estivation

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Estivation or aestivation (from Latin aestas, summer), also known as "summer sleep", is a state of animal 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 to avoid damage from high temperatures and the risk of desiccation. Both terrestrial and aquatic animals undergo estivation.

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.

Lady beetles (Coccinellidae) have been reported to estivate.^[1]

Molluscs

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., to get away from the intense ground heat.

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

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 decrease in metabolic rate and reducing rate of water loss in aestivating snails like Rhagada tescorum^[2], Sphincterochila boissieri and others.

Arthropods

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

Vertebrates

Non-mammals that 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 (e.g. the cane toad and greater siren) 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.

Australian Aborigines discovered a means to take advantage of the estivation cycle of the Water-holding Frog, which buries itself in sandy ground in a secreted, water-tight, mucus cocoon during periods of hot, dry weather. Thirsty Aborigines may dig up the frog and gently squeeze it, causing the frog to release some of the fresh water it stores for itself in its bladder and skin pockets. This water may be drunk by the aborigine, who then releases the frog.

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 Malagasy fat-tailed dwarf lemur hibernates or estivates in a small cricket hollow for seven months of the year.

See also

• Critical thermal maximum
• Hibernation induction trigger
• Torpor

References

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

1. ^ Hagen, K.S. (1962) Biology and Ecology of Predaceous Coccinellidae. Annual Review of Entomology Vol. 7: 289-326
2. ^ Philip Withers, Scott Pedler & Michael Guppy. 1997. Physiological Adjustments during Aestivation by the Australian Land Snail Rhagada tescorum (Mollusca: Pulmonata: Camaenidae). Australian Journal of Zoology 45(6) 599 - 611. abstract.

External links

• Abstract of an Australian paper on aestivation in snails
• Some info in aestivation in the snail Theba pisana
• Hibernation on demand
• Basic definition

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