The Unfolding of a Disaster
In 1996, photographer Christo Baars snapped some disturbing Tasmanian devil images in northeastern Tasmania. The faces of the devils that he captured on film were hideously distorted. He’d never seen anything like it. His friend, government zoologist Nick Mooney, passed the photos on to his colleagues, who hadn’t seen such damaged devils before either. Perhaps this was a cancer caused by some environmental factor, they thought.
Fast-forward to 1999. Tasmanian ecologist Menna Jones, who hadn’t heard about Christo’s photos from three years before, checked some traps she’d set in the wild for Tasmanian devils. Moving along the trapline, she was shocked. “As I got closer to the northern end of the trapline,” Menna says, “I saw that about a third of the devils had these horrendous growths on their heads. I didn’t have a camera with me and I didn’t collect samples. I just didn’t have time to follow it up right away.” Menna continues, “In 2001, I trapped three devils with the huge tumors and took photos. I was the first biologist to see and then photograph the disease in the wild.”
From then on, Menna kept track of the horror’s spread. “In January 2002, I picked up the disease 6.2 miles [10 kilometers] south of the previous finds, giving us the first data that showed the disease was spreading.” Then, in July 2002, only six months later, Menna saw a 60 percent drop in the devil population; where she had once trapped sixty animals, she now found only fourteen. And nearly all the adults she found had the disease. In 2003, Menna’s colleague Nick Mooney found very few devils in the northeast. The whole area seemed to have lost its devils. Nick Mooney and Dr. Marco Resani also found that the disease had spread widely in the center and east of the island.
Farmers were also reporting that fewer devils seemed to be around. Devils hunt prey, but they are also excellent scavengers, and the carcasses of dead sheep and cows on northeastern farms were often untouched. By then it was clear that the disease somehow passed from one animal to another, it was spreading fast, and it was deadly. What was going on?
By 2003, scientists had named the plague “Devil Facial Tumor Disease.” In 2004, the Australian and Tasmanian governments set up the Save the Tasmanian Devil Program, which in 2005 began capturing animals from areas that were still free of disease to create “insurance populations” in zoos and wildlife parks. If scientists’ worst fears were realized and the disease wiped out all the wild devils, then these captive animals, or their future offspring, might be released into the wild so they could repopulate Tasmania. Research also intensified into how devils live in the wild and into whether a vaccine could be developed to protect them from the disease.
Their concern was warranted—devil populations plunged by as much as 95 percent in areas the disease reached, which included most of Tasmania. The disease seemed to be 100 percent fatal. But until scientists knew the cause, how could they find an effective treatment or know how to protect animals from becoming infected?
Finding the Cause
Jenny Graves’s phone rang in the winter of 2005 (summer in the Northern Hemisphere). On the other end was fellow geneticist Anne-Maree Pearse from Hobart, Tasmania. “I’d like to see what you think of my photographs of Tasmanian devil tumor cells. Could I come and see you? Don’t tell anyone,” she said.
“I was intrigued,” Jenny said. “I’d never looked at devil chromosomes, but I knew they were just about the same across many related species.”
A few days later, Anne-Maree arrived at Jenny’s lab. Jenny recalls, “She spread out her karyotypes [chromosome photographs taken using a microscope] of chromosomes of both normal animals and animals with the tumors. When I looked at her images, I nearly fell off my chair. The tumor chromosomes were weird, containing one superlong chromosome, and with no sign of sex chromosomes. Weird chromosomes are quite standard for solid tumors in humans. The amazing thing about these was that the chromosomes from tumors from different animals were all the same!”
Anne-Maree confirmed that, yes, the chromosomes were from tumors found in different devils, even though they all looked the same.
“You may think I’m crazy,” Jenny said to Anne-Maree, “but I think you must have a cell clone.”
Jenny explained to me, “I realized that somehow a devil tumor cell was jumping from one animal to another. Not a virus or a bacterium. This was an unprecedented concept, but there was really no other explanation. Anne-Maree was very receptive to the idea; I think she’d already come to this conclusion but needed confirmation.”
Anne-Maree and her assistant, Kate Swift, published their discovery in 2006, proposing that one animal had developed the cancerous tumor. Normally the immune system of another animal would recognize the tumor cells as “other,” coming from a different individual, and destroy them. But somehow, these cells were able to establish themselves and grow into deadly tumors that could then be passed on to other unfortunate devils through biting.