Australia's Tasmanian devils are breeding at younger ages in response to a strange form of infectious cancer that is spreading rapidly through devil populations. The feisty marsupials are now reproducing before the lethal cancer strikes them down—a response that may be the species' only chance to avoid extinction. Researcher Shelly Lachish explains:
"In a normal, healthy devil population the females would rarely breed before the age of two, but now 60 per cent of one-year-olds in diseased populations have produced young.... They are teenagers in human terms. It's a remarkable change given early breeding was once very, very rare" [Sydney Morning Herald].
The cancer was first detected in 1996, and since then it has halved Australia's population of wild devils.
While some researchers believe this to be an example of rapid evolution, skeptics say the case is not yet closed.
This disease spreads through biting, which appears to be a common form of social interaction among the devils, especially during mating season [Ars Technica]. Cancer cells are deposited on an infected devil's face, where they grow into grotesque facial tumors that eventually prevent the creature from eating.
Researchers say the early sex adaptation may not be enough to save the feisty marsupial species; the disease
could lead to the marsupial carnivore's extinction within 20 to 25 years [AFP].
The rapid behavioral change looks like natural selection in fast-forward, says researcher Menna Jones:
"The devils are under intense selection for early breeding because the disease is 100 per cent fatal. Any devil that's successful in breeding more than once is putting out more of its genes into the pool of survivors" [Telegraph].
In a report published in the Proceedings of the National Academy of Sciences [subscription required], researchers say their studies of devil populations at five sites illustrated this theory.
But evolutionary biologist Nelson Hairston says the researchers haven't done enough research to convince him that the devils are evolving genetically, and aren't just responding to a changed environment. The 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 truly make the case for genetic evolution, he says, the team would have to show that devils taken from zoos, for example, would not adopt early breeding in response to more food and more mates [ScienceNOW Daily News].