August 3, 2011

African Rat Uses Plant Poison To Ward Off Enemies

Researchers studying the African Crested Rat have found that it uses an ingenious tool to ward off predators. The rodent consumes a poisonous plant toxin and spits the saliva onto sponge-like hairs on its fur.

Jonathan Kingdon and colleagues from the National Museums of Kenya, the Wildlife Conservation Society, and University of Oxford published their observations of this study online in the Proceedings of The Royal Society B.

When attacked by predators, the rat puts on a dramatic fur-bristling display and if an animal gets a mouthful of the hair, the predator lives to regret it, or dies from heart failure. Dogs have been known to collapse and die rapidly after biting a Crested Rat. Others that have survived an encounter shy away from the creature, according to local reports.

"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 Dr. Tim O'Brien, Senior Scientist of the Wildlife Conservation Society and a co-author on the study. "The animal and its acquired toxicity is unique among placental mammals."

Scientists have long suspected that this animal was poisonous, primarily due to the rat's specialized behavior, of exposing a black-and-white coloration on its flanks when threatened by predators.

The new discovery concerns the nature of the chemical defense. Instead of producing poison itself "” as is the case with poisonous mammals such as the duck-billed platypus and solenodon "” the African crested rat finds its toxin (called ouabain) in tree bark. Bushmen in Kenya use the same poison to tip arrows which can fell an elephant.

The researchers were surprised by what they discovered when they examined the animal's poison hairs in the laboratory. Professor Fritz Vollrath, another member of the Oxford University team, told the Daily Mail: "None of us had ever seen complex hair such as these with a latticework for the wall and a bundle of fine fibers for the core."

"It was surprising how effectively the hair was in "wicking-up" liquids, and then holding them fast. While the function of a reservoir for the poison was clear, we shied away from testing it by chewing a hair."

The Crested Rat appears to be completely immune to ouabain, which is well known for its heart-arresting properties.


Image Caption: The African crested rat is the only mammal known that acquires its poison from a plant. The rodent masticates the poisonous bark of the Acokanthera tree and applies the mixture to its flank hairs, which absorb the poison like candle wicks. Credit: Susan Rouse


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