Snake-like venom glands found in amphibians for the first time

Hyperaxion Jul 3, 2020

Researchers have found that caecilians have a venomous bite, similar to snakes.

A group led by researchers from the Butantan Institute, Brazil, described for the first time the presence of venom glands in the mouth of an amphibian. The legless animal that lives in an underground environment, known as caecilian, has glands connected to the teeth that, when compressed during the bite, release a secretion that penetrates the wound.

Snake-like venom glands found in amphibians for the first time
(Credit: Carlos Jared).

This animal feeds on earthworms, insect larvae, small amphibians and snakes, and even small rodents. The study was published in the open access journal iScience.

“It is while examining the mucous glands of the ringed caecilian that I stumbled upon a never before described set of glands closer to the teeth. The poisonous skin glands of the ringed caecilian form from the epidermis, but these oral glands develop from the dental tissue, and this is the same developmental origin we find in the venom glands of reptiles,” said Pedro Luiz Mailho-Fontana, first author of the study.

In an article published in 2018 in Scientific Reports, the team demonstrated that in addition to mucus glands scattered over the body’s skin, caecilians have a high concentration of poison glands in the skin of the tail, as a means of defense against predators. This characteristic, which also exists in frogs, tree frogs, and salamanders, poisons the predator when it bites the animal.

The same group was also the first to demonstrate, in a study published in the journal Nature in 2006, that caecilians of the species Boulengerula taitanus feed exclusively on the mother’s skin in the first two months of life. In 2008, the group described the same behavior in the species Siphonops annulatus, in an article published in Biology Letters.

Now, the researchers have shown that caecilians can be venomous, and that they would be the first amphibians to have an active defense mechanism, when the venom is used to attack, as do snakes, scorpions, and spiders. The secretion that comes out of the glands also serves to lubricate the prey and facilitate its swallowing.

(Credit: Carlos Jared).

Except for a group that lives in aquatic environments, caecilians spend their entire lives in underground tunnels. For this reason, they have reduced eyes that perceive light, but do not form images. They are also the only vertebrates that have tentacles, close to the eyes, that recognize the environment by touch and chemical receptors.

Venom

Biochemical analyzes have shown that the secretion that comes out of the animal’s mouth during the bite contains phospholipase A2, an enzyme quite common in the venom of animals such as bees, wasps, and snakes. The activity of this enzyme was higher than in the rattlesnake venom. It is not possible to state by this characteristic, however, if the animal is more or less venomous than the snake.

The group will now carry out new tests using molecular biology techniques to more accurately examine the secretion and confirm its venomous character. In the future, the enzyme could be tested for biotechnological uses, such as the development of pharmaceutical drugs.

In the study, four species of caecilians were analyzed. In one of them, Typhlonectes compressicauda – the only one that lives in an aquatic environment – the glands were found only in the animal’s mandible, the lower part of the mouth, and not in the maxilla, the upper part.

The researchers believe that, just as it happened in the evolutionary process of some aquatic snakes, this group of caecilians lost such structures, since the water naturally lubricates the prey. The species maintained, however, the mandibular glands, probably with venom.

With most of the 214 known species living underground in the rainforest regions of South America, India, and Africa, caecilians are some of the animals that science least knows about. More than new data about the animal, this new study brings important information about the evolution of amphibians and reptiles.

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