A few years ago, Sayaka Mitoh, a Ph.D. candidate at Nara Women’s University in Japan, was reading her lab’s large collection of sea snails when she came across a gruesome face. One of the sea snails kept in the laboratory, an Elysia marginata, was somehow beheaded.
When Mitoh peeks into his tank for a better look, she notices something even more shocking: the severed head of the creature moves into the tank and suffocates algae as if there is nothing unusual about the disembodied snail.
Me. Mitoh also saw signs that the sea snail’s wound had been inflicted itself: it was as if the sea snail had dissolved the tissue around its neck and ripped off its own head. Self-amputation, known as autotomy, is not uncommon in the animal kingdom. If you have the ability to spur a body part, such as a tail, it helps many animals to avoid predators. However, no animal was ever observed that shed its entire body.
“I was really surprised and shocked when I saw the head move,” said Mrs. Mitoh said, studying the life history of sea snails.. She added that she expected the nude to “die quickly without a heart and other vital organs.” But not only did it continue to live, it also recovered the whole of its lost body within three weeks.
This has me. Mitoh and her colleagues encouraged to conduct a series of experiments aimed at finding out how and why some sea snails themselves guillotine. The results of their experiments, published Monday in Current Biology, provide evidence that Elysia marginata, and a closely related species, Elysia atroviridis, purposefully decapitates themselves to facilitate the growth of a new body. Although more research is needed, the researchers suspect that these sea snails engulf their bodies when they become infected with internal parasites.
Me. Mitoh and her team monitored several groups of Elysia marginata and Elysia atroviridis through the course of the creatures’ lives. Not all sea snails they watched beheaded, but many did – one even did it twice. Bodies recovered from the heads of the two species, but the headless bodies remained headless. However, these shed bodies responded to stimuli for as long as months before dissolving.
The head wounds caused by the sea snails during autotomy took only one day to heal. Organs such as the heart took an average of one week to regenerate. For most marine snails, the regeneration process took less than three weeks to complete.
“We have known for a long time that sea snails have regenerative abilities, but it really goes beyond what we thought,” said Terry Gosliner, senior curator of invertebrate zoology at the California Academy of Science.
Dr. Gosliner, who has discovered more than one-third of all water snails, suspects that the impressive resilience of these sea snails may be related to another impressive biological talent they possess.
Elysia marginata and Elysia atroviridis is called “solar-powered sea snails”. They are among a small number of snails that can absorb chloroplasts of the algae they eat into their bodies. This allows the nude snail, at least in part, to maintain the sugars that the chloroplasts produce through photosynthesis.
This ability, known as kleptoplasty, may be what allows these sea snails to survive long periods without their bodies.
In most animals and even some sea snails it is thought that autotomy only serves as a way to avoid predators. But the researchers found evidence that it can also be used to repel internal parasites. All of the Elysia atroviridis that separated their heads had internal parasites, according to the researchers. And by expelling their infected bodies, they successfully expelled them and regenerated parasite-free forms. Parasites were not found in any of the countries Elysia marginata.
Whatever the purpose, the regenerative abilities of these sea snails are “remarkable,” said Kenro Kusumi, a biologist at Arizona State University who studies regeneration in reptiles. According to dr. Kusumi has the sea snails involved the best traits found in animals that can complicate regeneration. These sea snails, for example, have a ‘breaking level’ along their necks that allows a clean break. Many lizards, including geckos, have a similar breaking level near the base of their tail.
“It is so interesting to see that so many features of rebirth in the animal kingdom are merged into one organism,” said dr. Kusumi said.
Much remains to be learned about drivers and biological mechanisms that allow Elysia marginata and Elysia atroviridis to chop off their own heads and regenerate their bodies, but me. Mitoh and other scientists believe that improving our understanding of this strange phenomenon could one day lead to advances in regenerative medicine and other fields.
Until the secrets of solar power are revealed by solar power, Ms. Mitoh spends her days decapitating her beloved sea snails. It’s cruel work, but someone has to do it.