An amphibian makes it too : NPR

Caecilians are amphibians that superficially resemble very large earthworms. New research suggests that at least one species of caecilian also produces “milk” for its young.

Photo by Carlos Jared

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Photo by Carlos Jared

Caecilians are amphibians that superficially resemble very large earthworms. New research suggests that at least one species of caecilian also produces “milk” for its young.

Photo by Carlos Jared

A species of worm-like amphibian has been caught on camera feeding milk to its young.

The creature, known as a caecilian, lives underground. Researchers believe the animal has evolved the ability to produce a milky substance, independent of mammals, which are commonly known for feeding milk to their young.

Caecilians are descended from the same lineage as frogs and salamanders. Hundreds of millions of years ago, their ancestors dug deep into the ground. They lost their legs, their eyes largely stopped working, and their bodies became long and segmented. A modern caecilian looks a bit like a long glittering earthworm with a head, leading some to call them icky.

That’s a characterization that Marta Antoniazzi completely rejects.

“I really don’t agree that they are disgusting,” says Marta Antoniazzi, a biologist at the Instituto Butantan in Sao Paulo, Brazil. Brazil is home to many caecilians and Antoniazzi is a fan.

“They are quite elegant, have a shiny body and a very beautiful face,” she says.

But wait, there’s more.

The specific caecilian species that Antoniazzi and her colleagues are studying is named Siphonops annulatus. Mothers of this species give birth to broods of squirmy babies, which then eat their own mother’s skin off.

“Once a week they can eat her skin,” said Pedro Luiz Mailho-Fontana, a researcher at the Insituto Butantan who was involved in the study.

Mom doesn’t seem to be bothered by this, and the babies get a lot of nutrition from the skin.

Carlos Jared heads the institute’s structural biology department and leads the team that studied the caecilians. As he watched this fascinating process, he noticed that the squirmy babies had a lot of energy.

“They are so active that it is impossible to eat only once or twice a week,” he says.

So the team placed a camera in the nest and started watching. And soon they noticed that the babies were gathering around a certain spot.

“The babies prefer to go to the mother’s tail,” he says.

And then they saw it. A discharge from the tail: “Some kind of substance, like milk.”

Upon further investigation, the team found that the milk contained lipids and sugars similar to those found in mammals. It provided essentially the same function.

“It’s a very unusual form of nutrition” for an egg-laying animal, Mailho-Fontana says.

The team published their results this week in the Journal Science.

Marvalee Wake, a professor of integrative biology at the University of California at Berkeley, who was not involved in the research, says this species of caecilian evolved to address a similar problem faced by human babies. Just like humans, the little ones are born long before they can take care of themselves. They are vulnerable. And to help them grow while still keeping them close, their mother has developed a milky fluid.

“This is convergent evolution,” she says.

Convergent evolution is the process by which very different species can develop similar traits.

But is it really milk?

The Brazilian team does not say whether the milk meets FDA standards, but it does contain lipids and sugars. Wake says she thinks it counts.

“If it has all these basic subunits, it’s convergent evolution on a food material, and that’s what it’s all about,” she says.

For Antoniazzi, caecilians are a wonderful reminder that very different animals, such as puppies and subterranean worm amphibians, can have a lot in common.

“Nature is very creative,” she says. “Sometimes it gives the same solution for different groups of animals.”

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