非洲黄冠鼠利用有毒植物抵御捕食者

Woe¹ to the clueless predator² trying to make a meal of the African crested³ rat, a rodent⁴（啮齿类） that applies poisonous plant toxin⁵ to sponge-like hairs on its flanks, a discovery recently made by Jonathan Kingdon and colleagues from the National Museums of Kenya, the Wildlife Conservation Society, and University of Oxford⁶. In the only known instance of a mammal acquiring a lethal⁷ toxin from a plant for defense⁸, the researchers have discovered where the African crested rat (or maned有鬃毛的 rat) gets its poison: the Acokanthera tree, the same source used by East African hunters for poison arrows.

The study appears online in the Proceedings⁹ of The Royal Society B. The authors include: Jonathan Kingdon, Chris Holland, Tom Gheysens, Maxime Boulet-Audet, and Fritz Vollrath of the University of Oxford; Bernard Agwanda of the National Museums of Kenya; and Margaret Kinnaird and Tim O'Brien of the Wildlife Conservation Society.

"The African crested rat is a fascinating example of how a species can evolve a unique set of defenses in response to pressure from predators¹⁰," said Dr. Tim O'Brien, Senior Scientist of the Wildlife Conservation Society and a co-author on the study. "The animal and its acquired toxicity¹¹ is unique among placental mammals."

Scientists have long suspected that the African crested rat is poisonous, primarily due to the animal's specialized¹² behavior, such as exposing a black-and-white coloration（染色） on its flanks when threatened by predators, and accounts of dogs becoming ill or dying after encounters with rats. 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 platypus¹³（鸭嘴兽） and solenodon（沟齿鼠） —the African crested rat finds its toxin (called ouabain) in tree bark.

The researchers confirmed the hypothesis by presenting a wild-caught rat with branches and roots of the Acokanthera tree. The rodent proceeded to gnaw¹⁴（咬） and masticate¹⁵（咀嚼） the bark (avoiding the leaves and fruit) and apply the "slaver" on its flanks. Further, the research team employed electron microscopes to examine the unique structure of the flank hairs. In doing so, they found that the perforated cylindrical¹⁶ structure of the hairs facilitates the rapid absorption of the poisonous saliva¹⁷. Interestingly, ouabain（乌本苷） has also been used by doctors for centuries as a clinical treatment against congestive heart failure.

Besides its warning coloration and poisonous hairs, the African crested rat possesses a thick reinforced skull¹⁸, thick vertebrae（脊椎） , and unusually tough skin, all protection for the small rodent that rarely grows to more than 2 pounds in weight.

Several mysteries about the enigmatic rodent remain, including how the animal uses poison without succumbing¹⁹ to（屈服于） it.