Have you ever tried catching a lizard with your bare hands? If you have, you will know the pain of missing them after thousands of attempts and holding its tail in your hand, wriggling like a worm. Many types of animals including lizards have an ability to amputate its own appendages (external body parts) as a self-defence mechanism.This behaviour is called autotomy, coming from the Greek words auto, “self” and tome, “severing”.

 

Why do they cut their tails?

 

Lizards are best-known users of autotomy. They are a group of squamate reptiles, with over 7,000 species. Except for some lizards such as the green iguana or bearded dragon, which are some of the most common lizards that people keep as pets, most lizards are capable of “dropping” their tails in an emergency situation and regrowing it

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    Green Iguana                                              Bearded dragons 

 

So, why do they drop their own tails? In nature, lizards are in the lower part of the food chain, meaning they're always at risk of getting hunted by predators. Lots of predators reside in the forests and deserts and it is an extremely vulnerable environment for lizards. Therefore, lizards have developed amputation for their survival advantage. After the amputation, the nerve in its tail remains for a while and its wiggly motion confuses the predators and gives them some time to escape. Many species of lizards have the colour and pattern on the tail that is designed to make it more visible than the body of the lizard. Plestiodon fasciatus, commonly known as the five lined skink, has bright blue tails. This attracts the predator's attention to its tail, away from its body and head that are not regrowable.This allows the predators to go after the tail rather than other parts of the body that will be critical to the lizard’s survival.

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How do they cut their tail? 

 

Vertebrae in a lizard’s tail are ringed by muscles that fit together like plugs and sockets, with each conical “plug” covered in microscopic bumps and “sockets” that connects the plug to the body, allowing lizards to detach its tail easily. When the lizards want to detach its tail, they bend their tails at a side angle rather than by yanking straight back. By this motion, the tail is 17 times more likely to fracture from bending than from being pulled. The lizards twisted their tails to cleanly cleave them in two along the fleshy fracture plane. Losing the tail does not seriously harm a lizard or hurt them severely. It is a motion of detachment of the body part that is led by itself.

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How do they regrow the tail? 

 

Studies have shown that lizards aid the process of autotomy by contracting muscles around the fracture planes. As their “plug” is detached from its body, the socket contracts its muscle to heal the cut. During this process, its muscle and fat create a new tail that can be detached again for emergency uses. These regenerated tails are often not as long as the original and less aesthetic (change in pattern). Regenerated tails are made of cartilage instead of bone, but they can also be broken off and carry its functions. It is not uncommon to find lizards in the wild with no tail or with a partially regenerated tail, however the tail of lizards normally grows fully for its locomotion and balance that is significant to their survival.

 

 

 

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The top photograph shows a marbled gecko, a lizard native to Australia. The change in pattern on the tail indicates regeneration of its tail after autotomy. Also, the bottom photograph shows House Gecko that has regrown bifurcated tails. This often happens to lizards in the process of regrowing their tail and the most amount of tail regrown recorded was six.

 

Effect on lizards

 

Autotomy not only gives lizards better opportunities for survival but also other advantages. This is clearly shown in Agama lizards. Agama lizards fight by using their tail as whips. By dropping tails, they lose their ability to fight with other males. This decreases their mating ability and dominance in their society. However, as the tail autotomises, it gets a club-like shape, making it a better fighting weapon. 

Despite those benefits, losing a tail can be very costly to lizards. In nature, lizards are exposed to an environment full of mites, parasites and other insects. As the tail loss weakens the lizard’s immune system, numerous infections may happen and this can lead to possible death. Lizard dropping its tail may seem like a trivial behaviour to us as it can regrow; However, this can be a life-threatening event for lizards. Next time we see a lizard, let’s leave them to chill under the sunlight.

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By Yoochan Hwang