Frogs with a Toxic Taste.

• Author: Hardman, Chris

SCIENTISTS HAVE long wondered how poison frogs become poisonous. Are they born with the poison or do they manufacture it as adults? Research by University of Oklahoma professor Janalee P. Caldwell links the source of toxin in Amazonian poison frogs to their diet. They eat lots of ants, and the less toxic species of frogs eat fewer ants.

Caldwell is an expert in poison frog diets, with research projects sponsored by the National Science Foundation and the National Geographic Society. In one of her recent studies, she analyzed the diets of nine species of toxic and nontoxic frogs in the poison frog family from Nicaragua and Ecuador. Caldwell found that the poisonous flogs had diets composed of 50 to 73 percent ants, while the nontoxic flogs had a much more diverse diet, feasting mostly on a variety of flies, with ants making up only 12 to 16 percent of their diet. Ants are known to have toxins, called alkaloids, so Caldwell speculates that they are the source of poison. "It looks like ants are the most common thing in the diet so it's a correlational [theory] at this point," she says.

Originally scientists believed that poison flogs manufactured their own poison. Studies by National Institutes of Health chemist John Daly showed that captive frogs, who were deprived of their normal diets, didn't develop poison. When the captive frogs were fed ants or fruit flies dusted with an alkaloid, the flogs developed some toxins in their skin. Caldwell expanded on that research by determining exactly what poisonous and nonpoisonous frogs eat in the wild.

Another characteristic that sets these frogs apart is their bright coloring. These half-inch to two-inch amphibians come in vibrant...