Decapitated worms repel their brains

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For some species of worms, decapitation is not serious: they only develop a new head.

But far from being an ancestral skill, a recent study suggests that this ability is a relatively recent adaptation, at least in terms of evolution.

Regeneration is unusual in animals, but species that can do so are scattered throughout the animal kingdom and include starfish, hydras, fish, frogs, salamanders and spiders, as well as worms. The regeneration of body parts has long been considered an ancestral trait, and various animals have traced the capacity of a distant common ancestor that probably emerged hundreds of millions of years ago.

However, for some species of marine tapeworms, the ability to regrow heads and cut brains dates back to only 10 to 15 million years ago, making it a much more recent adaptation than the current one. we did not think before, have discovered scientists. [In Photos: Worm Grows Heads and Brains of Other Species]

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As part of this study, researchers compiled data on 35 species of tapeworms of the phylum Nemertea, cutting heads and tails of individuals belonging to 22 species. They discovered that all species could repel an amputated tail, "but surprisingly, few people could regenerate a complete head," wrote the study's scientists. (However, all the grubs have survived for weeks or months after their decapitation.)

Five species of worms have been documented: spotted heads and brains repelling: four of them have observed it for the first time, and one that was previously known for the regeneration of the head. In addition, researchers have found additional evidence in earlier studies of head growth in three other species of worms.

Their results show that the ancestor of all tapeworms probably could not repel a severed head, and that growth of the head appeared independently in only a few species of worms. This also raises important questions about all animals that can regenerate parts of the body, the researchers wrote.

"When we compare animal groups, we can not assume that the similarities in their ability to regenerate are old and reflect shared ancestry," said study co-author Alexandra Bely. , an associate professor of biology at the University of Maryland, in a statement.

The results were published online on March 6 in Proceedings of the Royal Society B.

Originally published on Science live.