forms a cocoon of dried mucus. It then forms a tube through which reduced respiration continues.

Some amphibians estivate during the hot dry season by moving underground where it is cooler and more humid. The California red-legged frog may estivate to conserve energy when its food and water supply is low.

Mammals

Until recently no primate, and no tropical mammal, was known to estivate. However, animal physiologist Kathrin Dausmann of Philipps University of Marburg, Germany, and coworkers presented evidence in the 24 June 2004 edition of "Nature" that the Madagascan fat-tailed dwarf lemur hibernates or estivates in a small cricket hollow for seven months of the year.

See also

* Torpor - regulated hypothermia for less than a day, often used by birds
* Hibernation induction trigger

References

* David Randall "et al", 2002, "Eckert Animal Physiology: Mechanisms and Adaptations", 5th Edition, W.H. Freeman and CO., New York, ISBN-13: 9780716738633

External links

* [http://www.publish.csiro.au/paper/ZO9680857.htm Abstract of an Australian paper on aestivation in snails]
* [http://www.publish.csiro.au/paper/ZO9680857.htm Some info in aestivation in the snail "Theba pisana"]
* [http://www.fhcrc.org/about/ne/news/2005/04/21/roth.html Hibernation on demand]
* [http://library.thinkquest.org/TQ0312800/estivation.htm Basic definition]