devil destroyer. cancerous tumors decimating Tasmanian devil populations.
Menna Jones
Contagious cancer was sweeping the populations of Tasmanian devils, killing most adults. Now, young devils spawn earlier than ever before. But is this a case of rapid change or just a temporary response to a changing environment?
Tasmanian devil facial tumor disease resurfaced in Tasmania there about 10 years and now affects the majority of devils on the island ( science , 18 February 05, p. 1035). Lesions around the animal's mouth can reach a size of ping-pong balls and spread on the face; unable to eat, demons are starving in the months of the onset of cancer. The disease is highly contagious, and adults are particularly vulnerable, perhaps because the tumor cells are often spread during sexual contact. The problem was so devastating that the Tasmanian devils were declared a threatened species in May.
zoologist Menna Jones of the University of Tasmania has also noticed a surge in pregnancies 1 year devils. Normally, the animals, which live about 6 years do not occur before age 2. But when Jones and his colleagues gauged the age and reproductive status of demons - via tooth erosion and organ development sex - they have found evidence for the breeding of several months to a year earlier than normal at the four sites of the five studied. The proportion of first breeding females has reached an astonishing 83% in one place, the team reports this week in the Proceedings of the National Academy of Sciences .
The transition to early farming could be an evolutionary response, Jones said. By killing adults that breed after two years, the cancer could be genetic selection for younger breeding females, she notes. If so, the results would make the devil the first mammal known to rapidly evolve their reproductive modes in response to a disease.
Evolutionary biologist Nelson Hairston Cornell University is skeptical. Young devils may have started breeding early simply because they have better access to food and mates, now that fewer adults are on the scene. To really make the case for genetic evolution, he said, the team should demonstrate that the devils from zoos, for example, would not adopt early reproduction in response to more food and mates.
Hairston also note that scientists have shown the rapid evolution of mammals such as rabbits and sheep, but not in response to the disease ( science , 16 March 07, p . 1571). Thus, the history of Tasmania would not cause a change in our understanding of evolution. "But it would add a sexy example [of the phenomenon]," he said.
With reporting by Lauren Cahoon.
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