Autotomy – Wikipedia, the free encyclopedia

Autotomy (from the Greek auto- "self-" and tome "severing") or self amputation is the behaviour whereby an animal sheds or discards one or more of its own appendages,[1] usually as a self-defense mechanism to elude a predator's grasp or to distract the predator and thereby allow escape. The lost body part may be regenerated later.

Some geckos,[2][3]skinks,[4][5][6]lizards,[7][8][9]salamanders[10][11][12] and tuatara [13] that are captured by the tail will shed part of the tail structure and thus be able to flee. 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. The animal can partially regenerate its tail, typically over a period of weeks. The new section will contain cartilage rather than regenerating vertebrae of bone, and the skin of the regenerated organ generally differs distinctly in colour and texture 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.[14] 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.[15] Conversely, some species have been observed to attack rivals and grab their tails, which they eat after their opponents flee.[16]

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.[17]Sphincter muscles in the tail then contract around the caudal artery to minimize bleeding.

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.[18] 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.[19]

Over 200 species of invertebrates are capable of using autotomy as an avoidance or protective behaviour[20][21] including:

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.[22] There is known autotomy of the tail of sea snail Oxynoe panamensis under persistent mechanical irritation.[23]

Evisceration, the ejection of the internal organs of sea cucumbers when stressed, is also a form of autotomy, and they regenerate the organ(s) lost.[27]

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.[28]

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Autotomy - Wikipedia, the free encyclopedia