Australian Frog—First Vertebrate to Make Poison

Laura Lewis
for National Geographic News
May 17, 2002

Scientists have discovered a wild Australian frog stocked with its own ammo and prepared for chemical warfare.

The frog, of the genus Pseudophryne, secretes a unique poisonous alkaloid from its skin, which offers protection from would-be predators.

This poisonous system of defense is not in itself surprising. Researchers have shown that certain frogs secrete the poisons that they obtain by eating a diet high in such poisons, which belong to a class of compounds known as alkaloids. But the new study represents the first documented case of a vertebrate producing its own alkaloids—essentially manufacturing the poisons on its own.

"You may think after 30 years of looking at frog skins for alkaloids there wouldn't be any surprises left," says John W. Daly, a biochemist with the National Institutes of Health in Bethesda, Maryland, who led the research. But the discovery of the self-initiated poison production, he said, "was completely unexpected."

The finding was reported in April in the Journal of Natural Products.

During many years of research, Daly and his team previously discovered that certain frogs from tropical forests all over the world have skin alkaloids.

Alkaloids are complex organic compounds of nitrogen, usually from plants, that can be very poisonous. Their various forms include such drugs as cocaine, quinine, strychnine, morphine, and nicotine.

The unique alkaloids of frog skin protect the amphibians from predators and perhaps from skin infections by microbes and fungi. Snakes, for example, often prey on frogs but spit them out upon tasting the poison.

Jerrold Meinwald, the Goldwin Smith Professor of Chemistry at Cornell University in Ithaca, New York, said he was pleased to learn that frogs have evolved the ability to manufacture inborn chemical defense. "I would have been surprised if there weren't frogs to do the necessary chemistry that insects do all the time. It makes perfectly good sense," he said.

Eventual Medical Impacts?

Daly and his colleagues first learned that Pseudophryne had unique alkaloids in its skin when they were studying the frog in the late 1980s. The researchers named the new class of alkaloids "pseudophrynamines," after the frog's genus.

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