Snake-like, worm-like mothers make milk for their babies

Motherhood takes many forms. Most vertebrates, such as birds, reptiles, amphibians, and fish, reproduce by laying eggs filled with a nutritious yolk that their offspring use as a primary source of nutrition before hatching. Mammals change the game by giving birth to their young and feeding them fatty, sugary milk when they get back on their feet.

But nature breaks the rules all the time, and the latest animals to confuse two-yolk with milk are caecilians, legless, egg-laying amphibians that look like worms. Published research They also feed their young a milk-like substance, but from their buttocks, he suggests Thursday in the journal Science. This behavior is unknown in amphibians.

It heightens the curiosity of caecilians, who were already known to feed their young skin torn from their mother's back as a nutritious snack after birth.

“It's like they're from another planet,” he said. Carlos Jared, a snake researcher at the Butantan Institute in São Paulo, Brazil, and author of the study. “For me, they are like Martians.”

Caecilians are “one of the least understood vertebrates,” Dr. Jared said. Because they spend most of their lives underground, they are difficult to find and even more difficult to study.

Since 1987, his team has been thinking about whether caecilians make milk. After several trips to cocoa plantations in Brazil's Atlantic Forest, his team collected 16 caecilian mothers, Siphonops annulatus, and their numerous young. Each mother has from four to 13 children. Back in the lab, they photographed each family during the two months from hatching to the independence of the worm amphibians.

Each mother never left her droppings, not even to feed them, and the young ones writhed on her back, breathing breathless to the ends of her body. This is where the offspring enthusiastically compete to chomp down the sticky white liquid from the mother's cloaca, almost sticking their heads inside it.

The puppies suck this milk several times a day, and grow to more than double their size in the first week. When pharmacologists examined the substance, which is produced in special glands in the oviduct of the mother caecilian, they found that it is fatty and rich in carbohydrates, just like mammalian milk.

More importantly, the videos show the baby caecilians forcefully gliding over the mother, then making high-pitched clicking sounds as they appear to demand the milk-like substance.

“They cry, they make noises, they click click click click, it's like begging behavior,” he said. Pedro L. Mailho Fontana Also from the Butantan Institute, who pored over hours of video.

Breastfeeding and this type of communication between parents and young are not found in other amphibians.

“It's very unique,” ​​Dr. Milo Fontana said. Milk feeding can stimulate the microbiome and immune system of hatchlings, as is the case in humans. Since not all of the hundreds of species of caecilians lay eggs, some give birth to live young that have already scraped the mother's skin with their tiny hooked teeth from inside the womb, his hunch is that this strange combination of egg-laying and also milk production is an evolutionary step in moving from one mode of birth to another. .

“Evolution occurs in different, non-linear ways,” said Dr. Milo Fontana.

Or snake mothers may simply be doting parents using different feeding techniques, according to Marvali Weekprofessor of integrative biology at the University of California, Berkeley, who was not involved in the study.

But these findings are just a starting point: It's still unclear whether any other species of caecilians do this, and how, why, when and where this amphibian milk came from in evolutionary terms, Dr. Wick said.

He said there are a variety of reproductive techniques and life histories that are “completely alien” in the amphibian world. David Blackburn, curator of herpetology at the Florida Museum of Natural History, who was not involved in the study. Sometimes they are very strange, although science takes a long time to completely put them together. He added that this species was first identified in 1822. “It only took us 200 years, didn't it, more than 200 years to discover it,” Dr. Blackburn said. “The caecilians continue to surprise.”

He wonders what other 200 species of caecilians are out there.

“Well, now we have skin nutrition and entrained milk,” Dr. Blackburn said. “What else is there?”