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Autotomy

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Introduction

  • Cause: defensive response of lizards and some snakes to predator attack that can also occur with inappropriate handling.
  • Signs: part or all of the tail is spontaneously shed.
  • Diagnosis: clinical signs.
  • Treatment: monitoring, preventing infection.
  • Prognosis: usually very good.
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Presenting signs

  • Tail has been shed leaving behind a clean wound, usually with minimal or no hemorrhage.
  • Owners may have observed the autotomy event.
  • Autotomy may be deliberately employed by veterinary surgeons for the purposes of tail amputation.

Acute presentation

  • The tail is shed during handling.
  • The autotomized tail continues to move immediately after being shed for up to 30 min.

Age predisposition

  • Younger more skittish individuals may be more likely to shed their tails.

Breed/Species predisposition

  • 13 of the 20 described lizard families can perform autotomy. The ones most commonly seen in practice include Lacertidae (true lizards), Anguidae (legless lizards), Geckonidae (geckos) and Iguanidae (iguanas).
  • The following families do not perform autotomy:
    • Chamaeleontidae (true chameleons), Agamidae (Agamas, Bearded dragons etc), Helodermatidae (Gila monsters), Xenosauridae (Knob scaled lizards), and Varanidae (Monitor lizards)
  • The tuatara, a lizard-like reptile and the only member of its order, is also capable of autotomy.
  • A very small number of snake species also perform autotomy. These are generally not kept in captivity and are very unlikely to be seen in practice.

Pathogenesis

Etiology

  • Certain lizard families have developed caudal autotomy as a defense against predators.
  • When the tail is grasped by a predator or by inappropriate human handling, the lizard can shed it. This may also happen without direct contact if an animal is threatened.
  • The threshold for autotomy not only varies with the species but also with the locality where they originate, and the species of predator that is likely to attack them. It is likely that captive bred animals that are handled more frequently are less likely to perform autotomy.
  • Autotomy occurs at pre-formed fracture planes that allow the vertebral column to separate alongside the adjacent musculature, nerves, blood vessels and skin. In most lizard species these fracture planes are intra-vertebral although in a minority they are inter-vertebral.
  • Muscle contraction around the fracture planes facilitates the autotomy by breaking the bone along the fracture plane and by providing hemostasis (this is why more force is required to amputate a tail via a fracture plane when an animal is anesthetized Tail amputation).
  • The shed tail can then thrash or wriggle independently for up to 30 min by utilizing anaerobic metabolism. This is designed to distract predators while the lizard escapes.
  • In most lizard species capable of autotomy, the autotomized tail will regenerate. The new tail is often less vivid in coloration and the demarcation between the old and new sections is usually apparent. The regenerated tail contains cartilage rather than ossified bone .
  • Autotomy is costly for the individual animal as significant adipose reserves are often found in the tail:
    • In addition, the tail may be used for communication and social or reproductive displays.
    • Regeneration also requires increased energy intake.
    • Free-ranging or wild individuals that have lost their tail are less likely to survive than those which possess one.
    • From a veterinary point of view, systemically unwell animals that are already compromised animals may be further compromised by loss of the tail.
  • Some species may return to eat the shed tail once the threat has passed.

Predisposing factors

General

  • Being caught by a predator.
  • Tail grasping by owners or veterinary staff.
  • Blood sampling the ventral venous sinus/tail vein.
  • Restraint Handling/restraint of young skittish animals.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Bateman P W, Fleming P A & Bateman P W (2009) To cut a long tail short: a review of lizard caudal autotomy studies carried out over the last 20 years. J Zool 277 (1), 1-14 WileyOnline.
  • Dyer S M & Cervasio E L (2008) An overview of restraint and blood collection techniques in exotic pet practice. Vet Clin North Am Exotic Anim Pract 11 (3), 423-443 PubMed.
  • Clause A R & Capaldi E A (2006) Caudal autotomy and regeneration in lizards. J Exper Zool Part A: Comp Exper Biol 305A (12), 965–973 WileyOnline.
  • McConnachie S & Whiting M J (2003) Costs associated with tail autotomy in an ambush foraging lizard, Cordylus melanotus melanotus. African Zool 38 (1), 57–65 TaylorFrancisOnline.
  • Lock B A (2000) Nonreproductive surgery in reptiles. Vet Clin North Am Exotic Anim Pract 3 (3), 715–732 PubMed.

Other sources of information

  • Mader D R et al (2006) Surgery, Reptile Medicine and Surgery. 2nd edn. Elsevier Saunders, USA. pp 581-630.