East African hunters who shoot poison-dipped arrows are not the only ones using the Acokanthera tree for its toxin. A small, black-and-white rat also slathers the poison, called ouabain, on its fur to keep predators at bay.

The African crested rat is the first known mammal species to protect itself this way, a fact recently confirmed by a team of scientists that included WCS鈥檚 Tim O鈥橞rien. Dogs have been known to fall ill or die after eating the rat but no one knew exactly why. In , the researchers discovered the answer.

They observed the rat chewing the tree鈥檚 bark to concoct a frothy mix of saliva and ouabain, which it then spread along the sides of its body. The two-pound animal鈥檚 skull and vertebrae are thick and its skin is unusually tough. But the key survival feature of the rodent, also called the maned rat, is its fur.

The animal鈥檚 distinct white-and-black coloration sends a 鈥渄on鈥檛 eat me鈥� signal to predators, and when threatened, the rat typically displays its markings as a warning. And that鈥檚 not all. Examining the fur under an electron microscope, the scientists saw that the cylindrical hairs are perforated. This structure helps them rapidly absorb the rodent鈥檚 deadly sputum, making for a more potent protection.

听鈥淭he African crested rat is a fascinating example of how a species can evolve a unique set of defenses in response to pressure from predators,鈥� said Dr. O鈥橞rien, a WCS senior scientist. 鈥淭he animal and its acquired toxicity are unique among placental mammals.鈥�

Other poisonous mammals do exist, for example, the solenodon and the egg-laying duck-billed platypus. Those animals, however, produce their toxins themselves with no need for a toxic tree. While the African crested rat avoids nibbling on the Acokanthera tree鈥檚 leaves and fruit, just how the rodent keeps from sickening itself remains a mystery.


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