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When they are born, baby caecilians (legless amphibians that look like a mix of a snake and a worm) use their tiny hooked teeth to scrape their mother’s skin and feast. The flakes are dead but extra fatty and nutrient-dense, and within three months the babies have grown into independent teenagers.
Habit offers more than food. According to a study published in maySkin feeding allows mothers to pass on their unique microbiomes and possibly inoculate the immune system of their offspring, the first known case of microbiome transmission between amphibians.
“It’s a remarkably strange thing,” he said. David Blackburn curator of herpetology at the Florida Museum and author of the study. “When you cut open their stomach, guess what: They have skin on their stomach.” He added: “It’s really important to understand what microbes are, where they come from and what their interactions with diseases are.”
As for amphibians, caecilians are eccentric: they have no legs, their eyes are tiny and sometimes covered in skin, and they perceive their surroundings with two small tentacles on their faces. Very few amphibians are known to care for their children (most species of frogs and salamanders tend to lay eggs and leave once they are born), but caecilians have evolved in sophisticated ways. parenting strategies.
Some give birth to fully formed young that have already eaten the skin from their mother’s oviduct; others care for their eggs and then donate an outer layer of skin to their newborn offspring. It’s not clear which of these behaviors evolved first, Dr. Blackburn said, nor is it clear to what extent they help offspring survive.
For weeks, Dr. Blackburn’s team dug through the rainforest floors of southeastern Cameroon and eventually collected 29 skin-feeding caecilians of the species Herpele squalostoma. The researchers analyzed and sequenced 1.5 million microbial DNA sequences from the skin and intestines of caecilians (six adult males, nine adult females (three of them mothers), and 14 juveniles) and 5,000 DNA sequences from microbes in the environment. surrounding.
Few of the bacteria found in the offspring matched those recovered from nearby leaves, water and soil. But in some offspring, up to 20 percent of their microbiome matched that of their mother’s skin or gut microbe communities.
“For 20 years I thought, ‘It must have something to do with immunity!’” he said. Carlos Jared, director of the Structural Biology Laboratory of the Butantan Institute of Brazil and renowned caecilian hunter. He was not involved in this study, but he has also been researching the relationship between parenthood and microbiome transfer, and was glad that his two-decade-long intuition had found some confirmation.
“It’s an example of reproductive ecology that has consequences for unrelated aspects of biology,” he said. Marcos Wilkinson, evolutionary biologist at the Natural History Museum, London. In 2006, Dr. Wilkinson published the first description of skin feeding behavior, and found that the skin of caecilian mothers was twice as thick as that of adult females without offspring. “They’re kind of lactating,” she said.
All of the researchers emphasized that the findings were very preliminary, based on a small sample and with many unanswered questions. Are there peak periods when the microbiome of young people is assembled? Does it start growing soon after birth or does it accumulate over a long period of care?
Some species of caecilians are poisonous, and it is unclear what happens to the toxins when the young consume the skin. It is also unknown whether this mode of microbial transfer exacerbates transmission of skin diseases that have been plaguing amphibians and could pose a threat to caecilians.
But learning anything about caecilians is a headache, as they spend most of their time underground, Dr Blackburn said: “Caecilians have been around for more than 200 million years, but we know very little about their biology. real”.
As a result, he added, it is difficult to know to what extent the lessons from caecilians can be applied to amphibians in general.
“Here’s a group of animals that just does things in a fundamentally different way to all other amphibians, but they’re sort of lumped in with frogs and salamanders,” Dr Blackburn said. “But it would be like lumping whales in with horses.”