Motherhood takes many forms. Most vertebrates, such as birds, reptiles, amphibians, and fish, reproduce by laying eggs filled with nutritious yolk that their offspring use as an initial source of nutrition before hatching. Mammals change the rules of the game by giving birth to live young and feeding them fatty, sugary milk as they stand.
But nature continually breaks the rules, and the last animals to confuse one yolk with another. milk rails are caecilians, the egg-laying, legless amphibians that look like worms. Published research On Thursday, in the journal Science, it is suggested that they also feed their young with a substance similar to milk, but from the bottom. This behavior is unknown in amphibians.
This heightens the curiosity of caecilians, who are already known to feed their young skin torn from their mother’s back as a nutritious post-natal snack.
“It’s like they’re from another planet,” he said Carlos Jared, Cecilian researcher at the Butantan Institute in Sao 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 much of their lives underground, they are hard to find and even harder to study.
Since 1987, his team has been thinking about milk production by caecilians. After several trips to cocoa plantations in the Atlantic Forest of Brazil, his team managed to collect 16 mothers of the caecilian species Siphonops annulatus and their numerous young. Each mother has four to 13 children. Back in the lab, they filmed each family during the two months from hatching until the amphibious worms became independent.
Each mother never left her litter, not even to feed, and the babies wriggled on her back and rubbed up against the ends of her body. It is here that the little ones enthusiastically compete to gnaw a white and viscous liquid coming from the maternal cloaca, sticking their heads almost inside it.
Puppies suck this milk several times a day, reaching 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 caecilian mother, they found that it was fatty and rich in carbohydrates, just like mammalian milk.
Basically, the videos show baby caecilians energetically sliding towards their mother, then making high-pitched sounds as they appear to beg for this milk-like substance.
“They cry, they make sounds, click click click click, it’s like begging behavior,” she said Pedro L. Mailho-Fontana also from the Butantan Institute, which covered the hours of video.
Milk-feeding and this type of communication between parents and young have not been found in other amphibians.
“It’s very unique,” Dr. Mailho-Fontana said. Milk-feeding could boost the puppy’s microbiome and immune system, as in humans. Since not all of the hundreds of caecilian species lay eggs – some give birth to live pups that have already scraped the mother’s skin with their small hooked teeth from inside the uterus – his impression is that this strange combination of egg-laying and milk production is an evolutionary step to move from one birthing method to another.
“Evolution happens in different and non-linear ways,” Dr. Mailho-Fontana said.
Or maybe Cecilia moms are just loving parents who use different feeding techniques, according to Marvalee Wakeprofessor 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 not yet clear whether any other caecilian species is doing the same, and how, why, when or where this amphibian milk evolutionarily came from, Dr. Wake said.
There are a variety of reproductive techniques and “totally strange” life histories in the amphibian world, he said David Blackburn, curator of the herpetology department at the Florida Museum of Natural History, who was not involved in the study. Sometimes they’re so strange, though, that it takes science a long time to completely piece them together. The species, he added, was first identified in 1822. “So it only took 200 years, that’s right, more than 200 years to discover it,” Dr Blackburn said. “The Cecilias continue to surprise”.
He wonders about the other 200 or so caecilian species out there.
“OK, now we have skin eating and cloacal milk,” Dr. Blackburn said. “What else is there?”
