Autotomy and Regeneration: Nature's Bioengineering

Dr Abe V Rotor


Old folks tell us of the magic of lizards growing new tails, crabs regaining lost claws, starfish arising from body pieces. How can we explain the mystery behind these stories?

The biological phenomenon behind these stories is called regeneration. The male deer grows a new set of anthers each year; sea squirts and hydras are produced from tiny buds; the same way plants grow from cuttings. New worms may regenerate from just pieces of the body; and some fish can sprout new fins to replace the ones that have been bitten off.

Experiments demonstrated that the forelimb of a salamander severed midway between the elbow and the wrist, can actually grow into a new one exactly the same as the lost parts.  The stump re-forms the missing forelimb, wrist, and digits within a few months.  In biology this is called redifferentiation, which means that the new tissues are capable of reproducing the actual structure and attendant function of the original tissues.  

Curious the kid I was, I examined a twitching piece of tail, without any trace of its owner. I was puzzled at what I saw.  My father explained how the lizard, a skink or bubuli (photo), escaped its would-be predator by leaving its tail twitching to attract its enemy, while its tailless body stealthily went into hiding.  “It will grow a new tail,” father assured me. I have also witnessed tailless house lizards (butiki) growing back their tails at various stages, feeding on insects around a ceiling lamp. During the regeneration period these house lizards were not as agile as those were with normal tails, which led me to conclude how important the tail is.

Regeneration is a survival mechanism of many organisms. Even if you have successfully subdued a live crab you might end up holding only its pinchers and the canny creature has gone back into the water. This is true also to grasshoppers; they escape by pulling away from their captors, leaving their large trapped hind legs behind. But soon, like their crustacean relatives, new appendages will start growing to replace the lost ones.

Another kind of regeneration is compensatory hypertrophy, a kind of temporary growth response that occurs in such organs as the liver and kidney when they are damaged. If a surgeon removes up to 70 percent of a diseased liver, the remaining liver tissues undergo rapid mitosis (multiplication of cells) until almost the original liver mass is restored. Similarly, if one kidney is removed, the other enlarges greatly to compensate for its lost partner. ~