Soon after being born, elusive, worm-like amphibians called caecilians use their teeth to scrape off pieces of their mother’s mucus-coated skin and devour it.
“It’s a remarkably weird thing,” David Blackburn, curator of herpetology at the Florida Museum, tells Sofia Quaglia of the New York Times. “When you open up their stomachs, guess what: They have skin in their stomach.”
The babies spend several weeks with mom, subsisting on these chunks—along with secretions from her cloaca—until they’re large enough to venture out on their own. The skin, like breast milk in mammals, contains nutrients necessary for growth.
Now, Blackburn and other researchers have discovered that this behavior may serve another purpose: Much like breast-feeding, it also allows mothers to pass on their unique microbiomes to their babies, which may give their young immune systems a boost. The study, published earlier this year in the journal Animal Microbiome, marks the first known case of amphibians passing microbes from one generation to the next.
Caecilians are a poorly understood group of amphibians that people rarely see in the wild. Many of the approximately 200 species spend almost their entire lives underground or in the shallow streams of tropical and subtropical regions around the world. Like most amphibians, they breathe through their skin, though they can use their lungs to breathe oxygen from the air. These creatures come in a variety of colors and sizes, ranging from a 3.5-inch species in Cameroon to a caecilian that grows nearly five feet long in Colombia.
When researchers discovered the animals’ skin-eating behavior in 2006, they noticed that mothers caring for young grew skin twice as thick as caecilians without offspring. In the week after giving birth, the mothers lost about one-seventh of their weight, which showed up in the stomachs of their young, as Jacqueline Ruttimann wrote for Nature News at the time. Even before birth, some species of caecilians use their specialized teeth to feed on the lining of the mother’s oviduct.
In 2020, researchers discovered oral glands that suggest these creatures may actually have a venomous bite.
“They have a lot of strange features,” Mark Wilkinson, an evolutionary biologist at the Natural History Museum in London, said in a statement after helping describe the 200th caecilian species in 2014. Wilkinson also worked on the 2006 paper describing the skin-eating behavior. “Because they are a poorly known group, the adaptive significance of those features is not well understood.”
But the new study sheds some more light on one of caecilians’ unusual traits. To get a closer look at their microbiomes, the researchers collected skin and gut samples from 14 juveniles, nine adult females and six adult males of an African species called Herpele squalostoma. They also sampled leaves, water and soil in the creature’s rainforest habitat in Cameroon.
After sequencing the bacteria colonies from all samples, the team discovered that very little of what was found in the environment matched the microbiome of the juvenile caecilians. However, each juvenile shared up to 20 percent of their skin and gut bacteria with its mother.
“It’s an example of reproductive ecology having consequences for unrelated aspects of biology,” Wilkinson tells the Times. “They’re kind of lactating in a way.”
First author Marcel Talla Kouete, a researcher at the University of Florida, says in a statement that this study opens up future avenues for research into how microbes benefit the health of these amphibians.
“Is there an evolutionary advantage?” he says in the statement. “If so, are these benefits absent when parental care is circumvented?”