These worm-like amphibians may have venomous saliva

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These worm-like amphibians may have venomous saliva

Venom is nearly unheard of in amphibians, making the mostly blind, legless creatures called caecilians extremely unusual.

 

The Mexican caecilian (above, an individual kept at the St. Louis Zoo in Missouri) is one of 200 known species of the subterranean amphibians.

 

Photograph by Joel Sartore, National Geographic Photo Ark

 

Toothy worm-like creatures called caecilians have smooth, shiny skin and already look a lot like snakes. Still, scientists were surprised to discover some of these legless animals

 

may have venomous saliva—possibly the first example ever found in amphibians.

 

Nearly 200 caecilian species wiggle through tropical forests the world over, ranging from the 3.5-inch-long Idiocranium russell in Cameroon to the nearly five-foot-long giant

 

known as Caecilia thompsoni in Colombia.

 

Most of the animals dwell underground, which is why “caecilians are maybe the most unknown group of vertebrates,” says Carlos Jared, an evolutionary biologist at the Butantan

 

Institute in São Paulo, Brazil, and author of a new study on the animals. Some species are so adapted to subterranean life, they’ve completely lost their eyes.

 

Scientists already knew caecilians have three rows of needle-nosed teeth—two on the top and one on the bottom—that likely help the predators catch and gulp down

 

earthworms. But while looking at caecilians captured in Brazil, Jared discovered a never-before-described set of dental glands that produce saliva and, possibly, venomous

 

enzymes. But, he cautions, further analysis is needed to confirm caecilian saliva is truly venomous.

If it is, the implications are striking, says Emma Sherratt, an evolutionary biologist at University of Adelaide in Australia who was not part of the study.

 

For one, it would mean that venom evolved independently in both amphibians and reptiles, which would reconfigure what we know about how venom evolved. It also presents

 

an intriguing mystery, she says: Why don’t frogs and salamanders also have venomous saliva? (Learn more about the origin of venom.)

 

 

 

A museum specimen of a giant caecilian (Caecilia pachynema) reveals its three rows of teeth.

 

Photograph by Alejandro Arteaga

 

Toothy worm-like creatures called caecilians have smooth, shiny skin and already look a lot like snakes. Still, scientists were surprised to discover some of these legless animals

 

may have venomous saliva—possibly the first example ever found in amphibians.

 

Nearly 200 caecilian species wiggle through tropical forests the world over, ranging from the 3.5-inch-long Idiocranium russell in Cameroon to the nearly five-foot-long giant

 

known as Caecilia thompsoni in Colombia.

 

Most of the animals dwell underground, which is why “caecilians are maybe the most unknown group of vertebrates,” says Carlos Jared, an evolutionary biologist at the Butantan

 

Institute in São Paulo, Brazil, and author of a new study on the animals. Some species are so adapted to subterranean life, they’ve completely lost their eyes.

 

Scientists already knew caecilians have three rows of needle-nosed teeth—two on the top and one on the bottom—that likely help the predators catch and gulp down

 

earthworms. But while looking at caecilians captured in Brazil, Jared discovered a never-before-described set of dental glands that produce saliva and, possibly, venomous

 

enzymes. But, he cautions, further analysis is needed to confirm caecilian saliva is truly venomous.

 

If it is, the implications are striking, says Emma Sherratt, an evolutionary biologist at University of Adelaide in Australia who was not part of the study.

 

For one, it would mean that venom evolved independently in both amphibians and reptiles, which would reconfigure what we know about how venom evolved. It also presents

 

an intriguing mystery, she says: Why don’t frogs and salamanders also have venomous saliva? (Learn more about the origin of venom.)

 

 

 

He agrees with the authors that, if it’s there, the venom likely adapted to help caecilians take down or dissolve prey, not defend against predators, he says.

‘Constantly surprising us’

Kevin Arbuckle, an evolutionary toxinologist at Swansea University in the United Kingdom, says it’s “certainly plausible” that caecilians are venomous, given how understudied the

 

animals are.

 

But the analysis of the enzymes isn’t “particularly convincing,” Arbuckle said in an email. “All oral glands produce a wide range of enzymes, including many of those listed.” In

 

other words, animals can have this family of enzymes in their saliva without having a venomous variety.

 

“That said, it's clearly an interesting paper and I have no doubt it will spurn many follow-up studies that will greatly improve our understanding of a poorly known group of

 

vertebrates,” he says.

 

Sherratt adds that while the paper is a “solid contribution,” it “leaves us with a lot more questions than it answers.”

 

“But then, that’s the case in caecilians,” says Sherratt. “They’re constantly surprising us.”

 

 

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