Scientists from Utah State University and the Butantan Institute publish evolutionary findings in iScience.
Biologist Edmund ̵
“We consider amphibians – frogs, toads and the like – to be fundamentally harmless,” says Brodie, professor emeritus at the Department of Biology at USU. “We know that a number of amphibians store nasty, toxic secretions in their skin to prevent predators. But learning that you can at least hurt yourself from your mouth is extraordinary. “
Brodie and his colleagues discovered the mouth glands in a family of caecilians, snake-like creatures related to frogs and salamanders. Neither snakes nor worms, caecilians occur in tropical climates in Africa, Asia and America. Some are aquatic and others, such as the Ringelkaecilian (Siphonops annulatus) examined by Brody’s team, live in their own caves.
In 2018, the team reported that the species secreted substances from skin glands at both ends of its snake-like body. The creature concentrates on the head and extends over the entire length of the body. It releases a slime-like lubricant that allows it to quickly dive into the ground to escape predators. At the tail, Caecilian’s glands are armed with a toxin that acts as the last chemical line of defense and blocks a hastily buried tunnel from hungry hunters.
“What we didn’t know is that these caecilians have tiny fluid-filled glands in their upper and lower jaws, with long channels that open at the base of each of their spoon-shaped teeth,” says Brodie.
His research colleague Pedro Luiz Mailho-Fontana, who studied with Brodie as a guest student on the Logan campus of the USU in 2015, noticed the never described mouth glands. With the help of embryonic analysis, Mailho-Fontana, the first author of the paper, discovered that the glands – so-called “tooth glands” – come from a different tissue than the mucous and poison glands in the skin of the caecilians.
“The toxic skin glands form from the epidermis, but these mouth glands develop from the tooth tissues, and this is the same source of development that we find in the reptile poison glands,” he says.
The researchers suspect that caecilians, who have no limbs and only one mouth for hunting, activate their mouth glands when they bite on prey such as worms, termites, frogs and lizards.
The team does not yet know the biochemical composition of the liquid contained in the mouth glands.
“If we can demonstrate that the secretions are toxic, these glands could indicate an early evolutionary design of the oral venom organs,” says Brodie. “They may have developed earlier in caecilians than in snakes.”
For more information on this discovery, see Snake-like venom glands discovered along the teeth of amphibians.
Reference: “Morphological Evidence for an Oral Poison System in Caecilian Amphibians” by Pedro Luiz Mailho-Fontana, Marta Maria Antoniazzi, Cesar Alexandre, Daniel Carvalho Pimenta, Juliana Mozer Sciani, Edmund D. Brodie Jr. and Carlos Jared, July 3 2020, iScience.
DOI: 10.1016 / j.isci.2020.101234