poison dart frogWhen Shakespeare’s witches stirred their stew of “Eye of newt, and toe of frog,” in the fourth act of Macbeth, they were using folk knowledge nearly as old and widespread as humankind: Amphibians are strong medicine.

European traditions attributed everything from warts to witchcraft to toads and their kin. By contrast, the Choco Indians of Colombia recognized the toxic properties of the brightly colored little frogs hopping around the rainforest floor and used them to make poison blowdarts for hunting. Other South American Indians knew that some species of frogs had healing properties in their skin secretions and rubbed the animals across wounds.

Modern medicine has caught up, and scientists in the United States and elsewhere have discovered that the toxic skin secretions of a variety of frog and toad species contain hundreds of chemical compounds that are a veritable pharmacopoeia of wonder drugs, from potent painkillers to potential treatments for the most deadly cancers.

It’s in the skin
All frogs and toads have two types of glands in their skin. The mucous glands, which occur all over the body, continuously secrete a clear, viscous—or slimy—coating that keeps the animal moist and enables it to absorb both water and oxygen through its permeable skin.

The granular, or poison, glands are distributed across the body, often with the heaviest concentration around the head and neck, where a frog or toad is most likely to be grabbed by a predator.

The granular glands are among frogs’ and toads’ most important defense mechanisms, along with escape and camouflage. When activated by stress or injury, the glands secrete a milky substance that varies by species from slightly noxious to drop-dead toxic. The poison for which the dart frogs you’ll see in Amazon Rising are so well known falls into the latter category. Ironically, some of these powerful dendrobatid toxins—from frogs in about a dozen genera including Dendrobates, Oophaga, Epipedobates and Phyllobates—offer the most pharmaceutical promise.

Dendrobatid toxins contain alkaloids, which are complex, often bitter compounds that act on the nervous system. Most alkaloids, including caffeine, nicotine, quinine, cocaine, morphine and curare, are derived from plants. And plants appear to be the source of these little frogs’ poison, in a roundabout way. Scientists believe the alkaloids are present in the frogs’ plant-eating prey—assorted insects—and that the chemicals are assimilated by the frogs and stored in the granular glands.

Epibatidine is an alkaloid exclusive to phantasmal dart frogs, the common name for two closely related species, Epipedobates anthonyi and E. tricolor. The frogs’ bright coloration—ranging from cherry red to burgundy, with solid or broken stripes of citron green to bright yellow—is a dead giveaway that they are toxic. Epibatidine is chemically similar to nicotine. (That familiar plant compound is toxic when ingested or absorbed through the skin.)

A small amount of epibatidine from one of these inch-long frogs can drop a would-be predator many times its size by triggering a rapid cascade of skyrocketing blood pressure, respiratory paralysis, seizures and death. But research has also shown that epibatidine has amazing painkilling properties, 200 times more potent than morphine, yet without any addictive side effects. Unfortunately, lab tests with mice demonstrated that there is too fine a line between a medicinal dose and a lethal one. A synthetic version of epibatidine may hold more promise.

All of Shedd’s dart frogs, including the phantasmal (we have E. anthonyi), enjoy healthy, but alkaloid-free diets, so their potential for poisoning anyone is pretty low. You can find phantasmal dart frogs in a focus habitat at the foot of the stilt-leg house in the Low-Water Season section of Amazon Rising.

In the wild, they live in moist lowlands and dry forests up to 5,800 feet in southwestern Ecuador’s Andes. The female lays her eggs in leaf litter, and the male carries the larvae to nearby streams to develop. Clean water, therefore, is as essential to the species’ survival as is forest habitat. Both are disappearing, and E. anthonyi has been classified as near-threatened by the International Union for the Conservation of Nature (IUCN). The frogs are most threatened by habitat loss, as forests are cleared for small farms, and, ironically, by poisoning from pesticides, fertilizers and other chemicals that are polluting their streams. And a cure for that has yet to be found.

Posted by Karen Furnweger, web editor