Apparent death
This article is about the behavior of animals. For the disease, see cataplexy. For the Australian hockey player, see Kate Starre.
Rigor mortis is a state of complete immobility. It occurs when an animal is threatened by a predator or is placed in a sudden stressful situation for other reasons. Alternative names are rigidity, stasis reflex, thanatosis, catalepsy and akinesia.
This behavior is found, for example, in insects, spiders and birds, and also in reptiles that are threatened by snakes. In birds it is caused, among other things, by a forced supine position. Many stick insects let themselves fall with their legs folded in order to be undetectable for predators due to their resemblance to plant parts. In laboratory rats, rigor mortis is used to infer the efficacy of various drugs in reducing pain and fear or to infer mechanisms of fear and fear processing.
Rigidity of fright is biologically expedient in that some predators react primarily to the movement of the prey animal (for example, snakes). Rats only flee if in a given situation an escape possibility can also be recognized; otherwise, in addition to rigor mortis, there is also a release of endogenous opioids - regardless of whether the triggering stimulus is a cat (as an innate enemy image) or an electric shock.
The possible adaptive value of rigor mortis was also experimentally demonstrated in a beetle species (red-brown flour beetle) against a jumping spider species as a predator. The jumping spiders preyed less on flour beetles from experimentally produced breeding lines that maintained a longer rigidity than from those that released it earlier.
In the Myotonic Goats, an American breed of goat, their unusual startle response is caused by a hereditary disease (myotonia).
Fright stare at a grasped swift fledgling
See also
- Rigor mortis
- Chicken Hypnosis
- Supporting starch
- Panic Disorder
Questions and Answers
Q: What is tonic immobility?
A: Tonic immobility is a natural state of paralysis that animals enter, often called animal hypnosis.
Q: What is the function of tonic immobility?
A: The function of tonic immobility is not certain, but it may be related to mating in certain animals like sharks and mammalia. It may also be a way of avoiding or deterring predators (playing dead is called thanatosis). Tonic immobility plays a role in survival if it helps a hunted animal to blend in with its surroundings.
Q: How can tonic immobility be induced in animals?
A: Tonic immobility can be induced without causing any apparent stress to the animal. For example, stroking a particular area of a lobster's shell or focusing a hen's attention on a line on the ground.
Q: What is thanatosis?
A: Thanatosis is the state of playing dead that animals adopt to avoid or deter predators.
Q: Is tonic immobility exclusive to animals?
A: No, tonic immobility has also been said to occur in humans that are subject to intense trauma, such as rape or sexual assault.
Q: What is catatonia?
A: Catatonia is a serious psychiatric condition that often involves a state of immobility.
Q: Can tonic immobility cause stress to animals?
A: Tonic immobility can be induced without causing any apparent stress to the animal.
