NY Science Times

September 2, 2003

OBSERVATORY
Frogs as a Poison Factory
By HENRY FOUNTAIN

Many tropical frogs employ chemical weapons as protection, toxic compounds in the skin that can cause convulsions or other unpleasantness in those predators unfortunate enough to touch or taste them.

But such poisonous frogs have always been thought to be more weapons storehouses than factories, not synthesizing the toxic alkaloids but accumulating them from the insects they eat.

Now, however, scientists from the National Institutes of Health and the National Aquarium in Baltimore have discovered that certain poisonous frogs have a bit of the chemist in them. These frogs, of the genus Dendrobates, take a poison obtained from the diet and make it stronger.

The scientists made the discovery accidentally, while trying to study how efficiently the frogs accumulated alkaloids from different sources. They studied one class of alkaloids, known as DHQ, which the frogs obtain from ants, and another, PTX, that comes from unknown insects.

The researchers fed the frogs a synthetic DHQ and a synthetic PTX. When they analyzed the toxic compounds in the frogs' skin, they found that four-fifths of the PTX had been converted to a much more potent form that caused convulsions and death in mice at one-fifth the dose of the original. The findings were reported in The Proceedings of the National Academy of Sciences.

The researchers conducted similar experiments with poison frogs of other genuses and uncovered no modified PTX. The results, they say, suggest that although many frogs accumulate toxins unchanged, those of the genus Dendrobates have uniquely evolved an enzyme that can modify one of them.