Estivation or Aestivation – Definition and Examples


Estivation or Aestivation

Estivation, also spelled aestivation, is a state of dormancy or torpor that animals enter in response to extreme heat and arid conditions, primarily during the summer months. The term originates from the Latin word “aestivare,” which means “to spend the summer.” This adaptation helps animals conserve energy and reduce the need for water, which is often scarce in hot periods.

Spelling Variations

The spelling “estivation” is predominant American English, while “aestivation” is more common in British English. Both spellings are correct and refer to the same biological process.

The Role and Importance of Estivation

Estivation plays a crucial role in animal survival strategies. It helps animals avoid the harshest environmental conditions when resources are limited. By slowing down their metabolic rate, they reduce water and food needs, effectively bypassing periods when sustaining normal activities would be challenging or impossible. By effectively removing animals from the ecosystem, estivation also plays a significant role in predator-prey relationships, seed dispersal, and other processes.

The Process of Estivation

During estivation, animals undergo physiological changes. Their metabolic rate drops significantly, and bodily functions like heart rate and breathing slow down. Some species retreat to burrows or other sheltered environments, often sealing themselves in to reduce water loss and maintain a cooler environment. Some species produce highly concentrated urine. The length of estivation varies and lasts anywhere from a few days to several months, depending on the species and environmental conditions. Most animals emerge from estivation relatively quickly when environmental conditions improve.

Examples of Animals That Undergo Estivation

  • Invertebrates:
    • Insects: Certain beetles, snails, moths, ants, and earthworms. Specific examples include the alfalfa weevil (Hypera postica), Anopheles mosquitoes, the ladybug (Coccinella septempunctata), and the desert locust (Schistocerca gregaria).
    • Crustaceans: Some crab species, such as the purple marsh crab (Sesarma reticulatum) and Australian crab (Austrothelphusa transversa).
    • Gastropods: Land snails and slugs, for example, in the genera Helix, Otala, Cemuella, and Theba.
    • Annelids: Earthworms
  • Vertebrates:
    • Reptiles: Crocodiles, certain tortoises, and some snake species. Specific examples include the gopher tortoise (Gopherus polyphemus) and North American rattlesnake (Crotalus atrox).
    • Amphibians: Frogs, toads, and salamanders. Examples include the African bullfrog (Pyxicephalus adspersus) and spadefoot toads (Pelobates)
    • Fish: Lungfish (e.g., African lungfish Protopterus annectens)
    • Mammals: Some species of hedgehogs, lemurs, mice, and bats.
    • Birds: Some sources cite the hummingbird as an example of a bird that undergoes estivation. However, most references consider the avian response to hot an dry conditions as a form of torpor separate from estivation.

Each species listed here has developed unique adaptations for estivation. For example:

  • The African bullfrog creates a mucus cocoon that preserves moisture around its body.
  • The African lungfish burrows into mud and secretes a mucus cocoon, allowing it to breathe air through a built-in snorkel-like structure.
  • The hedgehog’s metabolism decreases significantly, allowing it to survive long periods without food or water.
  • Land snails seal their shells with a mucus-derived membrane to prevent desiccation.

Comparison to Hibernation and Brumation

Estivation is comparable to hibernation and brumation, which are forms of dormancy in response to cold temperatures. While hibernation is a strategy used primarily by mammals to conserve energy during winter when food is scarce, brumation is a similar state in cold-blooded animals, such as reptiles and amphibians. The primary difference lies in the trigger for these states: estivation is a response to heat and drought, while hibernation and brumation are responses to cold.

Overlap Between Estivation, Hibernation, and Brumation

Some animals engage in more than one form of dormancy. For example, certain species of desert tortoises estivate during extremely hot summer months and brumate during colder winter periods. The dormouse (Glis glis) engages in hibernation, daily torpor, and estivation. This versatility allows them to survive in environments with extreme seasonal temperature fluctuations.

References

  • Charlwood, J.D.; Vij, R.; Billingsley, P.F. (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
  • Cunningham, R. K.; Tombes, A. S. (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
  • Delaney, R. G.; Lahiri, S.; Fishman, A. P. (1974). “Aestivation of the African lungfish Protopterus aethiopicus: cardiovascular and respiratory functions”. Journal of Experimental Biology. 61 (1): 111–128. doi:10.1242/jeb.61.1.111
  • Navas, Carlos Arturo; Carvalho, José Eduardo (2009). Aestivation: Molecular and Physiological Aspects. Springer. ISBN 978-3-642-02420-7.
  • 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
  • Wilz, M.; Heldmaier, G. (2000). “Comparison of hibernation, estivation and daily torpor in the edible dormouse, Glis glis“. J Comp Physiol B. 170(7):511-21. doi: 10.1007/s003600000129