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Skin as food

Offspring of the caecilian amphibians feed on the secretion and skin of their mother

Normally they are slimy and considered a little repugnant, but there is no way of denying that they are self-denying mothers, even when one cannot see their young. At least two species of caecilian amphibians – the Siphonops annulatus, found in Brazil, and the Boulengerula taitanus, from Kenya – let their offspring nibble at the most superficial layers of their skin, which contains a secretion rich in fats and proteins, during the four or five weeks in which they dedicate themselves to maternal care. The skin, dark gray before reproduction, then turns light gray and is replaced while the heirs devour it. When they are near, probably the venom glands, which are spread over the entire elongated body surface of the mother, stop working.

This manner of looking after offspring doesn’t just call the attention because of its exotic nature: it is also important from the evolutionary point of view. According to Carlos Jared, a biologist from the Butantan Institute, this behavior of the worm-lizard  who lay eggs emerged at least 150 million years ago, when South America and Africa had formed a single continental block, and perhaps was  right at the start of the evolution of this group of animals that began to evolve around 250 million years ago. Only much later is it that the species of egg-laying caecilian amphibians appeared, whose eggs develop within the mother’s body – and the young are born looking like small adults. Before they are born, the offspring feed themselves by scratching the walls of the uterus with their pointed teeth, which then liberates a nutritive juice. “To eat the mother’s uterus would be a derived form of behavior”, he says.

However, one is not speaking of an artifice exclusive to amphibians, the animal class to which the caecilian amphibians belong. Even today one can note a similarity in the duck billed platypus (Ornithorhynchus anatinus), possibly the strangest of the mammals, with a flat beak like that of a duck, a body covered with hair and four flippers, which lives in the rivers and lakes of Australia. The offspring of the duck billed platypus are born from eggs and lick the maternal milk secreted through the pores of the female’s stomach skin, as she does not have nipples, different from other mammals. “We note in these African and Brazilian caecilian amphibians very interesting aggregation behavior, since the mothers remain coiled up around their young whilst they care for them”, comments Marta Antoniazzi, a biologist from the Butantan Institute. A very simple test suggested that the secretion liberated by the skin, as well as serving as food, can contain pheromones capable of attracting the young. The researchers separated the mother and young, very like pink garden worms, and observed: in a few seconds they began to move in her direction, even though they are completely blind.

In the South of the state of Bahia
The caecilian have only primitive eyes, also known as vestigial organs. The eyes are positioned over the skin and can only distinguish light and dark, which is enough to indicate if it is day or night and if it is possible to leave the safety of the subterranean tunnels in which the animals live. Gifted as well with sensitive tentacles, small prominences with which they probe their way forward, the close to 180 species of caecilian known worldwide, represent the gymnophiona order, one of the three orders of amphibians, alongside the anura (frogs, toads and tree toads) and the salamanders. They resemble snakes or long worms, but one wouldn’t be wrong to see them as elongated frogs without hind legs that live, mate and look after their young in borrows and dug out chambers underground. At times they can also be found alone, or with their young, in other dark environments such as a tree stump or a rotted cacao tree in the forest, in the middle of insects and worms, their preferred food.

It was in one of these piles of rotted trunks, during another expedition in 1993 into the Atlantic Rainforest between the towns of Ilheus and Itabuna, in the south of the state of  Bahia, that the group led by Jared and Marta found the species Siphonops annulatus with skin lighter in color than normal. A scientific investigation then began that ended on the 13th of last month, when an article in which they describe for the first time the maternal caring of the African species, adopted as the study model because they are better known than the Brazilian, in the scientific magazine Nature. The Siphonops can reach 40 centimeters in length, whilst the Boulengerula taitanus can reach half of that and is thinner.

Intrigued with the color change of the Brazilian species, Jared commented on his findings with Mark Wilkinson, a specialist on amphibians, from the Natural History Museum of London, with whom he had already worked.  Wilkinson also found it intriguing and wrote to Ronald Nussbaum, a specialist on the gymnophiona order who works at Michigan University, in the United States. Nussbaum, who knew that in some caecilians the offspring scratched their mother’s uterus, proposed to his colleagues that the oviparous caecilians could show similar behavior, as the offspring fed on the mother’s skin.

Once the hypothesis was established, the biologists began to work in order to classify what seemed to be a type of maternal behavior that had not then been described. The description of this mechanism, including the transformations on the skin and the identification of the preliminary composition of the secretion, which had to be highly nutritious, since the offspring grew at around 1 millimeter per day, also mobilized Hartmut Greven, from the University of Düsseldorf, Germany, and another two biologists from the Natural History Museum of London, Alexander Kupfer and Hendrik Muller, also linked to the University of Leiden, in Holland. They have already arranged to return to the humid forest in the south of Bahia at the end of this year to collect samples of the secretion and to observe the behavior of the Brazilian caecilian amphibians right from the birth of the young.