Evolution at warp speed

Sydney - Imagine the mayhem if cancer were contagious.

That is the lot of the Tasmanian devil, a cat-sized animal being pushed to extinction by lethal tumours passed on in fights over food or sex.

In the 15 years since the first cancer case, the population of the world's largest carnivorous marsupial is down by 85 percent.

There may be fewer than 20,000 cancer-free individuals left on the Australian island of Tasmania, its last refuge.

“This is a very unusual disease in that it's 100-percent lethal,” said Rodrigo Hamede, a zoologist at the University of Tasmania in Hobart. “We hope the devils will learn to deal with it in the same way that canines did with dog cancer.”

It is a slim hope. What usually happens in evolution is a nasty form of self-preservation in which diseases become less virulent and victims better able to survive them.

That is what happened with canine transmissible venereal tumour. Lethal thousands of years ago, dogs' immune systems learned to detect it and deal with it. After one bout, they are immune for life.

For the devils to recognise a threat and throw up their defences, evolution will have to move at warp speed.

Some give the wild population just another 20 years.

“Things are occurring at a very fast rate so I expect the evolutionary steps required to achieve coexistence are going to be accelerated as well because of the massive mortality of this disease,” Hamede said.

“There's no interest in the disease running out of hosts because it would drive itself to extinction.”

Things must be very bad for scientists to lay faith in evolution. And they are.

“Hopes of the disease petering out are gone,” said Sydney University veterinarian Kathy Belov. “We know that this cell line is immortal and will continue to grow and divide and pass from animal to animal.”

Captive breeding in Tasmania has begun and is going well. Sanctuaries for disease-free devils have been set up in mainland Australia. The latest initiative is to release healthy devils to roam free on tiny Maria Island, off Tasmania.

Scientists are determined to avoid the fate of the Tasmanian tiger, another carnivorous marsupial that became extinct in the 1930s. The last tiger, or thylacine, died in Hobart Zoo in 1936.

Hamede said the evolution is evident. His research shows that the least aggressive individuals live the longest. The more biting they do, the quicker they pick up the infection.

“Natural selection is doing its bit,” he said. “Those animals that are exhibiting behaviour that makes them less likely to acquire infection are the ones who are going to survive for longer and pass on their genes.”

It is a desperate remedy, but getting rid of the most aggressive animals and favouring the mild-mannered, more resilient ones might enhance the overall chances of survival.

There is no vaccine or treatment for the cancer. It is not a virus or a bacterium, but an actual cancer cell that is passed from animal to animal.

“It's surprising because normally you can't catch cancer,” Belov said. “There are some cancers that are caused by viruses, like cervical cancer caused by papilloma virus, but there the virus makes you at risk of catching cancer. In devils, it's the cancer cell that's the infectious agent.”

As the numbers go down, so do the chances of survival. As well as disease, there are other threats. Habitat is being lost and there are more competitors and more predators.

Belov said that accelerated evolution, with the devils getting to cope the way dogs did, would be marvellous.

“It would be brilliant if (it) went the same way, but we may not have enough animals left to allow that to happen. Dogs, after all, are much more widespread ... but devils are now found only in Tasmania.”

Hamede agreed that time was running out and salvation would not come through a scientific breakthrough.

“We can't eradicate this; it's completely unrealistic,” he said.

“What we need to do is manage the disease itself, manage the host and also manage its behaviour. If we put those three things together in an equation, hopefully in the future we'll come up with something that will buy us more time.” - Sapa-dpa

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