Tonic Immobility and Thanatosis
Our Approach:
Tonic immobility is an involuntary animal behavior in which a catatonic state is induced. The animal remains conscious, but calm and immobile. In many species, this reaction is brought on by fear or extreme stress and may be considered a form of thanatosis.
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Thanatosis is the act of playing dead. It is an anti-predation behavior used by a plethora of animals, from opossums to spiders to chickens to snakes, and many others.
This website explores tonic immobility through the lens of Tinbergen's four questions. We will approach our behavior by looking at how it develops, its long-term evolution, the mechanism behind it, and its function. By using these guiding categories, we will have a more holistic understanding of tonic immobility. These four questions are four of many ways to look at a subject in animal behavior, but encompass the integrative nature of the subject, without compromising the depth of our research.
Figure 2. A table explaining the divide of Tinbergen's four questions, including the breakup of proximate and ultimate, and looks at a small, present scope versus a larger scope.
Thanatosis
Tonic Immobility
Figure 1. A Venn Diagram of Tonic Immobility as a subset of Thanatosis.
Animals That Exhibit Tonic Immobility
Sharks
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Tonic immobility in sharks is induced quite easily. Research shows it's as simple as flipping them on their backs. For humans, this creates a convenient alternative to sedation and has led to great strides in shark study. For sharks, having the ability to immobilize a a potential partner could be useful during mating.
Chickens
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Chickens are another species known to exhibit tonic immobility. Unlike sharks, it is likely that chickens enter the state in response to predators, either out of fear or intentionally.
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Snakes
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Snakes enter states of tonic immobility as well. At first thought, one might question why the snake, a predator, would have need for thanatosis (via tonic immobility). But it is important to remember that snakes too can be prey, and entering a state of tonic immobility could very well be life saving.