Discovery of 'alien' amphibians that can both lay eggs and breastfeed their babies

After studying and observing the Ringed caecilian (Siphonops) , researchers learned that these creatures have unusual methods of caring for their offspring, including milk production and egg laying.

Researchers in Brazil have discovered the first known egg-laying amphibian to feed its young with "milk" . And unlike mammals, this roundworm produces nutrient-rich milk from its tail.

Furthermore, this type of milk also plays a role in supplementing the protein-rich skin that the mother also develops to feed her babies. This discovery is transforming scientific understanding of amphibian reproductive behavior.

All caecilian worms have limited vision and can only distinguish light from dark with their primitive eyes. Although they are called worms, they are, in fact, vertebrates. Their skulls are strong, thick, and pointed, and many of their bones are fused for added rigidity. Their mouths are located further back, under the head, to keep mud from sticking to their teeth, and they have concentric rings of muscle that act like a piston. They can also swim and have sensory spots on their faces that are believed to be used for smelling.

Ringed caecilian (Siphonops) is one of 220 known species of caecilian - a group of limbless amphibians that spend most of their lives underground. Some caecilian species give birth to live young, but there are also subspecies of caecilians that lay eggs.

Carlos Jared, lead author of the study published in the journal Science and a biologist at São Paulo's Butantan Institute, told Popular Science : ' They are one of the least understood amphibians because of their Reaching these animals is very difficult '.

The elusiveness of this organism has made it difficult to discover its ability to produce milk. In fact, without BBC nature series, researchers might not have observed this nematode's unique parenting strategy.

Siphonops worm eggs are laid in a small burrow, in which the mother curls up to protect the eggs. When the young hatch, they begin to lunge at their mother and scrape off her skin with their 44 spoon-shaped teeth. The process took a maddening seven minutes. Between feedings, the mother worm will continuously regenerate her skin and replenish lipids to help her young develop quickly.

More than a decade ago, a film crew working on the 2008 series Life in Cold Blood captured rare footage of a female Ringed caecilian worm with her offspring. The baby amphibian worms went "crazy" , tearing off pieces of their mother's skin. Researchers later discovered that mothers had developed an outer layer filled with this protein to feed their young.

'We were so fascinated by this that we didn't pay much attention to the other behaviors we saw,' study co-author Marta Antoniazzi, another researcher at the Butantan Institute, told Scientific American .

The first footage encouraged researchers to dig deeper into the parenting strategies of the Ringed caecilian. And what they found changed their understanding of this amphibian's behavior.

This worm was originally discovered in Argentina, and has been recorded in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, and Venezuela. Its natural habitats are subtropical or tropical moist lowland forests, dry savanna, moist savanna, subtropical or tropical moist shrubland, and subtropical or tropical moist grassland. or seasonal flooding, grasslands, plantations, rural gardens, and former forests are seriously degraded.

The researchers decided to scrutinize the BBC footage and take note of any other strange behavior. First, they noticed that young worms often keep themselves close to their mother's cloaca - a posterior opening that serves urinary, digestive and reproductive purposes.

'The babies' heads are always near the mother's cloaca,' Jared told Scientific American . Some even poked their heads in and seemed very excited.'

The research team decided to compare the intestines, bladder, cloaca and oviducts of female worms with and without offspring. In the mother's oviduct, they found large glands filled with fatty acids and sugar-rich lactose.

The structure of this 'milk' is very similar to that of mammalian milk. 

Additionally, the researchers discovered that the young wiggled near the cloaca and made high-pitched sounds to encourage the mother to produce milk. This phenomenon can happen up to six times a day. This behavior has never been observed in amphibians before.

Ringed caecilian has an overall length of 28-45 cm and a body diameter of 12-20 mm. The typical lifespan of a Ringed caecilian is 1-2 years. The mouth of roundworms contains dozens of needle-sharp teeth and they swallow food whole. They often eat soil-dwelling invertebrates such as termites, beetle pupae, and mollusks. They can also eat small snakes, frogs, lizards and other worms.

Now, researchers say the findings provide insights into how the worm evolved.