Torpor

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As torpor (lat, paralysis, numbness'.) Refers to a physiological state of sleep , the smaller of some mammals and birds , so in warm-blooded animals , occurs with a lethargy is comparable in the metabolism - and energy conversion processes are reduced to a minimum and all body functions are kept on the back burner , as it were. The affected animals are completely inactive and remain in a state of physical rigidity. There are hardly any reactions to external stimuli in this state. The torpor serves the animals mainly to survive long periods of lack of food or water; they can thus survive for a few days to several weeks without ingesting food or fluids.

Functional process in the organism to adapt to cold or dryness

Scientifically, this condition is called torpidity or torpor , often also called hypothermia . In the German-speaking world, the terms starvation , daytime sleep thargy , starvation or cold sleep are also known for this . Ornithological terms it is spoken of a locking .

Physiologically, starvation is similar to hibernation , but mostly it is not cold and lack of light or hormonal changes that are the triggering factors, but lack of food and the associated weight loss. All life-sustaining processes are reduced to a minimum, the body temperature drops significantly, but never as sharply as in real winter sleepers. The trigger for the torpor and longer dry periods are possible, it comes to a longer dry or summer mortis . The affected animals regularly wake up from the torpor when the environmental conditions have improved.

The torpor usually only occurs for a few hours and is usually used as a response to the current food situation and energy consumption. Each individual decides, depending on the situation, whether it goes in Torpor or not. If you are underweight , there is no decrease in body functions, which is also useful, as considerable energy reserves are required for the waking up phase.

The torpor differs from hibernation in that it only occurs for a limited time and can be used at any time, i.e. at any time and without physiological preparation. Hibernation is an inevitable behavior that requires weeks of preparation (fat storage, hormonal changes, etc.). With the Torpor, the body temperature is not lowered to as low as it is during hibernation. Nevertheless, energy can be saved through this state. The advantage over hibernation is that the animals do not have to give up their territory , do not need to withdraw and wake up again faster.

In some animals there may even be daily torpor cycles. It has been observed in hummingbirds that they can spontaneously put themselves into a short-term sleep state at night. The torpor also occurs in bats and the common house mouse . To do this, the bat lowers its body temperature below normal when sleeping.

Daily torpor is also known from mouse lemurs , the smallest primates in the world. If there is not enough food available at night during the dry season, lemurs go to torpor around midnight and lower their body temperature. You can slowly be heated up again passively with the sun towards morning and wake up from the torpor around noon. You then only spent a few hours in the torpor, but this saves up to 40% of your energy, especially through passive heating.

The torpor in birds

Since birds do not hibernate, the ability to fall into torpid states is quite common in them, but this possibility is limited to smaller species as waking up is relatively energy consuming. For larger and heavier species, this would result in an unfavorable ratio between energy savings and energy consumption in the waking phase. In the bird families of the sailors (Apodidae), swallows (Hirundinidae) and the night swallows (Caprimulgidae) there are some representatives that use the state of starvation as an energy-saving measure.

When cold air ingresses into Central Europe in summer, such conditions can also be observed in common swifts , especially in young animals.

House martins never get into torpor, even at low outside temperatures (minus 5 ° C and below), as long as they are well nourished. However, if your body weight sinks to around 15 grams (normal weight 19-20 grams), torpor occurs even at high night outside temperatures. The intensity of torpidity and thus the lowering of the body temperature at night depends on the nutritional status.

Some night swallows, such as the winter night swallow ( Phalaenoptilus nuttallii ) widespread in southwestern North America, overwinter in a state of deep torpidity. The Hopi -Indianer call him Hoelchko what with The Sleeping can be translated. Animals that are in such a state can no longer control the awakening themselves - only very clearly rising ambient temperatures initiate the awakening phase. A less deep torpidity, on the other hand, can be stopped by the bird itself, even if the outside temperature remains the same.

Even hummingbirds that live in night frost exposed regions, falling regularly in torpor, as these birds with their very high metabolic rate would otherwise not survive the long, cold nights. Your body temperature drops from the normal 38 - 40 ° C to 18 - 20 ° C, while the metabolic rate is reduced by up to 90% for just a few hours. With them this condition is more endogenously determined.

See also

Web links

  • Lennart Pyritz : Ancient & unfathomable. The hibernation phenomenon is more puzzling than expected . Air date: April 11, 2017, duration: 5:49 MP3

literature

  • Franz Bairlein : Ecology of the birds . Gustav Fischer, Stuttgart 1996, ISBN 3-437-25018-3 , pp. 9 and 10.
  • J. Schmid, JR Speakman: Daily energy expenditure of the gray mouse lemur (Microcebus murinus): a small primate that uses torpor. In: J. Comp. Physiol. Volume 170, 2000, pp. 633-641.
  • Josef H. Reichholf : The future of the species. 2nd Edition. 2011, ISBN 978-3-423-34532-3 , p. 50, chap. Common swift and water quality.
  • Lisa Warnecke: The Secret of Winter Sleepers - Travel to a Hidden World. Verlag CH Beck, Munich 2017, ISBN 978-3-406-71328-6 .