An amphibian discovered that takes care of its eggs and suckles its young

Textbooks say there are two main groups of amphibians.

They are not lying, anurans, those without tails (frogs, toads...) and caudates, with tails (salamanders and newts) represent the majority of this class of animals.

But there is a third order, that of the gymnofiones, or caecilians, which live in humid equatorial and subtropical areas.

The school textbooks highlight that they are all oviparous and do not usually take care of their young or feed them.

However, in Brazil, under cocoa crops, a caecilian has been discovered that does not abandon its eggs and that, when they hatch, feeds its young with a whitish liquid rich in fats and sugars until they fully develop.

Breastfeeding seems to be not exclusive to mammals.

There is another difference with frogs or salamanders, male caecilians use an organ called phallodeum, similar to a penis, for internal fertilization, when in other amphibians it is external.

The enormous reproductive plasticity of amphibians is completed in gymnophyans with the existence of oviparous species, in which embryonic development occurs inside the eggs, and other viviparous species, which feel their young grow inside them, in the oviduct.

The

Siphonops annulatus

is one of the 39 species that exist in Brazil.

To European eyes it looks like a worm, although in America they are called blind snakes.

In their evolution and adaptation to the environment, they lost, in addition to their sight, their legs.

But they developed tentacles with a network of mechanoreceptors and chemoreceptors that make up for the lack of the other senses.

It is oviparous, but does not abandon its eggs after laying.

He stays with them, surrounds them with his body and waits.

More information

The fungus that is exterminating frogs

“In 2006 we saw that as soon as it was born it fed its offspring with its own skin,” recalls Carlos Jared, a scientist at the Butantan Institute, the main research and production center for serums and vaccines in Brazil.

“It seemed impossible.

You saw them so alert, so active, growing so fast, eating only once or twice a week,” he adds.

The offspring of

S. annulatus

grow up to 135% in their first week out of the egg.

Marta Antoniazzi, also from the Butantan Institute, points out that “this substance, which is very nutritious, only appears on the skin during reproduction time.”

These caecilians are lead blue in color, but once the eggs are laid they begin to turn white.

“They acquire a whitish color because they have many lipid droplets within the cells of the epidermis of the skin.

And the babies feed on the last layer of the skin, which usually changes every week,” she adds.

This strange case of dermatophagy was so interesting that

Nature

, the most prestigious scientific magazine, published the research in 2006. Even Sir David Attenborough and a BBC team traveled to the Atlantic forest in the state of Bahia to see these creatures and their mysterious way of eating.

“They used very sophisticated equipment, such as endoscopic cameras.

They introduced them into the animals' nest and saw that the babies passed through the sewer many times,” Jared recalls.

In amphibians, but also in birds, reptiles and most fish, the cloaca is an exit hole shared by the reproductive, excretory and digestive systems.

But the documentary did not clarify how the hatchlings could survive on that food source alone.

“We hypothesized that

S. annulatus

offspring could be nourished by some additional substance provided by the mother, in addition to the skin,” says Pedro Mailho, who is doing his doctorate with Jared.

“We were based on the suspicion that the skin provided, which is produced once a week on average, would not be sufficient to explain the enormous massive growth of the offspring.”

Furthermore, “we sporadically surprised them touching the opening of the maternal cloaca with their mouths and apparently also making chewing movements,” he adds.

They decided to record what happened in the nest during the two months of parental care, “trying to fit one more piece into the eccentric reproductive biology of the caecilians,” concludes the researcher.

After laying the eggs, these caecilians take care of them until they hatch.

During this time they go from lead blue to a whitish gray.

It is the 'milk' with which they will feed their young for two months. Carlos Jared

After hundreds of hours of recording, “we were able to observe that the babies were feeding several times a day through milk released through the maternal cloacal opening,” says Mailho.

The details of this discovery have just been published in the journal

Science

, with Mailho as first author, and Antoniazzi and Jared as co-authors.

Several of these nests were taken to the laboratory to study them thoroughly.

The first thing was to analyze the whitish liquid secreted by the mother.

For the most part they are lipids, long-chain fatty acids.

In particular, palmitic and stearic acid represent 98.61%.

Other nutrients they identified were proteins from the mother's own skin and carbohydrates.

In comparison, cow's milk is 32.6% palmitic acid and 8.7% stearic acid.

Another 11.6% is myristic acid, also present in this caecilian, but in smaller quantities.

What feeds them cannot be called milk because they are not mammals and do not have mammary glands, but they do have glands.

When studying the oviduct, the Butantan researchers discovered a series of glands made up of atrophied epithelial cells.

And it is from them that this type of milk emerges.

They also discovered that the mother released her on demand.

“Provisioning seemed to be stimulated not only by the contact of the pups' snouts in the cloacal opening, but also by the sounds they emitted,” details Mailho.

“These sounds are variable and sound similar to high-frequency, repetitive clicks or squeals.”

In this there is no difference with beings of other orders, such as mammals.

British zoologist Mark Wilkinson began his research career with Jared and Antoniazzi with the discovery that these caecilians fed from their mother's skin.

Now at the Natural History Museum in London (United Kingdom), he believes that “this beautiful work demonstrates the nutritious nature of this liquid, its importance for offspring and its origin in the oviducts.”

For this amphibian expert “each new example of lactation provides comparative information that can help us understand the evolution of this trait.”

But he doesn't think the story ends there: "Caecilians are very little known, so we won't be able to be sure until we do a lot more work to uncover the secrets of their reproductive biology."

You can follow

MATERIA

on

Facebook

,

X

and

Instagram

, or sign up here to receive

our weekly newsletter

.