Summer rest

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The summer of rest , as summer sleeping referred Aestivation or estivation, is a form of reduced activity as adaptation to hot or dry environmental conditions, for example in a heat wave or a dry season under arid climatic conditions. Their ecological benefit lies in the reduction in energy consumption. Physiologically, mammals are a form of torpor in which the metabolism is switched to the back burner and the body temperature drops to ambient temperature. Cold weather animals often show a heat or dry rigidity.

Summer rest is a form of dormancy and is therefore sometimes also called summer dormancy . It can either be triggered directly by unfavorable environmental conditions (then called quiescence ) or, in the case of unfavorable conditions that occur regularly over the course of the year, by an external timer such as the length of the day, in which case it is a diapause .

Some authors differentiate between real summer dormancy (a torpor state lasting many days) from shorter torpor episodes that often occur daily and usually only last a few hours (sometimes called daytime sleep thargy).

physiology

Physiologically, summer dormancy does not differ from other forms of torpor. In contrast to hibernation , the ambient temperatures are usually higher, which means that the body temperature does not drop as much. As a result, the energy savings are lower due to the higher resting metabolism. By avoiding z. Some of the very energy-intensive functions of thermoregulation and regulation of body moisture, however, the energy saving compared to the active state is still substantial. Many animal species with dry sleep excrete substances that build up a protective body shell, for example snails close their houses with an epiphragm . Aesthetic frog species also take up large amounts of water beforehand in order to be able to better compensate for water losses in the resting state. Special adjustments are also required with regard to the nitrogen metabolism. Lungfish and other aesthetic species often store urea , as excretion would result in water loss . The enzyme AMP-activated protein kinase can play a key role in regulating the metabolism .

Waking up from the torpor state can, with suitable environmental stimuli, take place very quickly, within minutes. The torpor state has nothing to do with normal sleep. Except for the cellular level, most metabolic functions are either switched off or at least reduced to a minimum necessary for life support. A number of special adaptation mechanisms of hibernation, such as the burning of brown body fat to wake up, are never pronounced in the estivation. An adaptation to a reduced oxygen content ( hypoxia ), which is much better tolerated in the Torpor state, is typical .

Occur

Aesthetic occurs in mammals mainly in people living in arid regions, for example ground squirrels (Xerinae) and gerbils (Gerbillinae).

Summer dormancy of reptiles

During the summer dormancy, some species of reptile burrow in the ground. Some ( turtles , snakes , lizards ) sometimes use abandoned rodent burrows as shelter. Some (lizards, snakes) hide in protective crevices in the rock. During this time the animals do not consume any food.

The summer rest is the only possibility for these animals to survive the summer heat wave unscathed. In their rain-poor habitat ( macchia , semi-desert or desert ), these cold-blooded vertebrates would not be able to survive in midsummer without the summer rest phase due to the risk of overheating and a lack of food and water.

It is interesting that despite very high ambient temperatures of over 30 ° C to sometimes over 40 ° C air temperature, the animals' metabolism is so reduced that they do not lose weight during the entire summer rest period. How this is possible from a physiological point of view is not yet clear.

Presumably, the initiation of summer rest is controlled hormonally. The triggering factors are the absence of rain, strong sunlight, rising ambient temperatures (usually above 30 ° C) and the resulting increasing drying up of the forage plants (affects tortoises) or the disappearance of food insects (affects lizards) or other living beings used as food (affects snakes).

The duration of the summer rest depends on the weather conditions and can go from 2 weeks to 2 or even 3 months. Presumably the falling outside temperatures cause the resting animal to resume its activities. The exact physiological processes in the organism of summer resting reptiles have not yet been researched.

Examples of reptile species that hold summer dormancy:

See also

Web links

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Individual evidence

  1. Fritz Geiser: Aestivation in Mammals and Birds. In: Carlos Arturo Navas, José Eduardo Carvalho (Ed.): Aestivation. Molecular and Physiological Aspects. (= Progress in Molecular and Subcellular Biology. 49). Springer Verlag, 2010, pp. 95 to 111. doi: 10.1007 / 978-3-642-02421-4_5
  2. Kenneth B. Storey, Janet M. Storey: Aestivation: signaling and hypometabolism. In: Journal of Experimental Biology. 215, 2012, pp. 1425-1433. doi: 10.1242 / jeb.054403