Autotomy (from the Greek auto- "self-" and tome "severing", αὐτοτομία) or self-amputation is the behaviour whereby an animal sheds or discards one or more of its own appendages, usually as a self-defense mechanism to elude a predator's grasp or to distract the predator and thereby allow escape. Some animals have the ability to regenerate the lost body part later.
Reptiles and amphibians
Some lizards, salamanders and tuatara when caught by the tail will shed part of it in attempting to escape. In many species the detached tail will continue to wriggle, creating a deceptive sense of continued struggle, and distracting the predator's attention from the fleeing prey animal. Depending upon the species, the animal may be able to partially regenerate its tail, typically over a period of weeks or months. Though functional, the new tail section often is shorter and will contain cartilage rather than regenerated vertebrae of bone, and in colour and texture the skin of the regenerated organ generally differs distinctly from its original appearance.
The technical term for this ability to drop the tail is caudal autotomy. In most lizards that sacrifice the tail in this manner, breakage occurs only when the tail is grasped with sufficient force, but some animals, such as some species of geckos, can perform true autotomy, throwing off the tail when sufficiently stressed, such as when attacked by ants.
Caudal autotomy in lizards takes two forms. In the first form, called intervertebral autotomy, the tail breaks between the vertebrae. The second form of caudal autotomy is intravertebral autotomy, in which there are zones of weakness, fracture planes across each vertebra in the mid-part of the tail. In this second type of autotomy the lizard contracts a muscle to fracture a vertebra, rather than break the tail between two vertebrae. Sphincter muscles in the tail then contract around the caudal artery to minimize bleeding. Caudal autotomy is prevalent among lizards; it has been recorded in 13 of approximately 20 families.
Caudal autotomy is present as an anti-predator tactic but is also present in species that have high rates of intraspecific competition and aggression. For example, the Agama agama lizard fights by using its tail as a whip against other conspecifics. It can autotomize its tail but this is met with a social cost - tail loss decreases social standing and mating ability. However, the regenerated tail in this species takes on a new club-like shape providing the male with a better fighting weapon, such that autotomy and regeneration work together to increase the lizards ability to survive and reproduce.
Despite this mechanism’s effectiveness, it is also very costly and is employed only after other defenses have failed. One cost is to the immune system: tail loss results in a weakened immune system which allows for mites and other harmful organisms to have a larger negative impact on individuals and reduce their health and lifespan. Since the tail plays a significant role in locomotion and energy storage of fat deposits, it is too valuable to be dropped haphazardly. Many species have evolved specific behaviors after autotomy, such as decreased activity, in order to compensate for negative consequences such as depleted energy resources. Some such lizards, in which the tail is a major storage organ for accumulating reserves, will return to a dropped tail after the threat has passed, and will eat it to recover part of the sacrificed supplies. Conversely, some species have been observed to attack rivals and grab their tails, which they eat after their opponents flee. Regeneration is one of the highest priorities after autotomy, in order to optimize locomotor performance and recoup reproductive fitness. While regenerating their tails, caudal autotomy is restored at an energetic cost that often hinders body growth or intraspecies interactions.
Autotomy in the fossil record
Fossils of reptiles possessing the ability to autotomize that are not within the lizard family have been found that date back to the late Carboniferous and Early Permian Era. Two squamate species from the Jurassic period, Eichstaettisaurus schroederi and Ardeosaurus digitatellus, were identified as having intervertebral autotomy planes, and these species were placed in the squamate taxonomy as being an ancestor of current existing geckos.
At least two species of African spiny mice, Acomys kempi and Acomys percivali, are capable of autotomic release of skin, e.g. upon being captured by a predator. They are the first mammals known to do so. They can completely regenerate the autotomically released or otherwise damaged skin tissue — regrowing hair follicles, skin, sweat glands, fur and cartilage with little or no scarring. It is believed that the corresponding regeneration genes could also function in humans.
Over 200 species of invertebrates are capable of using autotomy as an avoidance or protective behaviour. These animals can voluntarily shed appendages when necessary for survival. Autotomy can occur in response to chemical, thermal and electrical stimulation, but is perhaps most frequently a response to mechanical stimulation during capture by a predator. Autotomy serves either to improve the chances of escape or to reduce further damage occurring to the remainder of the animal such as the spread of a chemical toxin after being stung.
Autotomy occurs in some species of octopus for survival and for reproduction: the specialized reproductive arm (the hectocotylus) detaches from the male during mating and remains within the female's mantle cavity.
Species of (land) slugs in the genus Prophysaon can self-amputate a portion of their tail. There is known autotomy of the tail of sea snail Oxynoe panamensis under persistent mechanical irritation.
Some sea slugs exhibit autotomy. Both Discodoris lilacina and Berthella martensi will often drop their entire mantle skirt when handled, leading to Discodoris lilacina also being called Discodoris fragilis. The members of Phyllodesmium will drop a large number of their cerata each, on the tip having a large sticky gland that secretes a sticky substance.
Autotomic stone crabs are used as a self-replenishing source of food by humans, particularly in Florida. Harvesting is accomplished by removing one or both claws from the live animal and returning it to the ocean where it can regrow the lost limb(s). However, under experimental conditions, but using commercially accepted techniques, 47% of stone crabs that had both claws removed died after declawing, and 28% of single claw amputees died; 76% of the casualties died within 24 hours of declawing. The occurrence of regenerated claws in the fishery harvest is low; one study indicates less than 10%, and a more recent study indicates only 13% have regenerated claws. (See Declawing of crabs)
Post-harvest leg autotomy can be problematic in some crab and lobster fisheries, and often occurs if these crustaceans are exposed to freshwater or hypersaline water in the form of dried salt on sorting trays. The autotomy reflex in crustaceans has been proposed as an example of natural behaviour that raises questions concerning assertions on whether crustaceans can "feel pain", which may be based on definitions of "pain" that are flawed for lack of any falsifiable test, either to establish or deny the meaningfulness of the concept in this context.
Under natural conditions, orb-weaving spiders (Argiope spp.) undergo autotomy if they are stung in a leg by wasps or bees. Under experimental conditions, when spiders are injected in the leg with bee or wasp venom, they shed this appendage. But, if they are injected with only saline, they rarely autotomize the leg, indicating it is not the physical injection or the ingress of fluid per se that causes autotomy. In addition, spiders injected with venom components which cause injected humans to report pain (serotonin, histamine, phospholipase A2 and melittin) autotomize the leg, but if the injections contain venom components which do not cause pain to humans, autotomy does not occur.
Bees and wasps
Sometimes when honey bees (genus Apis) sting a victim, the barbed stinger remains embedded. As the bee tears itself loose, the stinger takes with it the entire distal segment of the bee's abdomen, along with a nerve ganglion, various muscles, a venom sac, and the end of the bee's digestive tract. This massive abdominal rupture kills the bee. Although it is widely believed that a worker honey bee can sting only once, this is a partial misconception: although the stinger is barbed so that it lodges in the victim's skin, tearing loose from the bee's abdomen and leading to its death, this only happens if the skin of the victim is sufficiently thick, such as a mammal's. The sting of a queen honey bee has no barbs, however, and does not autotomize. All species of true honey bees have this form of stinger autotomy. [clarify] Two wasp species that use sting autotomy as a defense mechanism are Polybia rejecta and Synoeca surinama.
The endophallus and cornua portions of the genitalia of male honey bees (drones) also autotomize during copulation, and form a mating plug, which must be removed by the genitalia of subsequent drones if they are also to mate with the same queen. The drones die within minutes of mating.
- (2000). The American Heritage Dictionary of the English Language: Fourth Edition.
- Congdon, J.D.; Vitt, L.J.; King, W.W. (1974). "Geckos: adaptive significance and energetics of tail autotomy". Science. 184 (4144): 1379–1380. doi:10.1126/science.184.4144.1379.
- Kelehear, C.; Webb, J.K. (2006). "Effects of tail autotomy on anti-predator behavior and locomotor performance in a nocturnal gecko". Copeia. 2006 (4): 803–809. doi:10.1643/0045-8511(2006)6[803:eotaoa]2.0.co;2.
- Wilson, R.S.; Booth, D.Y. (1998). "Effect of tail loss on reproductive output and its ecological significance in the skink Eulamprus quoyii". Journal of Herpetology. 32 (1): 128–131. doi:10.2307/1565493. JSTOR 1565493.
- Chapple, D.G.; McCoull, C.J.; Swain, R. (2002). "Changes in reproductive investment following caudal autotomy in viviparous skinks (Niveoscincus metallicus): lipid depletion or energetic diversion?". Journal of Herpetology. 36 (3): 480–486. doi:10.2307/1566193. JSTOR 1566193.
- Lin, Z.; Qu, Y.; Ji, X. (2006). "Energetic and locomotor costs of tail loss in the Chinese Skink, Eumeces chinensis". Comparative Biochemistry and Physiology. 143A (4): 508–513. doi:10.1016/j.cbpa.2006.01.018. PMID 16488639.
- Bellairs, A.D., and Bryant, S.V., (1985). Autotomy and regeneration in reptiles. In: Biology of the Reptilia. Vol. 15. C. Gans and F. Billet (eds.). John Wiley and Sons, New York. pp. 301–410
- Cooper, W.E. (2003). "Shifted balance of risk and cost after autotomy affects use of cover, escape, activity, and foraging in the Keeled Earless Lizard (Holbrookia propinqua)". Behavioral Ecology and Sociobiology. 54 (2): 179–187. doi:10.1007/s00265-003-0619-y. JSTOR 25063251.
- Dial, B.E.; Fitzpatrick, L.C. (1981). "The energetic costs of tail autotomy to reproduction in the lizard Coleonyx brevis (Sauria: Gekkonidae)". Oecologia. 51 (3): 310–317. doi:10.1007/bf00540899.
- Maiorana, V.C. (1977). "Tail autotomy, functional conflicts and their resolution by a salamander". Nature. 265 (5594): 533–535. doi:10.1038/265533a0.
- Ducey, P.K.; Brodie, E.D.; Baness, E.A. (1993). "Salamander tail autotomy and snake predation: role of antipredator behavior and toxicity for three neotropical Bolitoglossa (Caudata: Plethodontidae)". Biotropica. 25 (3): 344–349. doi:10.2307/2388793. JSTOR 2388793.
- Marvin, A.G. (2010). "Effect of caudal autotomy on aquatic and terrestrial locomotor performance in two Desmognathine salamander species" (PDF). Copeia. 3 (3): 468–474. doi:10.1643/cp-09-188. Archived from the original (PDF) on 2013-12-02.
- Cree, A. (2002). Tuatara. In: Halliday, Tim and Adler, Kraig (eds.), The New Encyclopedia Of Reptiles and Amphibians. Oxford University Press, Oxford, pp. 210–211. ISBN 0-19-852507-9
- Higham, Timothy E.; Russell, Anthony P. (2010). "Flip, flop and fly: modulated motor control and highly variable movement patterns of autotomized gecko tails". Biology Letters. 6 (1): 70–73. doi:10.1098/rsbl.2009.0577. PMC 2817253. PMID 19740891.
- Balasubramanian, D. (2019-03-17). "The lost tail that wags research tales". The Hindu. ISSN 0971-751X. Retrieved 2019-03-25.
- Bely, Alexandra E. (2010-10-01). "Evolutionary Loss of Animal Regeneration: Pattern and Process". Integrative and Comparative Biology. 50 (4): 515–527. doi:10.1093/icb/icq118. ISSN 1540-7063.
- Rose, Walter; The Reptiles and Amphibians of Southern Africa; Pub: Maskew Miller, 1950
- Bateman, P.W.; Fleming, P.A. (2009). "To cut a long tail short: a review of lizard caudal autotomy studies carried out over the last 20 years" (PDF). Journal of Zoology. 277: 1–14. doi:10.1111/j.1469-7998.2008.00484.x.
- Clause, Amanda R.; Capaldi, Elizabeth A. (2006-12-01). "Caudal autotomy and regeneration in lizards". Journal of Experimental Zoology Part A: Comparative Experimental Biology. 305A (12): 965–973. doi:10.1002/jez.a.346. ISSN 1552-499X. PMID 17068798.
- Gans, Carl; Harris, Vernon A. (1964-09-10). "The Anatomy of the Rainbow Lizard Agama agama L.". Copeia. 1964 (3): 597. doi:10.2307/1441541. ISSN 0045-8511. JSTOR 1441541.
- Arnold, E.N. (February 1984). "Evolutionary aspects of tail shedding in lizards and their relatives". Journal of Natural History. 18 (1): 127–169. doi:10.1080/00222938400770131. ISSN 0022-2933.
- Bateman, P. W.; Fleming, P. A. (January 2009). "To cut a long tail short: a review of lizard caudal autotomy studies carried out over the last 20 years". Journal of Zoology. 277 (1): 1–14. doi:10.1111/j.1469-7998.2008.00484.x. ISSN 0952-8369.
- Arnold, E. N. (1984-02-01). "Evolutionary aspects of tail shedding in lizards and their relatives". Journal of Natural History. 18 (1): 127–169. doi:10.1080/00222938400770131. ISSN 0022-2933.
- Brock, Kinsey M.; Bednekoff, Peter A.; Pafilis, Panayiotis; Foufopoulos, Johannes (2015-01-01). "Evolution of antipredator behavior in an island lizard species, Podarcis erhardii (Reptilia: Lacertidae): The sum of all fears?". Evolution. 69 (1): 216–231. doi:10.1111/evo.12555. ISSN 1558-5646. PMID 25346210.
- Argaez, Víctor; Solano-Zavaleta, Israel; Zúñiga-Vega, J. Jaime (2018-04-24). "Another potential cost of tail autotomy: tail loss may result in high ectoparasite loads in Sceloporus lizards". Amphibia-Reptilia. 39 (2): 191–202. doi:10.1163/15685381-17000156. ISSN 0173-5373.
- Clark, DR (1971). "Strategy of Tail-Autotomy in Ground Skink, Lygosoma laterale". Journal of Experimental Zoology. 176 (3): 295–302. doi:10.1002/jez.1401760305. PMID 5548871.
- Durrell, Gerald. My Family and Other Animals. Penguin Books 1987. ISBN 978-0140103113
- Bely, Alexandra E.; Nyberg, Kevin G. (2010-03-01). "Evolution of animal regeneration: re-emergence of a field". Trends in Ecology & Evolution. 25 (3): 161–170. doi:10.1016/j.tree.2009.08.005. PMID 19800144.
- van der Vos, W.; Witzmann, F.; Fröbisch, N. B. (2017-11-16). "Tail regeneration in the Paleozoic tetrapod Microbrachis pelikani and comparison with extant salamanders and squamates". Journal of Zoology. 304 (1): 34–44. doi:10.1111/jzo.12516. ISSN 0952-8369.
- LeBlanc, A. R. H.; MacDougall, M. J.; Haridy, Y.; Scott, D.; Reisz, R. R. (2018-03-05). "Caudal autotomy as anti-predatory behaviour in Palaeozoic reptiles". Scientific Reports. 8 (1): 3328. doi:10.1038/s41598-018-21526-3. ISSN 2045-2322. PMC 5838224. PMID 29507301.
- Simões, Tiago R.; Caldwell, Michael W.; Nydam, Randall L.; Jiménez-Huidobro, Paulina (September 2016). "Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes". Zoological Journal of the Linnean Society. doi:10.1111/zoj.12487. ISSN 0024-4082.
- Seifert, A. W.; Kiama, S. G.; Seifert, M. G.; Goheen, J. R.; Palmer, T. M.; Maden, M. (2012). "Skin shedding and tissue regeneration in African spiny mice (Acomys)". Nature. 489 (7417): 561–565. doi:10.1038/nature11499. PMC 3480082. PMID 23018966.
- Cormier, Zoe (2012-09-26). "African spiny mice can regrow lost skin". Nature. Retrieved 2012-09-27.
- Fleming, P.A.; Muller, D.; Bateman, P.W. (2007). "Leave it all behind: a taxonomic perspective of autotomy in invertebrates". Biological Reviews. 82 (3): 481–510. doi:10.1111/j.1469-185X.2007.00020.x. PMID 17624964.
- McDonnel, R.J., Paine, T.D. and Gormally, M.J., (2009). Slugs: A Guide to the Invasive and Native Fauna of California. 21 pp., ISBN 978-1-60107-564-2, page 9.
- Lewin, R. A. (1970). "Toxin secretion and tail autotomy by irritated Oxynoe panamensis (Opisthobranchiata: Sacoglossa)"" (PDF). Pacific Science. 24: 356–358.
- Rudman, W.B. (October 14, 1998). "Autotomy". The Sea Slug Forum. Archived from the original on 2010-06-15.
- Gulf and Florida Stone Crabs
- Gary E. Davis; Douglas S. Baughman; James D. Chapman; Donald MacArthur; Alan C. Pierce (1978). Mortality associated with declawing stone crabs, Menippe mercenaria (PDF). US National Park Service. Report T-522.
- "The 2006 Stock Assessment Update for the Stone Crab, Menippe spp., Fishery in Florida". Florida Fish and Wildlife Conservation Commission. Retrieved 23 September 2012.
- Davidson, G.W. and Hosking, W.W. (2004) Development of a Method for Alleviating Leg Loss During Post-harvest Handling of Rock Lobsters Archived 2016-03-05 at the Wayback Machine. 104 pp.
- Rose, JD; Arlinghaus, R; Cooke, SJ; Diggles, BK; Sawynok, W; Stevens, ED; Wynne, CDL (2012). "Can fish really feel pain?". Fish and Fisheries. 15: 97–133. doi:10.1111/faf.12010.
- Eisner, T.; Camazine, S. (1983). "Spider leg autotomy induced by prey venom injection: an adaptive response to 'pain'?". Proceedings of the National Academy of Sciences of the United States of America. 80 (11): 3382–3385. doi:10.1073/pnas.80.11.3382. PMC 394047. PMID 16593325.
- Snodgrass, R.E. (1956). The Anatomy of the Honey Bee. Ithaca, New York: Cornell University Press.
- Visscher, P.K.; Vetter, R.S. & Camazine, S. "Removing bee stings". Retrieved April 23, 2013.
- "Why do honeybees die after they sting you?". Retrieved April 23, 2013.
- How Bees Work – howstuffworks.com. Retrieved 23 April 2013.
- Steinau, R. (2011). "Bee stings". Retrieved April 23, 2013.
- Hermann, Henry (1971). "Sting Autotomy, a defensive mechanism in certain social Hymenoptera". Insectes Sociaux. 18 (2): 111–120. doi:10.1007/bf02223116.
- Collins, A.M.; Caperna, T.J.; Williams, V.; Garrett, W.M.; Evans, J.D. (2006). "Proteomic analyses of male contributions to honey bee sperm storage and mating". Insect Molecular Biology. 15 (5): 541–549. doi:10.1111/j.1365-2583.2006.00674.x. PMC 1847503.
- Patrick Flammang; Jerome Ribesse; Michel Jangoux (2002-12-01). "Biomechanics of adhesion in sea cucumber cuvierian tubules (Echinodermata, Holothuroidea)". Integrative and Comparative Biology. 42 (6): 1107–15. doi:10.1093/icb/42.6.1107. PMID 21680394. Archived from the original on 2007-10-14. Retrieved 2008-12-22.
- O'Hara, Timothy; Byrne, Maria (2017). Australian Echinoderms: Biology, Ecology and Evolution. Csiro Publishing. pp. 282–285. ISBN 978-1-4863-0763-0.
- Edmondson, C. H. (1935). "Autotomy and regeneration of Hawaiian starfishes" (PDF). Bishop Museum Occasional Papers. 11 (8): 3–20.
- Pakarinen, E (1994). "Autotomy in arionid and limacid slugs". Journal of Molluscan Studies. 60 (1): 19–23. doi:10.1093/mollus/60.1.19.
- Autotomy in sea gastropod
- The dictionary definition of autotomy at Wiktionary