Why some lizards snap off their own tails, and what it costs them
Grab a skink by the tail and you may be left holding a twitching decoy while its owner scuttles away. Dropping a body part to escape a predator, called autotomy, has evolved at least nine separate times. It saves lives, but the bill for the lost tail arrives later in fat, status and health.
The Belgian physiologist Léon Fredericq coined the word in 1883, from Greek roots meaning self-severing. Lizards, salamanders, snakes and tuatara all practise it with their tails, and lizards do it most: caudal autotomy has been recorded in 13 of roughly 20 lizard families. Several species, including the five-lined skink, sport vivid blue tails that steer attacks away from the head and body, while the shed tail keeps writhing to hold a predator's attention.
Many lizards have a fracture plane running across each vertebra in the middle of the tail. Rather than the tail snapping between bones, the lizard contracts a muscle to crack a vertebra, then clamps sphincter muscles around the tail artery to limit bleeding while flaps of skin fold over the wound. Most species only let go under a firm grip, but some geckos throw off the tail on their own when stressed enough, for instance when swarmed by ants. A regrown tail is usually shorter, supported by cartilage instead of bone, and looks different; some salamanders manage a perfect copy, and the western fence lizard sometimes grows a forked one.
Because the tail stores fat and aids movement, animals drop it only when other defences fail. Afterwards the immune system weakens, activity drops, and social life can suffer: side-blotched lizards lose rank, and one Iberian rock lizard mates less often. Some lizards come back to eat their own discarded tail to recover the reserves. A toxic salamander, Bolitoglossa rostrata, holds on to its tail until a predator works its jaws far up it, betting that its poison will do the job first.
The trick is ancient, with fossils of autotomising reptiles going back to the Late Carboniferous. It is not limited to reptiles either. Two African spiny mice, Acomys kempi and Acomys percivali, can shed patches of skin when seized, the first mammals known to do so, and then regrow skin, hair follicles and sweat glands with little scarring.
Source: Autotomy
