Poison Frogs Losing Their Toxicity, Study Suggests

November 7, 2006

Poison frogs may be losing their toxicity as human development fragments their habitats, a recent study says.

The study examined the diversity of alkaloids found in poison frogs in different regions and habitats on Madagascar, an island nation off the southeast coast of Africa (Madagascar map).

Alkaloids, such as caffeine, nicotine, and cocaine, are bitter-tasting compounds containing nitrogen. In large doses they can be lethal.

The alkaloids poison frogs ingest with their food accumulate in their skin, which makes the animals toxic to would-be predators.

"We looked at only a limited number of sites but found that frog individuals have more different alkaloids at pristine sites and less at fragmented sites," said Valerie C. Clark, a graduate student in chemistry at Cornell University in Ithaca, New York.

While individual alkaloids vary in their toxicity, frogs with a greater variety of the chemicals in their skin are more likely to pack a lethal punch to their predators, Clark notes.

She and colleagues reported the finding last month in the Journal of Chemical Ecology.

The team says future studies need to address the question of whether frogs require a certain number of alkaloids in their skin to maintain their toxicity.

If the answer is yes, some of Madagascar's poison frogs may become defenseless as human development breaks up their habitats, Clark says.

Bug in the System?

According to Clark's study, frogs in pristine forest habitat had about 30 different alkaloids in their skin, whereas frogs in patches of forest surrounded by agricultural fields had only 12 alkaloids.

In a moderately disturbed habitat along the side of a road, the frogs averaged 15 alkaloids.

Continued on Next Page >>




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