A number of years in the past, Sayaka Mitoh, a Ph.D. candidate at Nara Women’s University in Japan, was perusing her lab’s huge assortment of sea slugs when she stumbled upon a ugly sight. One of the lab’s captive-raised sea slugs, an Elysia marginata, had in some way been decapitated.
When Ms. Mitoh peered into its tank to get a greater look, she seen one thing much more stunning: The severed head of the creature was transferring across the tank, munching algae as if there was nothing uncommon about being a bodiless slug.
Ms. Mitoh additionally noticed indicators that the ocean slug’s wound was self-inflicted: It was as if the ocean slug had dissolved the tissue round its neck and ripped its personal head off. Self-amputation, referred to as autotomy, isn’t unusual within the animal kingdom. Having the power to jettison a physique half, similar to a tail, helps many animals keep away from predation. However, no animal had ever been noticed ditching its whole physique.
“I was really surprised and shocked to see the head moving,” mentioned Ms. Mitoh, who research the life historical past traits of sea slugs. She added that she anticipated the slug “would die quickly without a heart and other important organs.” But it not solely continued to stay, it additionally regenerated everything of its misplaced physique inside three weeks.
This prompted Ms. Mitoh and her colleagues to conduct a sequence of experiments aimed toward determining how and why some sea slugs guillotine themselves. The outcomes of their experiments, published Monday in Current Biology, present proof that Elysia marginata, and a carefully associated species, Elysia atroviridis, purposefully decapitate themselves with a view to facilitate the expansion of a brand new physique. Although extra analysis is required, the researchers suspect these sea slugs ditch their our bodies once they develop into contaminated with inside parasites.
Ms. Mitoh and her staff monitored a number of teams of Elysia marginata and Elysia atroviridis over the course of the creatures’ lives. Not all the ocean slugs they monitored decapitated themselves, however many did — one even did it twice. Bodies regenerated from the heads of each species, however the headless our bodies stayed headless. However, these dumped our bodies reacted to stimuli for so long as months, earlier than decomposing.
The head wounds the ocean slugs created throughout autotomy took solely someday to heal. Organs similar to the guts took a mean of 1 week to regenerate. For many of the sea slugs, the regeneration course of took lower than three weeks to finish.
“We’ve known for a long time that sea slugs have regenerative capabilities, but this really goes beyond what we had thought,” mentioned Terry Gosliner, senior curator of invertebrate zoology on the California Academy of Science.
Dr. Gosliner, who has found over one-third of all sea slug species recognized to exist, suspects that the spectacular regenerative functionality of those sea slugs could relate to a different spectacular organic expertise they possess.
Elysia marginata and Elysia atroviridis are sometimes known as “solar-powered sea slugs.” They are amongst a small variety of slugs that may incorporate chloroplasts from the algae they eat into their our bodies. This lets the slugs maintain themselves, not less than partially, on the sugars the chloroplasts produce by way of photosynthesis.
Having this means, which is named kleptoplasty, might be what permits these sea slugs to outlive lengthy durations of time with out their our bodies.
In most animals and even some sea slugs, autotomy is believed to serve solely as a way of avoiding predation. But the researchers discovered proof that it will also be used to expel inside parasites. All of the Elysia atroviridis that separated their heads had inside parasites, in line with the researchers. And by ditching their infested our bodies, they efficiently expelled them, regenerating parasite-free types. Parasites weren’t present in any of the Elysia marginata.
Whatever goal, these sea slugs’ regenerative talents are “remarkable,” mentioned Kenro Kusumi, a biologist at Arizona State University who research regeneration in reptiles. According to Dr. Kusumi, the ocean slugs in query have all the perfect traits present in animals able to advanced regeneration. For instance, these sea slugs have a “breakage plane” alongside their necks that enables for a clear break. Many lizards, including geckos, have an identical breakage aircraft close to the bottom of their tail.
“It’s so interesting to see so many features of regeneration in the animal kingdom brought together in one organism,” Dr. Kusumi mentioned.
Much stays to be realized about drivers and organic mechanisms that permit Elysia marginata and Elysia atroviridis to sever their very own heads and regenerate their our bodies, however Ms. Mitoh and different scientists imagine that enhancing our understanding of this unusual phenomenon might someday result in advances in regenerative drugs and different fields.
Until the solar-powered slugs’ secrets and techniques are revealed, Ms. Mitoh will proceed spending her days watching her beloved sea slugs behead themselves. It’s grisly work, however somebody has to do it.