Scientists find worms that recently evolved the ability to regrow a complete head

New study reveals regeneration of amputated body parts is not always an ancient trait and scientists might need to rethink the way they compare animals with regenerative abilities

An international group of researchers including biologists found that at least four species of marine ribbon worms independently evolved the ability to regrow a head after amputation.

Regeneration of amputated body parts is uncommon but does exist throughout the animal world–from salamanders, spiders and sea stars that can regrow appendages to a species of ribbon worm that can regenerate an entire individual from just a small sliver of tissue. But regenerative abilities were broadly assumed to be an ancient trait that some species managed to hold on to while most others lost through evolution.

This new study, which was published in Proceedings of the Royal Society B, turns that assumption on its head. In a survey of 35 species of marine ribbon worms, the researchers found that the ability to regenerate an entire head, including a brain, evolved relatively recently in four different species.

“This means that when we compare animal groups we cannot assume that similarities in their ability to regenerate are old and reflect shared ancestry,” said Alexandra Bely, associate professor of biology at UMD and one of the study’s authors. “We need to be more careful when comparing regeneration findings across different groups of animals.”

All animals have some degree of regenerative ability. Even humans re-grow damaged skin over a wound. However, animal lineages that diverged very early in evolutionary history–such as sponges, hydroids and ctenophores–are often able to regrow entire individuals from even small amputated parts. As animals evolved greater complexity, regenerative abilities have become less dramatic and common.

This new research presents the clearest documentation of animals gaining regenerative abilities and could shed light on the characteristics necessary for the trait to evolve.

Research article: A phylum-wide survey reveals multiple independent gains of head regeneration in Nemertea

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