for National Geographic News
For ten years a facial cancer has threatened to wipe out Australia's Tasmanian devils. (See "Tasmanian Devils Decimated by Mystery Cancer.")
The cancer is spreading fast, and scientists now say the disease transferred in tooth-baring combat.
Pound for pound, the Tasmanian devil is reportedly the most powerful biter alive today. Once widespread in Australia, the 20-pound (9-kilogram) marsupials now live only on the Australian island of Tasmania (map).
With as many as 150,000 roaming the wilds, the devils long seemed safe from extinction. Then in 1996 a nature photographer took a picture of a Tasmanian devil with a grotesque facial tumor.
Now dubbed devil facial-tumor disease, the ailment produces enormous growths that push the animals' teeth out of line and make it difficult for them to eat. Afflicted animals generally die of starvation within six months.
The disease has spread rapidly. Today biologists report that few animals evade it long enough to live into old age, which for a Tasmanian devil means about five years.
Scientists have long known the disease is infectious, but nobody understood what caused it. Some suspected that it might be transmitted via a virus.
But Anne-Maree Pearse, a biologist at Tasmania's Department of Primary Industries, Water, and Environment, thought something more exotic might be at work.
Now she and coworker Kate Swift believe they've found the answer: The animals inject cancer cells into each other when they engage in mating battles.
It's a unique theory, because veterinarians know of only one other type of cancer that can be transmitted by physical contacta venereal disease that affects dogs.
During mating season, Tasmanian devils are notoriously feisty, and their duels often involve mouth-to-mouth combat.
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