African rat protects itself with poison

Researchers, including U.S. conservationists, say they've discovered the first known mammal to use plant poison to defend itself. A predator trying to make a meal of the African crested rat is in for a surprise, the researchers said, because the rats apply a poisonous plant toxin to sponge-like hairs on its flanks. The "African crested rat is a fascinating example of how a species can evolve a unique set of defenses in response to pressure from predators,"" said study co-author Tim O'Brien of the Wildlife Conservation Society in a WCS release Tuesday. The "animal and its acquired toxicity is unique among placental mammals." The researchers discovered the rat gets its poison from the bark of the Acokanthera tree, the same source used by East African hunters for poison arrows, by chewing the bark and applying its saliva to its flanks. Scientists have long suspected the African crested rat is poisonous, with many accounts of dogs becoming ill or dying after encounters with the rodents. But instead of producing poison itself, as the duck-billed platypus does, the African crested rat takes its toxin, called ouabain, from the external source, the tree. A remaining mystery, researchers say, is how the animal uses the poison without succumbing to it.