Autotomy

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White-headed dwarf gecko

Lizard tail autotomy

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Marbled Gecko (Christinus marmoratus) post-autotomy

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Fishing spider autotomy

Autotomy (from the Greek auto- "self-" and tomy "severing") is a behavior whereby an animal sheds or discards one or more of its own appendages, usually as a self-defense mechanism designed to elude a predator's grasp or to distract the predator and thereby allow escape. The term can also be applied in a broader sense to include the shedding of parts of the organism's body that are damaged or diseased.

Mechanisms and Occurrences

Autotomy is most commonly found in invertebrates, such as starfish, crustaceans (e.g., crabs and lobsters), and insects; however, it is also present in some vertebrates, notably among lizards and some mammals (such as certain rodents and marsupials). The mechanisms and complexity of autotomy vary significantly among species. In some cases, the lost body part may be regenerated over time.

Invertebrates

Among invertebrates, autotomy can be seen in several forms. For example, sea cucumbers expel internal organs to distract predators, a process known as evisceration. Starfish may drop arms to escape predators, with the lost limb later regenerating. Many insects, such as certain stick insects and cockroaches, can shed limbs.

Vertebrates

In vertebrates, the most well-known examples are found in lizards, such as the gecko, which can shed its tail when threatened. This process, known as caudal autotomy, involves the breaking off of the tail at a specific pre-formed fracture plane. The tail may continue to wiggle after detachment, serving to distract the predator and allowing the lizard to escape. Some species of rodents and marsupials have also developed the ability to undergo skin autotomy, shedding patches of skin and fur to escape when caught by a predator.

Adaptive Value

Autotomy serves as an adaptive strategy to increase an organism's chances of survival when caught by a predator. By sacrificing a part of its body, the organism can escape and live to reproduce, albeit at a cost. This cost can include the energy and resources needed to regenerate the lost part, reduced mobility, or decreased reproductive success. Therefore, autotomy is generally considered a last resort when other defensive strategies have failed.

Regeneration

The ability to regenerate lost parts varies widely among species that exhibit autotomy. In some, like many lizards, the regenerated tail will not fully replicate the original in appearance or function. In others, such as starfish, the new limb can be almost indistinguishable from the original. The process of regeneration is complex and involves the re-growth of tissues, nerves, and sometimes even bone.

Evolutionary Aspects

The evolution of autotomy as a defense mechanism raises interesting questions about the balance between survival and reproduction. The ability to escape predation by sacrificing a body part must be weighed against the subsequent costs, including the risk of infection, the energy demands of regeneration, and potential reductions in mating success. The widespread occurrence of autotomy across a range of taxa suggests that, in many cases, the benefits outweigh the costs.