Apparent death#Thanatosis

{{Short description|Behavior in which animals take on the appearance of being dead}}

File:Opossum2.jpg (Didelphis virginiana) playing dead]]

File:Grass_Snake_(Natrix_natrix_helvetica)_playing_dead_(14178349634).jpg (Natrix helvetica) playing dead]]

Apparent death{{efn|Alternative names include playing dead, feigning death, playing possum, thanatosis, animal hypnosis, immobilization catatonia, or tonic immobility, the latter of which is preferred in the scientific literature on the subject.{{Cite journal|last1=Rogers|first1=Stephen M.|last2=Simpson|first2=Stephen J.|date=2014|title=Thanatosis|journal=Current Biology|language=en|volume=24|issue=21|pages=R1031–3|doi=10.1016/j.cub.2014.08.051|pmid=25517363|s2cid=235311966|doi-access=free|bibcode=2014CBio...24R1031R }}{{Cite journal|last1=Rusinova|first1=E. V.|last2=Davydov|first2=V. I.|date=2010-05-21|title=Dynamics of Changes in Electrical Activity in the Rabbit Cerebral Cortex during Sequential Sessions of "Animal Hypnosis"|journal=Neuroscience and Behavioral Physiology|volume=40|issue=5|pages=471–8|doi=10.1007/s11055-010-9283-7|pmid=20490695|s2cid=20118773|issn=0097-0549}}}} is a behavior in which animals take on the appearance of being dead. It is an immobile state most often triggered by a predatory attack and can be found in a wide range of animals from insects and crustaceans to mammals, birds, reptiles, amphibians, and fish.{{Cite journal|last1=Humphreys|first1=Rosalind K.|last2=Ruxton|first2=Graeme D.|date=2018-01-15|title=A review of thanatosis (death feigning) as an anti-predator behaviour|journal=Behavioral Ecology and Sociobiology |volume=72|issue=2|pages=22|doi=10.1007/s00265-017-2436-8 |pmc=5769822|pmid=29386702|bibcode=2018BEcoS..72...22H }}{{Cite journal|last1=Miyatake|first1=T.|last2=Katayama|first2=K.|last3=Takeda|first3=Y.|last4=Nakashima|first4=A.|last5=Sugita|first5=A.|last6=Mizumoto|first6=M.|date=2004-11-07|title=Is death–feigning adaptive? Heritable variation in fitness difference of death–feigning behaviour|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|language=en|volume=271|issue=1554|pages=2293–96|doi=10.1098/rspb.2004.2858|issn=0962-8452|pmc=1691851|pmid=15539355}}{{Cite book|url=http://link.springer.com/10.1007/978-981-33-6598-8|title=Death-Feigning in Insects: Mechanism and Function of Tonic Immobility|date=2021|publisher=Springer Singapore|isbn=978-981-336-597-1|editor-last=Sakai|editor-first=Masaki|series=Entomology Monographs|location=Singapore|language=en|doi=10.1007/978-981-33-6598-8|s2cid=232415330}} Apparent death is separate from the freezing behavior seen in some animals.

Apparent death is a form of animal deception considered to be an anti-predator strategy, but it can also be used as a form of aggressive mimicry. When induced by humans, the state is sometimes colloquially known as animal hypnosis. The earliest written record of "animal hypnosis" dates back to the year 1646 in a report by Athanasius Kircher, in which he subdued chickens.{{cite journal|last1=Gilman|first1=T.T.|last2=Marcuse|first2=F.L.|last3=Moore|first3=A.U.|year=1960|title=Animal hypnosis: a study of the induction of tonic immobility in chickens|journal=Journal of Comparative Physiology and Psychology|volume=43|issue=2|pages=99–111|doi=10.1037/h0053659|pmid=15415476}}

Description

{{multiple image

| align = right

| direction = vertical

| width = 250

| image1 = PhyllomedusaBurmeisteri (6).JPG

| alt1 =

| caption1 = {{center|Burmeister's leaf frog playing dead}}

| image2 = ApusApusKlausRoggel02.jpg

| alt2 =

| caption2 = {{center|Young common swift}}

| image3 = Iridomyrmex purpureus attacking Rhytidoponera metallica.jpg

| alt3 =

| caption3 = Black house ants attacking a green-head ant which has gone into tonic immobility

}}{{Anchor|Tonic immobility}}

Tonic immobility (also known as the act of feigning death, or exhibiting thanatosis) is a behaviour in which some animals become apparently temporarily paralysed and unresponsive to external stimuli. Tonic immobility is most generally considered to be an anti-predator behavior because it occurs most often in response to an extreme threat such as being captured by a (perceived) predator. Some animals use it to attract prey or facilitate reproduction. For example, in sharks exhibiting the behaviour, some scientists relate it to mating, arguing that biting by the male immobilizes the female and thus facilitates mating.{{cite journal | last1 = Henningsen | first1 = A.D. | year = 1994 | title = Tonic immobility in 12 elasmobranchs — use as an aid in captive husbandry | journal = Zoo Biology | volume = 13 | issue = 4| pages = 325–332 | doi = 10.1002/zoo.1430130406 }}

Despite appearances, some animals remain conscious throughout tonic immobility.{{cite journal|author=Jones, R.B|title=The tonic immobility reaction of the domestic fowl: a review|journal=World's Poultry Science Journal|volume=42|issue=1|year=1986|pages=82–96|doi=10.1079/WPS19860008}} Evidence for this includes the occasional responsive movement, scanning of the environment and animals in tonic immobility often taking advantage of escape opportunities. Tonic immobility is preferred in the literature because it has neutral connotations compared to 'thanatosis' which has a strong association with death.

Difference from freezing

Tonic immobility is different from freezing behavior in animals. A deer in headlights and an opossum "playing dead" are common examples of an animal freezing and tonic immobility, respectively. Freezing occurs early during a predator-prey interaction when the prey detects and identifies the threat, but the predator has not yet seen the prey. Because freezing occurs before detection and is used to better camouflage the prey and prevent the predator from attacking, it is considered a primary defense mechanism.

Tonic immobility occurs after the predator has detected and or made contact with the prey, and is likely used to prevent further attack by the predator or consumption of the prey. Because tonic immobility occurs later in the predator attack sequence, it is considered a secondary defense mechanism and is therefore distinct from freezing. Although freezing animals become rigid, they often stay upright and do not change their posture while frozen whereas during tonic immobility, animals often become rigid and change their posture.

Freezing behavior and tonic immobility are similar in that both may induce bradycardia (slowing of the heart rate), but the freezing response may instead be accompanied by rapid or increased breathing rate, increased heart rate, increased blood pressure and inhibition of digestion, depending on whether the sympathetic or parasympathetic nervous system is engaged.{{Cite journal |last=Roelofs |first=Karin |author-link=Karin Roelofs |date=2017-02-27 |title=Freeze for action: neurobiological mechanisms in animal and human freezing |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |volume=372 |issue=1718 |pages=20160206 |doi=10.1098/rstb.2016.0206 |pmc=5332864 |pmid=28242739}} In contrast, along with bradycardia, vertebrates in tonic immobility often reduce their breathing rate or protrude their tongue, further distinguishing this behavior from the freezing response.

Defensive

For defensive purposes, thanatosis hinges on the pursuer's becoming unresponsive to its victim, as most predators only catch live prey.{{cite journal | last1 = Pasteur | first1 = G | year = 1982 | title = A classificatory review of mimicry systems | journal = Annual Review of Ecology and Systematics | volume = 13 | issue = 1 | pages = 169–199 | doi = 10.1146/annurev.es.13.110182.001125 | bibcode = 1982AnRES..13..169P }}

In beetles, artificial selection experiments have shown that there is heritable variation for length of death-feigning. Those selected for longer death-feigning durations are at a selective advantage to those at shorter durations when a predator is introduced,{{Cite journal|last1=Miyatake|first1 = T|last2 = Katayama|first2 = K.|last3 = Takeda|first3 = Y.|last4 = Nakashima|first4 = A.|last5 = Mizumoto|first5 = M.|year = 2004|title = Is death-feigning adaptive? Heritable variation in fitness difference of death-feigning behaviour|journal = Proceedings of the Royal Society B |volume = 271|pages = 2293–96|doi = 10.1098/rspb.2004.2858|pmid=15539355|last6=Mizumoto|first6=M|issue=1554|pmc=1691851}} which suggests that thanatosis is indeed adaptive.

In the hog-nosed snake, a threatened individual rolls onto its back and appears to be dead when threatened by a predator, while a foul-smelling, volatile fluid oozes from its body. Predators, such as cats, then lose interest in the snake, which both looks and smells dead. One reason for their loss of interest is that rotten-smelling animals are instinctively avoided as a precaution against infectious disease, so the snake's adaptions exploit that reaction. Newly hatched young also instinctively show this behaviour when rats try to eat them.Triumph of Life (2006). Alexandria, VA: PBS Home Video.

In mammals, the Virginia opossum (commonly known simply as possums) is perhaps the best known example of defensive thanatosis. "Playing possum" is an idiomatic phrase which means "pretending to be dead".{{cite book|title =The Chambers Dictionary|publisher =Allied Publishers|year =1998|page=1279|isbn =978-81-86062-25-8|url =https://books.google.com/books?id=pz2ORay2HWoC}} It comes from a characteristic of the Virginia opossum, which is famous for reacting with a death-like posture when threatened.{{cite journal|last = Francq|first = E.|year = 1969|title = Behavioural aspects of feigned death in the opossum Didelphis marsupialis|journal = American Midland Naturalist|volume = 81|pages = 556–568|doi = 10.2307/2423988|issue = 2|jstor = 2423988}}{{cite web|url=http://www.wonderfulwv.com/archives/july00/fea2.cfm |title=Playing Possum |publisher=Wonderful West Virginia |author=Ann Bailey Dunn |access-date=May 11, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20111001110406/http://www.wonderfulwv.com/archives/july00/fea2.cfm |archive-date=October 1, 2011 }} This instinct does not always pay off in the modern world; for example, opossums scavenging roadkill may react with the death-like posture to the threat posed by oncoming traffic, and subsequently end up as roadkill themselves.{{cite web|url=http://www.massaudubon.org/Nature_Connection/wildlife/index.php?subject=Mammals&id=71|title=Virginia Opossum|publisher=Mass Audubon|access-date=May 11, 2011|quote=Opossums are frequently encountered as corpses along highways. Some biologists believe that many die as they feed on road-killed animals — a favorite food. Others believe that the opossums' small brain (5 times smaller than that of a raccoon) suggests that they may just be too dumb to get out of the way of vehicles!|archive-url=https://web.archive.org/web/20101229120106/http://www.massaudubon.org/Nature_Connection/wildlife/index.php?subject=Mammals&id=71|archive-date=December 29, 2010|url-status=dead}} "Playing possum" can also mean simply pretending to be injured, unconscious, asleep, or otherwise vulnerable, often to lure an opponent into a vulnerable position.

The usual advice for humans attempting to survive an attack by a brown bear is to lie face down, cover the face with one's hands/arms/elbows, and 'play dead'.{{Cite web |title=How to survive a bear attack |url=http://www.mnn.com/earth-matters/animals/stories/how-to-survive-a-bear-attack}}

Thanatosis has also been observed in many invertebrates such as the wasp Nasonia vitripennis,{{cite journal|last = King|first = B.|author2=H. Leaich |year = 2006|title = Variation in propensity to exhibit thanatosis in Nasonia vitripennis (Hymenoptera: Pteromalidae)|journal = Journal of Insect Behavior|volume = 19|issue = 2|pages = 241–9|doi = 10.1007/s10905-006-9022-7| bibcode=2006JIBeh..19..241K |citeseerx = 10.1.1.581.3100|s2cid = 26623855}} and the cricket, Gryllus bimaculatus.{{cite journal|last = Nishino|first = H.|year = 2004|title = Motor output characterizing thanatosis in the cricket Gryllus bimaculatus|journal = Journal of Experimental Biology|volume =207|issue = 22|pages = 3899–3915|doi=10.1242/jeb.01220|pmid = 15472021|doi-access = free| bibcode=2004JExpB.207.3899N }}

Reproductive

In the spider species Pisaura mirabilis, male spiders often stage elaborate rituals of gift-giving and thanatosis to avoid getting eaten by female spiders during mating. Studies have shown higher chances of success in mating with females for males who exhibit death-feigning more frequently than for males who do it less.{{cite journal|author1=Line Spinner Hansen |author2=Sofia Fernandez Gonzales |author3=Søren Toft |author4=Trine Bilde |year=2008|title=Thanatosis as an adaptive male mating strategy in the nuptial gift–giving spider Pisaura mirabilis|journal=Behavioral Ecology|volume=19 |issue=3|pages=546–551|doi=10.1093/beheco/arm165|doi-access=free}}

Predatory

File:Adult male livingstonii.pngs of the genus Nimbochromis use thanatosis as a form of aggressive mimicry, playing dead to attract prey]]

Nimbochromis (sleeper cichlids), endemic to Lake Malawi in East Africa, are large predatory fish for whom thanatosis is a form of aggressive mimicry. This fish will lie down on its side on the bottom sediments and assume a blotchy coloration. Scavengers, attracted to what seems like a dead fish, will approach the predator to investigate. N. livingstoni then abandons the thanatosis, righting itself again and quickly eating any scavenger unfortunate enough to come too close.{{cite book|author1=Gene S. Helfman |author2=Bruce B. Collette |author3=Douglas E. Facey |title =The diversity of fishes|publisher =Wiley-Blackwell|year =1997|page=324|isbn =978-0-86542-256-8|url =https://books.google.com/books?id=pz2ORay2HWoC}}{{cite journal | last1 = McKaye | first1 = K.R. | year = 1981 | title = Field observation on death feigning: a unique hunting behavior by the predatory cichlid, Haplochromis livingstonii, of Lake Malawi | journal = Environmental Biology of Fishes | volume = 6 | issue = 3–4| pages = 361–5 | doi = 10.1007/bf00005766 | bibcode = 1981EnvBF...6..361M | s2cid = 24244576 }} A similar strategy has also been observed in the African cichlid Lamprologus lemairii from Lake Tanganyika{{cite journal | last1 = Lucanus | first1 = O | year = 1998 | title = Darwin's pond: Malawi and Tanganyika | journal = Tropical Fish Hobbyist | volume = 47 | pages = 150–4 }} and in the Central American yellowjacket cichlid Parachromis friedrichsthalii.{{cite journal | last1 = Tobler | first1 = M | year = 2005 | title = Feigning death in the Central American cichlid Parachromis friedrichsthalii | journal = Journal of Fish Biology | volume = 66 | issue = 3| pages = 877–881 | doi = 10.1111/j.0022-1112.2005.00648.x | bibcode = 2005JFBio..66..877T }}

Examples

= Invertebrates =

File:Latrodectus geometricus female in thanatosis.JPG resorting to thanatosis after being shaken from her web]]

Within the invertebrates, tonic immobility is widespread throughout phylum Arthropoda and has been demonstrated to occur in beetles, moths, mantids, cicadas, crickets, spiders, wasps, bees, and ants.{{Cite journal|last1=Amemiya|first1=Mio|last2=Sasakawa|first2=Kôji|date=2021-01-10|title=Factors Affecting Thanatosis in the Braconid Parasitoid Wasp Heterospilus prosopidis|journal=Insects|volume=12|issue=1|pages=48|doi=10.3390/insects12010048 |pmid=33435169| pmc=7826778|doi-access=free}}{{Cite journal|last1=Martinez|first1=Alexander|last2=Ritzi|first2=Christopher M.|date=2020-03-31|title=Duration of Thanatosis is Based on Temperature in Estigmene acrea1|journal=Southwestern Entomologist|volume=45|issue=1|pages=289|doi=10.3958/059.045.0130|s2cid=214718486|issn=0147-1724}}{{Cite journal|last1=Cassill|first1=Deby L.|last2=Vo|first2=Kim|last3=Becker|first3=Brandie|date=2008-04-05|title=Young fire ant workers feign death and survive aggressive neighbors|journal=Naturwissenschaften|volume=95|issue=7|pages=617–624|doi=10.1007/s00114-008-0362-3|pmid=18392601|bibcode=2008NW.....95..617C|s2cid=2942824|issn=0028-1042}}{{Cite journal|last1=King|first1=B. H.|last2=Leaich|first2=H. R.|date=2006|title=Variation in Propensity to Exhibit Thanatosis in Nasonia vitripennis (Hymenoptera: Pteromalidae)|journal=Journal of Insect Behavior|volume=19|issue=2|pages=241–9|doi=10.1007/s10905-006-9022-7|bibcode=2006JIBeh..19..241K |s2cid=26623855|issn=0892-7553}}

== Wasps ==

Tonic immobility has been observed in several species of parasitoid wasp and is considered to be an antipredator behavior in these insects. In wasps, tonic immobility can be induced by tapping their antennae, tapping the abdomen repeatedly, or squeezing their abdomen. A study in 2020 found that the frequency and duration of tonic immobility was affected by the sex of the wasp and the temperature of the environment, but not the color of the background the wasp was on. These results were consistent with a study in 2006 that found no effect of background color on tonic immobility in a different wasp species, Nasonia vitripennis.

== Fire ants ==

In fire ant colonies, tonic immobility is used by young workers to avoid conflict with competing ants. In the fire ant species Solenopsis invicta, the tendency to exhibit thanatosis decreases with age, with older ants choosing to fight with any workers from neighboring colonies. By using tonic immobility to evade conflict, the researchers found that the young ants were four times more likely to survive an attack compared to their older counterparts, despite being more vulnerable due to their softer exoskeletons.

== Spiders ==

In the nuptial gift-giving spider, thanatosis is incorporated into their mating display. A study in 2008 demonstrated that male Pisaura mirabilis spiders who displayed thanatosis were more likely to copulate with females and copulated longer.

== Green Lacewings ==

Larvae of Chrysoperla plorabunda engage in tonic immobility when they come into close proximity with a predator.{{Cite journal |last1=Taylor |first1=Katherine L. |last2=Henry |first2=Charles S. |last3=Farkas |first3=Timothy E. |date=21 July 2023 |title=Why fake death? Environmental and genetic control of tonic immobility in larval lacewings (Neuroptera: Chrysopidae) |url=https://academic.oup.com/jinsectscience/article/doi/10.1093/jisesa/iead066/7238710 |journal=Journal of Insect Science |volume=23 |issue=4 |doi=10.1093/jisesa/iead066 |pmc=10407979 |pmid=37551937}} Usage of tonic immobility as an antipredator strategy has been shown to vary with energy availability and within-population genetic variation, with lacewings under energetic stress being more likely to engage in tonic immobility.

= Vertebrates =

Tonic immobility has been observed in a large number of vertebrate taxa, including sharks, fish, amphibians, reptiles, birds, and mammals.

==Sharks==

Some sharks can be induced into tonic immobility by inverting them and restraining them by hand, e.g. dogfish sharks, lemon sharks, whitetip reef sharks.{{cite journal | last1 = Whitman | first1 = P.A. | last2 = Marshall | first2 = J.A. | last3 = Keller | first3 = E.C.Jr | year = 1986 | title = Tonic immobility in the smooth dogfish shark, Mustelus canis (Pisces, Carcharhinidae) | journal = Copeia | volume = 1986 | issue = 3| pages = 829–832 | doi = 10.2307/1444973 | jstor = 1444973 }}{{cite journal | last1 = Watsky | first1 = M.A. | last2 = Gruber | first2 = S.H. | year = 1990 | title = Induction and duration of tonic immobility in the lemon shark, Negaprion brevirostris | journal = Fish Physiology and Biochemistry | volume = 8 | issue = 3| pages = 207–210 | doi = 10.1007/bf00004459 | pmid = 24221983 | bibcode = 1990FPBio...8..207W | s2cid = 6763380 }}{{cite journal | last1 = Davie | first1 = P.S. | last2 = Franklin | first2 = C.E. | last3 = Grigg | first3 = G.C. | year = 1993 | title = Blood pressure and heart rate during tonic immobility in the black tipped reef shark, Carcharhinus melanoptera | journal = Fish Physiology and Biochemistry | volume = 12 | issue = 2| pages = 95–100 | doi = 10.1007/bf00004374 | pmid = 24202688 | bibcode = 1993FPBio..12...95D | s2cid = 19258658 }} For tiger sharks (measuring 3–4 metres in length), tonic immobility can be induced by humans placing their hands lightly on the sides of the animal's snout in the area surrounding the eyes. During tonic immobility in sharks, the dorsal fins straighten, and both breathing{{Disputed inline|Sharks breathing|date=May 2020}} and muscle contractions become more steady and relaxed. This state persists for an average of 15 minutes before recovery and the resumption of active behaviour. Scientists have exploited this response to study shark behaviour; chemical shark repellent has been studied to test its effectiveness and to more accurately estimate dose sizes, concentrations and time to recovery.{{cite web|title=Tonic immobility|website=Shark defense: Chemical repellents|url=http://www.sharkdefense.com/Repellents/Tonic_Immobility/tonic_immobility.html|access-date=January 28, 2006|archive-url=https://web.archive.org/web/20060614111606/http://www.sharkdefense.com/Repellents/Tonic_Immobility/tonic_immobility.html|archive-date=June 14, 2006|url-status=dead}} Tonic immobility can also be used as a form of mild anesthesia during experimental manipulations of sharks.{{cite journal | last1 = Heithaus | first1 = M.R. | last2 = Dill | first2 = L.M. | last3 = Marshall | first3 = G.J. | last4 = Buhleier | first4 = B. | year = 2002 | title = Habitat use and foraging behavior of tiger sharks (Galeocerdo cuvier) in a seagrass ecosystem | journal = Marine Biology | volume = 140 | issue = 2| pages = 237–248 | doi = 10.1007/s00227-001-0711-7 | bibcode = 2002MarBi.140..237M | s2cid = 83545503 }}{{cite journal | last1 = Holland | first1 = K.N. | last2 = Wetherbee | first2 = B.M. | last3 = Lowe | first3 = C.G. | last4 = Meyer | first4 = C.G. | year = 1999 | title = Movements of tiger sharks (Galeocerdo cuvier) in coastal Hawaiian waters | journal = Marine Biology | volume = 134 | issue = 4| pages = 665–673 | doi = 10.1007/s002270050582 | bibcode = 1999MarBi.134..665H | s2cid = 7687775 }}

Scientists also believe that tonic immobility can be a stressful experience for sharks. By measuring blood chemistry samples when the shark is immobile, it has been suggested that tonic immobility can actually put stress on the shark, and reduce breathing efficiency. Others think sharks have a series of compensatory mechanisms that work to increase respiration rates and lower stress.Brooks, E. J., et al. "The Stress Physiology of Extended Duration Tonic Immobility in the Juvenile Lemon Shark, Negaprion Brevirostris (Poey 1868)." Journal of experimental marine biology and ecology 409.1-2 (2011): 351-60.

It has been observed that orcas can exploit sharks' tonic immobility to prey on large sharks. Some orcas ram sharks from the side to stun them, then flip the sharks to induce tonic immobility and keep them in such state for sustained time. For some sharks, this prevents water from flowing through their gills and the result can be fatal.{{cite news|author1=Lauren Smith|title=Orcas vs great white sharks: in a battle of the apex predators who wins?|url=https://www.theguardian.com/science/blog/2017/nov/16/orca-whales-vs-great-white-sharks-in-a-battle-of-the-apex-predators-who-wins|newspaper=The Guardian|access-date=2017-11-18|date=2017-11-16}}

==Teleost fishes==

Goldfish, trout, rudd, tench, brown bullhead, medaka, paradise fish, and topminnow have been reported to go limp when they are restrained on their backs.{{cite journal | last1 = Table | last2 = Whitman | first2 = P.A. | last3 = Marshall | first3 = J.A. | last4 = Keller | first4 = E.C.Jr | year = 1986 | title = Tonic immobility in the smooth dogfish shark, Mustelus canis (Pisces, Carcharhinidae) | journal = Copeia | volume = 1986 | issue = 3| pages = 829–832 | doi = 10.2307/1444973| jstor = 1444973}} Oscars seem to go into shock when they are stressed (when their aquarium is being cleaned, for example): they lie on their side, stop moving their fins, start to breathe more slowly and deeply, and lose colour.{{cite journal | last1 = Crawford | first1 = F.T. | year = 1977 | title = Induction and duration of tonic immobility | journal = The Psychological Record | volume = 27 | pages = 89–107 | doi = 10.1007/bf03394435 | s2cid = 149316109 }} A similar behavior has been reported for convict tangs in the field.{{cite journal | last1 = Howe | first1 = J.C. | year = 1991 | title = Field observations of death feigning in the convict tang, Acanthurus triostegus (Linnaeus), with comments on the nocturnal color pattern in juvenile specimens | journal = Journal of Aquariculture and Aquatic Sciences | volume = 6 | pages = 13–15 }}

File:Heterodon platirhinos 2.jpg playing dead and regurgitating a toad]]

==Amphibians and reptiles==

Tonic immobility can be found in several families of anurans (frogs and toads).{{Cite journal|last1=Toledo|first1=Luís Felipe|last2=Sazima|first2=Ivan|last3=Haddad|first3=Célio F.B.|date=2010-07-12|title=Is it all death feigning? Case in anurans|journal=Journal of Natural History|volume=44|issue=31–32|pages=1979–88|doi=10.1080/00222931003624804|bibcode=2010JNatH..44.1979T |s2cid=84462802|issn=0022-2933}} In anurans, tonic immobility is demonstrated most often with open eyes and the limbs sprawled and easy to move, but some species keep their eyes closed. Some species also protrude their tongue.

Tonic immobility has also been observed in several species of lizards and snakes.{{Cite journal|last1=Gregory|first1=Patrick T.|last2=Isaac|first2=Leigh Anne|last3=Griffiths|first3=Richard A|date=2007|title=Death feigning by grass snakes (Natrix natrix) in response to handling by human "predators."|journal=Journal of Comparative Psychology|volume=121|issue=2|pages=123–9|doi=10.1037/0735-7036.121.2.123|pmid=17516791|issn=1939-2087}}{{Cite journal|last1=Santos|first1=Maurício Beux dos|last2=Oliveira|first2=Mauro Cesar Lamim Martins de|last3=Verrastro|first3=Laura|last4=Tozetti|first4=Alexandro Marques|date=2010|title=Playing dead to stay alive: death-feigning in Liolaemus occipitalis (Squamata: Liolaemidae)|journal=Biota Neotropica|volume=10|issue=4|pages=361–4|doi=10.1590/s1676-06032010000400043|issn=1676-0603|doi-access=free|hdl=10183/29497|hdl-access=free}} The most common example of tonic immobility in the latter is the North American hog-nose snake, but it has also been observed in grass snakes. Tonic immobility can be reliably induced in iguanas by a combination of inversion, restraint and moderate pressure. During tonic immobility, there are obvious changes in respiration including a decline in respiration rate, the rhythm becomes sporadic, and the magnitude irregular. The prolonged period of tonic immobility does not seem to be consistent with the fear hypothesis, but could be the result of a period of cortical depression due to increased brain stem activity.{{cite journal|author1=Prestrude, A.M. |author2=Crawford, F.T.|title=Tonic immobility in the lizard, iguana iguana|journal=Animal Behaviour|volume=18|issue=2|year=1970|pages=391–5|doi=10.1016/s0003-3472(70)80052-5}}

Tonic immobility can also be induced in the Carolina anole. The characteristics of this tonic immobility vary as a function of the duration and condition of captivity.{{cite journal|title=Tonic immobility in Anolis carolinensis: Effects of time and conditions of captivity|year=1978|journal=Behavioral Biology|author1=Hennig, C.W |author2=Dunlap, W.P.|volume=23|issue=1|pages=75–86|doi=10.1016/s0091-6773(78)91180-x}} Tonic immobility is also observed in sea turtles.{{Cite journal |last1=Rusli |first1=Mohd Uzair |last2=Wu |first2=Nicholas C |last3=Booth |first3=David T |date=2016 |title=Tonic Immobility in Newly Emerged Sea Turtle Hatchlings |url=https://meridian.allenpress.com/ccb/article-abstract/15/1/143/76187/Tonic-Immobility-in-Newly-Emerged-Sea-Turtle |journal=Chelonian Conservation and Biology |volume=15 |issue=1 |pages=143–7 |doi=10.2744/CCB-1185.1}}

==Chickens==

Tonic immobility can be induced in chickens, but the behavior is more colloquially referred to as hypnosis.{{Cite journal|last1=Gallup|first1=Gordon G.|last2=Nash|first2=Richard F.|last3=Wagner|first3=Alan M.|date=1971|title=The tonic immobility reaction in chickens: Response characteristics and methodology|journal=Behavior Research Methods & Instrumentation|volume=3|issue=5|pages=237–9|doi=10.3758/bf03208389|s2cid=143472517|issn=0005-7878|doi-access=free}}{{Cite journal|last=Gallup|first=Gordon G.|date=1974|title=Genetic influence on tonic immobility in chickens|journal=Animal Learning & Behavior|volume=2|issue=2|pages=145–7|doi=10.3758/bf03199142|s2cid=144313260|issn=0090-4996|doi-access=free}}

Tonic immobility can be induced in chickens through several means, including by gently restraining them on their side, stomach, or back for a short period of time, or by using chalk to draw a line on the ground away from the chicken's beak while restraining them with their head down.{{Cite journal|last1=Gilman|first1=Thelma T.|last2=Marcuse|first2=F. L.|last3=Moore|first3=A. U.|date=1950|title=Animal hypnosis: a study in the induction of tonic immobility in chickens|journal=Journal of Comparative and Physiological Psychology|volume=43|issue=2|pages=99–111|doi=10.1037/h0053659|pmid=15415476|issn=0021-9940}} Chickens have been used in several studies to elucidate the genetic basis of tonic immobility. While early studies focused on determining whether tonic immobility was influenced by genetics, a study in 2019 identified five genes that potentially control tonic immobility in white leghorn chickens and red junglefowl.{{Cite journal|last1=CRAIG|first1=J.V.|last2=KUJIYAT|first2=S.K.|last3=DAYTON|first3=A.D.|date=1984|title=Tonic Immobility Responses of White Leghorn Hens Affected by Induction Techniques and Genetic Stock Differences|journal=Poultry Science|volume=63|issue=1|pages=1–10|doi=10.3382/ps.0630001|pmid=6701136|issn=0032-5791|doi-access=free}}{{Cite journal|last1=Fogelholm|first1=Jesper|last2=Inkabi|first2=Samuel|last3=Höglund|first3=Andrey|last4=Abbey-Lee|first4=Robin|last5=Johnsson|first5=Martin|last6=Jensen|first6=Per|last7=Henriksen|first7=Rie|last8=Wright|first8=Dominic|date=2019-05-07|title=Genetical Genomics of Tonic Immobility in the Chicken|journal=Genes|volume=10|issue=5|pages=341|doi=10.3390/genes10050341 |pmid=31067744|pmc=6562468|doi-access=free}}

==Ducks==

Tonic immobility has been observed in several species of ducks as an effective anti-predatory response. A study by Sargeant and Eberhardt (1975) determined that ducks who feigned death had a better chance at surviving a fox attack than those who resisted and struggled.{{Cite journal|last1=Sargeant|first1=Alan B.|last2=Eberhardt|first2=Lester E.|date=1975|title=Death Feigning by Ducks in Response to Predation by Red Foxes (Vulpes fulva)|journal=American Midland Naturalist|volume=94|issue=1|pages=108|doi=10.2307/2424542|jstor=2424542|bibcode=1975AMNat..94..108S |issn=0003-0031}} Despite being immobile the ducks remained conscious and were aware of opportunities for escape. Although the researchers concluded that tonic immobility was an effective anti-predator response, they conceded that it would not be useful against predators that kill or fatally injure prey immediately after capture.

==Rabbits==

Tonic immobility occurs in both domestic and wild species of rabbit and can be induced by placing and restraining the animal for a short period of time.{{Cite journal|last1=Whishaw|first1=Ian Q.|last2=Previsich|first2=Nick|last3=Flannigan|first3=Kelly P.|date=1978|title=Tonic immobility in feral and domestic dutch rabbits (Oryctolagus cuniculus), mountain cottontail (Sylvilagus nuttalli), and whitetail jackrabbit (Lepus townsendi) as a function of posture|journal=Behavioral Biology|volume=24|issue=1|pages=88–96|doi=10.1016/s0091-6773(78)92941-3|issn=0091-6773}} As in other prey animals, tonic immobility is considered to be an antipredator behavior in rabbits.{{Cite journal|last1=Giannico|first1=Amália Turner|last2=Lima|first2=Leandro|last3=Lange|first3=Rogério Ribas|last4=Froes|first4=Tilde Rodrigues|last5=Montiani-Ferreira|first5=Fabiano|date=2014-02-11|title=Proven cardiac changes during death-feigning (tonic immobility) in rabbits (Oryctolagus cuniculus)|journal=Journal of Comparative Physiology A|volume=200|issue=4|pages=305–310|doi=10.1007/s00359-014-0884-4|pmid=24515628|s2cid=12719656|issn=0340-7594}} Studies on tonic immobility in rabbits focus on the European rabbit Oryctolagus cuniculus, but other species of rabbit have been studied.

A laboratory experiment by Ewell, Cullen, and Woodruff (1981) provided support to the hypothesis that European rabbits use tonic immobility as an anti-predator response.{{Cite journal|last1=Ewell|first1=Albert H.|last2=Cullen|first2=John M.|last3=Woodruff|first3=Michael L.|date=1981|title=Tonic immobility as a predator-defense in the rabbit (Oryctolagus cuniculus)|journal=Behavioral and Neural Biology|volume=31|issue=4|pages=483–9|doi=10.1016/s0163-1047(81)91585-5|issn=0163-1047}} The study found that how quickly the rabbits "righted" themselves (i.e. how quickly they came out of tonic immobility) depended on how far a predator was away from the rabbit, and how close the rabbit was to their home cage. Rabbits that were closer to their home cage righted themselves more quickly than those that were farther from their home cage. Conversely, when predators were closer to the rabbits, they took longer to right themselves. These results were consistent with those found in studies on chickens, lizards, and blue crabs at the time, and provided support that rabbits use tonic immobility as an antipredator response.

A more recent study on European rabbits monitored their heart rate during tonic immobility and found several physiological changes to the cardiovascular system during this state, including a decrease in heart rate.

==Humans==

Tonic immobility has been hypothesized to occur in humans undergoing intense trauma,{{cite journal |vauthors=Magalhaes AA, Gama CM, Gonçalves RM, Portugal LC, David IA, Serpeloni F, Wernersbach Pinto L, Assis SG, Avanci JQ, Volchan E, Figueira I, Vilete LM, Luz MP, Berger W, Erthal FS, Mendlowicz MV, Mocaiber I, Pereira MG, de Oliveira L |title=Tonic Immobility is Associated with PTSD Symptoms in Traumatized Adolescents |journal=Psychol Res Behav Manag |volume=14 |pages=1359–69 |date=2021 |pmid=34512046 |pmc=8420784 |doi=10.2147/PRBM.S317343 |doi-access=free}}{{cite journal |vauthors=Lloyd CS, Lanius RA, Brown MF, Neufeld RJ, Frewen PA, McKinnon MC |title=Assessing Post-Traumatic Tonic Immobility Responses: The Scale for Tonic Immobility Occurring Post-Trauma |journal=Chronic Stress (Thousand Oaks) |volume=3 |pages=2470547018822492 |date=2019 |pmid=32440591 |pmc=7219877 |doi=10.1177/2470547018822492 }} including sexual assault.{{cite journal |last1=Galliano |first1=G. |last2=Noble |first2=L.M. |last3=Travis |first3=L.A. |last4=Puechl |first4=C. |title=Victim reactions during rape/sexual assault: A preliminary study of the immobility response and its correlates |journal=Journal of Interpersonal Violence |volume=8 |issue=1 |pages=109–114 |date=1993 |doi=10.1177/088626093008001008 |url=https://digitalcommons.kennesaw.edu/facpubs/485/}}{{Cite news|url=https://www.washingtonpost.com/news/grade-point/wp/2015/06/23/why-many-rape-victims-dont-fight-or-yell/|title=Why many rape victims don't fight or yell|first=James W.|last=Hopper|newspaper=Washington Post |date=June 23, 2015}}

{{cite journal

| author-link = Kalaf, Juliana et al.

| title = Sexual trauma is more strongly associated with tonic immobility than other types of trauma — A population based study

| journal = Journal of Affective Disorders

| pages = 71–76

| volume = 215

| date = March 7, 2017

| doi = 10.1016/j.jad.2017.03.009

| pmid = 28319694

| last1 = Kalaf

| first1 = Juliana

| last2 = Coutinho

| first2 = Evandro Silva Freire

| last3 = Vilete

| first3 = Liliane Maria Pereira

| last4 = Luz

| first4 = Mariana Pires

| last5 = Berger

| first5 = William

| last6 = Mendlowicz

| first6 = Mauro

| last7 = Volchan

| first7 = Eliane

| last8 = Andreoli

| first8 = Sergio Baxter

| last9 = Quintana

| first9 = Maria Inês

| last10 = De Jesus Mari

| first10 = Jair

| last11 = Figueira

| first11 = Ivan

}}

There is also an increasing body of evidence that points to a positive contribution of tonic immobility in human functioning. Thus, defensive immobilization is hypothesized to have played a crucial role in the evolution of human parent-child attachment,{{cite journal | author = Porges S W | year = 2003 | title = Social engagement and attachment: a phylogenetic perspective | journal = Annals of the New York Academy of Sciences | volume = 1008 | issue = 1| pages = 31–47 | doi=10.1196/annals.1301.004| pmid = 14998870 | bibcode = 2003NYASA1008...31P | s2cid = 1377353 }} sustained attention and suggestibility,{{cite journal |last1=Hoskovec |first1=J |author-link=Jiří Hoskovec |last2=Svorad |first2=D |year=1969 |title=The relationship between human and animal hypnosis |journal=American Journal of Clinical Hypnosis |volume=11 |issue=3 |pages=180–2 |doi=10.1080/00029157.1969.10402029 |pmid=5764620}}{{cite journal |doi= 10.1590/S0047-20852013000400006 | title= Hypnosis, tonic immobility and electroencephalogram |year=2013 |last1=Cortez |first1=C. M. |journal= Jornal Brasileiro de Psiquiatria |volume=62 |issue=4 |pages=285–296 |last2=Silva |first2=D | issn = 0047-2085 |doi-access=free }} REM sleep{{cite journal | author = Tsoukalas I | year = 2012 | title = The origin of REM sleep: A hypothesis | journal = Dreaming | volume = 22 | issue = 4| pages = 253–283 | doi=10.1037/a0030790}} and theory of mind.{{cite journal |doi=10.1007/s40806-017-0112-x |title=Theory of Mind: Towards an Evolutionary Theory |year=2018 |last=Tsoukalas |first=Ioannis |journal= Evolutionary Psychological Science |volume=4 |issue=1 | pages=38–66|doi-access=free }}[https://drive.google.com/file/d/1CCwSs2TrvPwwSU8rDyUkvtLYAuYfylMD/view?usp=sharing Pdf.]

Induction

Tonic immobility is considered to be a fear-potentiated response induced by physical restraint and characterised by reduced responsiveness to external stimulation. It has been used as a measure in the assessment of animal welfare, particularly hens, since 1970.{{cite journal | last1 = Gallup | first1 = G.G. Jr. | last2 = Nash | first2 = R.F. | last3 = Potter | first3 = R.J. | last4 = Donegan | first4 = N.H. | year = 1970 | title = Effect of varying conditions of fear on immobility reactions in domestic chickens (Gallus gullus) | journal = Journal of Comparative and Physiological Psychology | volume = 73 | issue = 3| pages = 442–5 | doi = 10.1037/h0030227 | pmid = 5514679 }}{{cite journal | last1 = Gallup | first1 = G.G. Jr | year = 1979 | title = Tonic immobility as a measure of fear in the domestic fowl | journal = Animal Behaviour | volume = 27 | pages = 316–7 | doi = 10.1016/0003-3472(79)90159-3 | s2cid = 53271327 }}{{cite journal | last1 = Jones | first1 = B. | last2 = Faure | first2 = J.M. | year = 1981 | title = Tonic immobility ("righting time") in laying hens housed in cages and pens | journal = Applied Animal Ethology | volume = 7 | issue = 4| pages = 369–372 | doi = 10.1016/0304-3762(81)90063-8 }} The rationale for the tonic immobility test is that the experimenter simulates a predator, thereby eliciting the anti-predator response. The precept is that the prey animal 'pretends' to be dead to be able to escape when/if the predator relaxes its concentration. Death-feigning birds often take advantage of escape opportunities; tonic immobility in quail reduces the probability of the birds being predated by cats.{{cite journal | last1 = Forkman | first1 = B. | last2 = Boissy | first2 = A. | last3 = Meunier-Salaün | first3 = M.-C. Canali | last4 = Jones | first4 = R.B. | year = 2007 | title = A critical review of fear tests used on cattle, pigs, sheep, poultry and horses | url = https://www.openaccessrepository.it/record/25751| journal = Physiology & Behavior | volume = 92 | issue = 3 | pages = 340–374 | doi = 10.1016/j.physbeh.2007.03.016 | pmid = 18046784 | s2cid = 15179564 }}

To induce tonic immobility, the animal is gently restrained on its side or back for a period of time, e.g. 15 seconds. This is done either on a firm, flat surface or sometimes in a purpose-built V- or U-shaped restraining cradle. In rodents, the response is sometimes induced by additionally pinching or attaching a clamp to the skin at the nape of the neck.{{cite journal | last1 = Zamudio | first1 = S.R. | last2 = Quevedo-Corona | first2 = L. | last3 = Garcés | first3 = L. | last4 = De La Cruz | first4 = F. | year = 2009 | title = The effects of acute stress and acute corticosterone administration on the immobility response in rats | journal = Brain Research Bulletin | volume = 80 | issue = 6| pages = 331–6 | doi = 10.1016/j.brainresbull.2009.09.005 | pmid = 19772903 | s2cid = 24347387 }} Scientists record behaviours such as the number of inductions (15-second restraining periods) required for the animal to remain still, the latency to the first major movements (often cycling motions of the legs), latency to first head or eye movements and the duration of immobility, sometimes called the 'righting time'.

Tonic immobility has been used to show that hens in cages are more fearful than those in pens, hens on the top tier of tiered battery cages are more fearful than those on the lower levels,{{cite journal | last1 = Jones | first1 = R.B. | year = 1987 | title = Fearfulness of caged laying hens: The effects of cage level and type of roofing | journal = Applied Animal Behaviour Science | volume = 17 | issue = 1–2| pages = 171–5 | doi = 10.1016/0168-1591(87)90018-9 }} hens carried by hand are more fearful than hens carried on a mechanical conveyor,{{cite journal | last1 = Scott | first1 = G.B. | last2 = Moran | first2 = P. | year = 1993 | title = Fear levels in laying hens carried by hand and by mechanical conveyors | journal = Applied Animal Behaviour Science | volume = 36 | issue = 4| pages = 337–345 | doi = 10.1016/0168-1591(93)90131-8 }} and hens undergoing longer transportation times are more fearful than those undergoing transport of a shorter duration.{{cite journal | last1 = Cashman | first1 = P. | last2 = Nicol | first2 = C.J. | last3 = Jones | first3 = R.B. | year = 1989 | title = Effects of transportation on the tonic immobility fear reactions of broilers | journal = British Poultry Science | volume = 30 | issue = 2| pages = 211–221 | doi = 10.1080/00071668908417141 }}

Tonic immobility as a scientific tool has also been used with mice,{{cite journal | last1 = Bazovkina | first1 = D.V. | last2 = Tibeikina | first2 = M.A. | last3 = Kulikov | first3 = A.V. | last4 = Popova | first4 = N.K. | year = 2011 | title = Effects of lipopolysaccharide and interleukin-6 on cataleptic immobility and locomotor activity in mice | journal = Neuroscience Letters | volume = 487 | issue = 3| pages = 302–4 | doi = 10.1016/j.neulet.2010.10.043 | pmid = 20974218 | s2cid = 6789654 }} gerbils,{{cite journal | last1 = Griebel | first1 = G. | last2 = Stemmelin | first2 = J. | last3 = Scatton | first3 = B. | year = 2005 | title = Effects of the cannabinoid CB1 receptor antagonist rimonabant in models of emotional reactivity in rodents | journal = Biological Psychiatry | volume = 57 | issue = 3| pages = 261–7 | doi = 10.1016/j.biopsych.2004.10.032 | pmid = 15691527 | s2cid = 18429945 }} guinea pigs,{{cite journal | last1 = Donatti | first1 = A.F. | last2 = Leite-Panissi | first2 = C.R.A. | year = 2011 | title = Activation of corticotropin-releasing factor receptors from the basolateral or central amygdala increases the tonic immobility response in guinea pigs: An innate fear behaviour | journal = Behavioural Brain Research | volume = 225 | issue = 1| pages = 23–30 | doi = 10.1016/j.bbr.2011.06.027 | pmid = 21741994 | s2cid = 1566034 }} rats, rabbits{{cite journal | last1 = Verwer | first1 = C.M. | last2 = van Amerongen | first2 = G. | last3 = van den Bos | first3 = R. | last4 = Coenraad | first4 = F.M.H. | year = 2009 | title = Handling effects on body weight and behaviour of group-housed male rabbits in a laboratory setting | journal = Applied Animal Behaviour Science | volume = 117 | issue = 1–2| pages = 93–102 | doi = 10.1016/j.applanim.2008.12.004 }} and pigs.{{cite journal | last1 = Hessing | first1 = M.J.C. | last2 = Hagelsø | first2 = A.M. | last3 = Schouten | first3 = W.G.P. | last4 = Wiepkema | first4 = P.R. | last5 = van Beek | first5 = J.A.M. | year = 1994 | title = Individual behavioral and physiological strategies in pigs | journal = Physiology and Behavior | volume = 55 | issue = 1| pages = 39–46 | doi = 10.1016/0031-9384(94)90007-8 | pmid = 8140172 | s2cid = 24787960 }}