You don’t need udders to nurse your little ones! Contrary to what has long been thought, “breastfeeding” is not the prerogative of mammals. Some spiders do it too. The latest animals to surprise scientists are cecians, a diverse group of worm-like amphibians (also called gymnophiones, or legless amphibians) that closely resemble snakes. And more specifically the female of this species Siphonops annulatusoriginally from Brazil, who feed their newborns with a liquid they secrete themselves.
In any case, an international team of researchers just proved it in a study published on March 7, 2024 in the journal Science, to everyone’s surprise. Their work expands our understanding of parental care and communication in cetaceans.
A substance similar to the milk of mammals
Most of these animals spend most of their time underground, which explains why “Caecilians are probably the least known of the vertebrate groups“, explains Science and the future Carlos Jared, an evolutionary biologist at the Butantan Institute in São Paulo (Brazil) and co-author of the study. Some species have adapted so well to life underground that they have completely lost their eyes.
Since 1987, his team has been interested in milk production in caecilians. After several trips to the cacao plantations of the Brazilian Atlantic Forest, scientists managed to collect 16 females of the cecilia species. Siphonops annulatus and their many young. Each mother has four to thirteen children. Back in the lab, they filmed each family for two months after hatching, until the wormy amphibians became independent.
They then discovered that not only did each mother never leave her litter, even to feed, but that she also produced a lipid- and carbohydrate-rich substance – similar to mammalian milk – from her cloaca (a duct-like organ found in birds, reptiles). , amphibians), which the young absorb through enlarged glands along the mother’s oviduct.
Strengthening the immune system of newborns
This process appears to be triggered by physical contact and sound signals emitted by the offspring, a form of communication previously unheard of among amphibians. “They cry and make “click click click click” sounds as if demanding,” says Pedro Luiz Mailho-Fontana, a postdoctoral researcher at the Laboratory of Structural Biology at the Butantan Institute in São Paulo and lead author of the study that reviewed the video lessons.
Young babies suck this “milk” several times a day and can grow to more than double their size in the first week alone. Provisioning continues for about two months after hatching, which promotes rapid growth of the young Siphonops annulatus. According to the researchers, breastfeeding could support the microbiome and immune system of these newborns, as it does in humans.
“Here we observe a combination of the hatching of the egg and the development of the young, which live freely and feed on the mother’s secretion… It is impressive“, he exclaims Science and the future Annemarie Ohler, a zoologist and herpetologist at the National Museum of Natural History in Paris, who was not involved in the study.
Female Siphonops annulatus with her eggs. Credits: Carlos Jared
An evolutionary step?
For Pedro Luiz Mailho-Fontana, given that not all of the hundreds of caecilian species lay eggs, this strange combination of egg-laying and milk secretion would be an evolutionary step that allows us to move from one laying method to another. “It is absolutely uniquethe researcher continues. Evolution happens in many different non-linear ways!’
Marvalee Wake, a professor of integrative biology at the University of California, Berkeley (United States), who was not involved in the study, believes that female caecilians may simply be caring mothers who use different feeding techniques.
However, these results are only a starting point: “We still don’t know if other caecilian species behave this way! We also don’t know how, why, when, or even where this amphibian milk came from during evolution.details of Science and the future biology teacher. “Gymnophiones have enormous morphological limitations because they are burrowers and live in the ground. In fact, there is very little data on their behavior. So I think we can expect more surprises!” adds Annemarie Ohler.
One thing is certain, however: this discovery opens up new perspectives on the evolution of reproductive strategies and sheds valuable light on evolutionary biology.