Autotomy in Animals: Here's Why Some Creatures Shed Parts, Grow Them Back

Several lizards and snakes can voluntarily shed or discard their tails. This process is actually known as autotomy.

What Is Autotomy?

Autotomy, or self-amputation, is a defense mechanism to an attack that involves amputating or actively breaking a body part. This ability is exhibited by several creatures, such as crickets, walking sticks, grasshoppers, and salamanders. It is typically a mechanism for self-preservation and is managed by hormones or nerves.

Prey could intentionally drop a body part in order to keep a predator distracted and eventually escape. However, if the animal successfully escapes, it may end up in a vulnerable condition as the lost body part regrows. Due to the high costs of autotomy, it only exists in species where it is a highly effective strategy for escape and could help with the organisms life or death.

Probably the most well-known case of shedding tails is done by anole lizards.

The most dramatic case happens in Elysia sea slugs, which are capable of shedding their entire body and grow another one in a matter of three weeks. They could be doing it in order to rid themselves of parasites inside. Such a feat is possible even if a digestive system is lacking, as slugs have photosynthetic algae that produce food with sunlight.

Repair and Regeneration

On top of having self-amputating abilities, several animals can also replace and regrow their lost limbs. Regeneration, which refers to the complete or partial replacement of the appendage that is lost, could end up offsetting several possible long-term autotomy costs.

While all animals are capable of regeneration, the extent varies from species to species. The capacity to regenerate is usually limited among species that have elaborated bodies, though bony fish are capable of replacing their spinal cords while salamanders can regrow their limbs. There are also some simple creatures, such as Hydra and flatworms, that can regenerate their bodies from small fragments across their lifespan.

As an organism ages, it ends up becoming less capable of having complex structures, such as an appendage or organ, replaced. Even among younger creatures, regeneration capabilities vary throughout the body. It is difficult to replace the joints and the heart due to their constant use. However, blood cells, liver, and skin can continually get replaced.

As for how limbs regrow, scientists have dug deeper into this intricate process by taking body parts away and studying their replacement growth. For instance, after the leg of a salamander is amputated, molecules exit the cells that were ruptured while the stump is covered by an epidermis. This attracts stem cells to the wound. These cells end up forming a blastema, which is a mass of tissues that are embryo-like. It then turns into a limb bud and morphs gradually into a new leg.

That said, stem cells are mainly responsible for regeneration. Though most fully developed adult tissues have specialized roles, stem cells are capable of producing various cell types.

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