If you cut a twig off a tree, after a while new branch will emerge by the wounded spot. If you put the broken branch in soil, it will slowly grow into another tree. Such “magical” regeneration power is possessed by most plants. Humans, on the other hand, lack such power. However, quite a few members of the animal world do possess such “magical” power. When part of their body is lost, a new one can be regenerated which is equivalent to the original in terms of appearance and function. What an amazing capacity this is!
The secret behind such “regeneration” of animals is that upon being harmed, a blastema – a mass of cells also known as a regeneration bud – will grow out from the wound. This can then develop into different types of cells such as bone, blood vessels, nerves and cartilage, and eventually build up the lost part. This capacity was discovered in 1740 on hydra, an aqueous invertebrate. Afterwards, scientists identified such “magic” on a variety of animals including arthropods such as spiders, crabs, lobsters as well as non-parasitic flatworms and zebrafish.
It is widely known that geckos can regenerate their tails after losing them. You may have even heard a terrifying rumour that when a gecko is caught it will break its tail and, the broken tail will get into the ear of a person nearby. This is only partly true. In reality the chance of the tail getting into the ear is very low. But it is true that gecko will shed its tail when threatened. This is a self-defence mechanism called “autotomy”. It is to attract the attention of the enemy by the twitching broken tail, while the gecko can escape. After a while, a new tail will grow.
Some starfish can survive amputation. Usually when a starfish encounters danger it will sacrifice an arm, which can regrow later. In Hong Kong, Common Starfish (Archaster typicus) has strong regenerative power and new arms can regrow in a short period of time – and sometimes two or three new arms will be regenerated, so that you may see Common Starfish with six or seven arms. Asterias spp. can even regrow from a single arm and one-fifth of the central disc, back into a whole starfish.
When an earthworm is cut into two parts, what will happen? There is a saying that only the part with the head can survive while some say that each part can turn into a separate earthworm. Both are possible, depending on the species, position of the cut and whether the cut is clear. Research has found that a new head and tail can be regenerated, and the earthworm can survive regardless of whether it loses its head or tail. Therefore, an earthworm broken into two parts can become two new earthworms, or in some cases, can turn into earthworms with two heads or two tails! How intriguing!
All amphibians, particularly those with a tail, have the ability to regenerate their body parts. Mexican Axolotl (Ambystoma mexicanum) is supreme in terms of regeneration. It can regrow its brain, eyes, heart and legs, and even if all four legs are paralysed it can still regenerate the nerves and ability to move again!
Afrian Spiny Mouse
In recent years, scientists have found regenerative power in African Spiny Mouse (Acomys spp.). This is the first time such an ability has been identified in mammals. When caught by a predator, it will undergo autotomy and shed a large piece of its fur and part of the ear to escape, and the lost parts can regrow later. Quite different from humans, the hair follicle, skin and cartilage of African Spiny Mouse can all be regenerated, so no scar will remain.
Scientists have also identified some genes related to regeneration of animals. The case of African Spiny Mouse brings exciting news. Maybe we humans will achieve such “magical” regenerative power someday!