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Christina Miller
Last update: Wednesday, January 16, 2008. |
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A freshly-autotomized tail. Notice the broken blood vessels and exposed bone. The white matter is fat tissue. This is a Leiocephalus schreibersi. |
One of those peculiar herp behaviours that many of us have (unexpectedly) experienced is caudal autotomy. A shocking event to the unaware, most lizards and salamanders can sever their tail when seized, then escape while the tail is left twitching in their wake. Autotomy comes from Greek words meaning "to cut oneself," essentially self-amputation.
Within herps, caudal autotomy can specifically occur in lizards including the iguanids, geckos, and some agamids. Platynotan lizards, most agamids and all chameleons cannot perform this behaviour. In some species, only juveniles may autotomize the tail, and adults cannot (for example the Green Iguana, Iguana iguana). Amphisbaenians may also autotomize, and a few snake species have also been known to perform caudal autotomy. Many caudate amphibians can also perform autotomy. |
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Anatomy and physiology
These species have special anatomical adaptations that allow them to sever their tail and not bleed to death from the trauma.
Lizards and caudates have special weak points in their tail vertebrae called fracture planes, which are unossified sections (bone is not formed along the plane). Etheridge (1967) describes six different forms of lizard caudal vertebrae, each with a different position of the fracture plane. These divisions are present in the muscle and skin, as well. Agamid lizards and snakes possess intervertebral (between two adjacent vertebrae) fracture planes. Rings of muscle encircle these planes, and the animal may constrict the muscles in reponse to a perceived threat to sever the tail. These muscular rings also ligate local blood vessels to prevent bleeding.
Note that the vertebrae closest to the cloaca cannot be autotomized, they are called the non-autotomous pygal series.
Once the tail is dropped, is will proceed to twitch and thrash about, hopefully attracting the predator's attention while the animal escapes.
To better attract the predator's attention, some tails are brightly coloured or are broad and stout to mimic the head. Some species will become completely still except for the tail, that they may wave or undulate so that it stands out.
It is important to note that autotomy is a reflex, an instinctive reaction to a particular stimulus. Some animals have brittle or fragile body parts that will break off easily when grasped, this is not true autotomy.
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Juvenile Five-lined Skinks (Eumeces fasciatus) have a brightly-coloured tail to better attract the attention of a predator. The bright blue fades to grey with age in this species. Photo courtesy of Charles Hannan.
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Regenerated tail on an adult green iguana. This individual lost a portion of its tail as a juvenile, as when Iguana iguana matures, the tail stiffens and will not autotomize. Notice the different colouration and scalation.
Leopard Geckos (Eublepharis macularius) and other lizards from arid environments normally have plump tails that act as a storehouse for fat. Dropping its tail is a big loss for a Leopard Gecko.
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Regeneration
While this defensive behaviour is often effective, it is very costly to the animal. Disadvantages the animal could suffer include:
- Energy loss: The animal will stop growing in body size while the tail regenerates because of the large amount of energy required to regrow a body part. Caudal autotomy is particularly expensive if the species has large fat reserves in its tail.
- Social status and ability to communicate: Animals that lose their tails are likely to hide more and be more conservative with their behaviours. Species that use their tails in social displays, such as Curly-tailed Lizards (Tropiduridae, Leiocephalus) are at a disadvantage with other members of the same species.
- Balance and locomotion: Some arboreal species use their tail for balance, others for locomotion (for example, while swimming). In captivity, these disadvantages are not life-threatening, but in the wild they can be.
It should be noted that males who recently autotomized their tail are less likely to breed, and females that are regrowing a tail should not be bred because of the energy demands of both processes (producing eggs/young, and a tail).
Many species do regenerate the tail, but it will not be exactly the same shape, colour or texture as the original. No new vertebrae are formed, but a rod of stiff cartilage, instead. This mean that the tail can only be dropped "once," since fracture planes were lost (but if only a partial section of the tail was lost originally, the tail may be broken again, closer to the body, and regenerate from that point on). Animals that can regenerate will stop growing in body size until they have regenerated their tail.
Forked tails are an anomaly in regeneration, and occur when an intact or regenerated tail are broken only partially, allowing the original piece to remain while a new portion regenerates from the exposed tissue. Tails that have furcated up to seven times have been recorded! (Ananjeva and Danov, 1991)
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- In captivity
Autotomy usually occurs in captive lizards due to rough handling, but even gentle handling of nervous (often wild caught) individuals may provoke autotomy.
Little intervention is needed for an autotomized tail, because the animal's body takes care of things quite well! No sutures or bandage are needed- sutures can actually interfere with proper healing. If the wound is excessively dirty with substrate or waste material from the cage, it may be rinsed with warm water or a mild antiseptic like 1% Betadine (povidone-iodine) solution. If excessive bleeding occurs, a light temporary pressure bandage may be applied (excessive bleeding of an autotomized tail suggests that the animal may have some illness, as the bleeding typically stops abruptly). Antibiotics are not necessary unless an infection is obvious.
Partially broken tails can either be left to heal, or removed manually (preferably by a veterinarian). Note that this may result in a crooked or bifurcated tail if left to heal on its own.
To prevent caudal autotomy from occuring, be very gentle when handling lizards, and avoid handling nervous, easily stressed specimens when possible. The tail should never be held to restrain the animal.
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