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Aestivation

life science Maturity 7-9 Next article →

Aestivation is a state of animal dormancy used to survive extreme conditions. It is very similar to hibernation, which occurs in the winter. However, aestivation takes place during the summer months. Animals enter this state in response to high temperatures and arid, or dry, conditions. This dormancy helps both terrestrial and aquatic animals avoid damage from heat. It also protects them from the risk of desiccation, which is when a body loses too much water.

Theba pisana on Foeniculum vulgare, Montbazin, Hérault 03
Theba pisana on Foeniculum vulgare, Montbazin, Hérault 03

To survive for months or even years, an animal must change how its body works. The primary goal is to conserve energy and retain water. Animals must also ration their stored energy and manage nitrogenous waste products. A key part of this is a lowered metabolic rate. This means the body's chemical processes slow down significantly. This reduction in metabolism causes a decrease in the synthesis and degradation of macromolecules. To keep these large molecules stable, aestivating animals increase their antioxidant defenses. They also elevate chaperone proteins to protect their cells and organs.

Kadina-snails-climb-fence-0716
Kadina-snails-climb-fence-0716

Invertebrates show many different ways of aestivating. Many land snails, such as those in the genera Helix, Cernuella, and Theba, use this strategy. These snails often move into shaded rubble or climb tall plants and human structures like fences. To prevent water loss, they secrete a dried mucus membrane called an epiphragm. In species like Helix pomatia, this barrier is reinforced with calcium carbonate. This makes the seal look like an operculum, but it has a tiny hole for oxygen exchange. Other invertebrates like lady beetles and Bogong moths also aestivate to avoid summer heat. In Australia, the crustacean Austrothelphusa transversa aestivates underground during the dry season.

Glanum-snail-climb-fence-5763
Glanum-snail-climb-fence-5763

Vertebrates also use aestivation to survive harsh environments. Some amphibians, such as the cane toad, move underground where it is cooler and more humid. The water-holding frog has a very specific aestivation cycle. It buries itself in sandy ground and creates a water-tight cocoon made of mucus. This cocoon helps the frog survive until the next rainy season. In the past, Australian Aboriginals discovered they could drink the dilute urine stored in these frogs. However, squeezing the frog to get the water would cause its death. Other vertebrates like North American desert tortoises, crocodiles, and salamanders also undergo this process.

Fossil records suggest that aestivation is an ancient biological strategy. It may have evolved several hundred million years ago. Scientists have proposed an interesting theory regarding two ancient creatures. A therapsid called Thrinaxodon liorhinus may have shared a burrow with an amphibian named Broomistega putterilli. Researchers believe they might have been aestivating together in the same space. This suggests that the need to escape heat through dormancy has existed for a very long time.

While less common, some mammals also participate in this behavior. In 2004, researchers presented evidence regarding the Malagasy fat-tailed dwarf lemur. They found that these lemurs may aestivate or hibernate in small tree holes for seven months of the year. Additionally, the four-toed hedgehog is thought to aestivate during the dry season. These examples show that even complex mammals can use dormancy to manage environmental stress. This behavior is a vital tool for survival in unpredictable climates.

The physiological processes of aestivation are closely linked to the concept of hypometabolism. This is a general term for the reduction of metabolic activity. The core elements of aestivation, such as stabilizing macromolecules and managing energy, are found throughout the animal kingdom. These processes are nearly identical to those used by animals that hibernate in the winter. Whether an animal is a snail, a fish like the African lungfish, or a mammal, the goal remains the same. They use these biological tools to wait out the heat until conditions become favorable again.

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Theba pisana on Foeniculum vulgare,...
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File:Glanum-snail-climb-fence-5763.jpg
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