SOLUTIONS | 07.31.18
All Eyes on the Devil
Some Tasmanian devils have taken a surprising turn in response to a devastating cancer, offering new hope for the endangered species' survival.
The Tasmanian devil (Sarcophilus harrisii
) is the world’s largest carnivorous marsupial. Despite that distinction, the animal is only about the size of a raccoon. But what the species lacks in heft, it makes up for with tenacity. At night, devils hunt and scavenge wallabies, possums, and other small mammals under the cover of their black fur. During the day, they retreat to underground dens and sleep off the rigors of their nighttime exploits.
As picturesque and wild as northwest Tasmania’s landscape may be, it is also a battleground for disease, and in 2015, Ruiz was patrolling the epidemic front lines. It didn’t take him long to find evidence of the fight. A few dozen paces into the undergrowth, he knelt to inspect a white cylindrical trap nestled amidst a lush cluster of ferns. Inside, a female devil peered down her pointed, whiskered snout at Ruiz. He had seen this individual, nicknamed Leesa, once before. A raw, oozing tumor as large as a ping-pong ball gaped behind the right corner of her mouth—the mark of a debilitating cancer.
Since then, some wild devils have begun to show signs of resistance, offering new hope for the species’ survival. And while the quickly spreading cancer has wrought great devastation, it has also offered scientists a rare window into the progression of cancer at large. Researchers are monitoring the disease as it runs its course, searching for clues that will help them derail it. They’re hopeful that their findings might soon be applied to combatting cancers in other species—maybe even in humans someday.
Most cancers arise within their hosts and die along with them. But some are infectious, shuttled by agents like viruses (as in California sea lions), bacteria, or other microscopic vehicles. In devil facial tumor disease, the cancer cells themselves are the infectious agents—making the tumors transmissible from one individual to another. Transmissible cancers are not well understood, partly because they only recently landed on researchers’ radar screens. Of the eight known transmissible cancers identified so far in devils, dogs, and marine invertebrates, seven were detected within the past three decades.
Scientists from government agencies and research institutions across Tasmania are tracking how devil populations fare in the wake of the cancer’s swift spread. Monitoring teams routinely visit sites across the island, staggering their data collection geographically to complement one another. Ruiz, who is a member of the University of Tasmania team, tracks the devil’s physiological response at several sites stricken by cancer in the northwest region. Out in the field, he and his colleagues snap mugshots of all individual devils they capture, which, when viewed as a collection, are reminiscent of a Most Wanted poster. Along with tissue samples, these photos allow the team to assess tumor growth over time.
The scientists also analyze blood samples to chart the devils’ immune response as the cancer progresses. “We can be collecting blood samples, and the devils are just snoring away without a care in the world,” says Ruiz, who has trapped, micro-chipped, and tracked more than 400 devils. “They seem like a little teddy bear when they’re asleep—but with big jaws that can chop your finger off at any time.”
Even perfectly healthy devils are short-lived: Most individuals live just six years. Since the cancer’s outbreak two decades ago, several generations of devils have come and gone, and that short generation time may confer a selective advantage. People often think of evolution as happening over thousands or millions of years, but, according to Ruiz, it's happening right now in Tasmanian devils and their cancer. “This is one of the most interesting systems in the world for understanding the evolution of pathogens and their hosts,” Ruiz says.
The scientific community was buoyed by the promise of this finding. But the trials had their limitations. Sample sizes were small, and vaccinated individuals released into the wild were sometimes difficult to catch again, making it a challenge to measure the vaccine’s effectiveness. Additionally, most of the animals that were eventually recaptured came back with malignant growths, indicating that while the vaccine could stimulate the immune system to produce tumor-fighting antibodies, it wasn’t protecting the devils from contracting cancer in the wild.
“There’s something that might make devils more susceptible to disease,” says Rodrigo Hamede, a research fellow at the University of Tasmania, and one of Ruiz’s advisors, who studies the ecology of transmissible cancer. According to Hamede, the emergence of a second transmissible cancer in the same species is rare and raises many questions about the perfect storm of factors that has targeted devils twice in just 20 years. He hopes to identify what makes devils susceptible; his findings may shed light on whether we could see a transmissible cancer emerge in humans someday.
Once raw and red, the lump on her right cheek now gleamed with healthy tissue. Ruiz thumbed through Leesa’s previous datasheets in excitement to confirm before phoning Hamede from the field: Leesa’s tumor had naturally regressed. Somehow, she had developed antibodies to fight the disease.
Leesa was not the first wild devil to show spontaneous tumor regression. The University of Tasmania team had detected six other individuals with naturally regressing tumors before Leesa’s case was documented. Since then, eight more animals—a total of 15 devils at northwest monitoring sites—have shown signs of regression. And other individuals are simply living longer with their tumors; although transmission rates have remained high in northwest Tasmania, mortality rates and the overall devil population in the region have stabilized.
Armed with this information, scientists have been working to understand why some individuals are responding differently to the disease. Two years ago, a team that included Hamede looked at whether the species could be evolving natural mechanisms to combat devil facial tumor disease. They compared individuals from three sites across Tasmania, all born four to six generations after the cancer’s outbreak, and detected rapid changes in their genomes; two regions of genetic code in particular looked different. These regions contain genes that are known to influence cancer risk and immune function in humans—suggesting that devils could be evolving resistance. If scientists can firmly establish that certain devils have evolved resistance to the cancer, they may be able to accelerate the recovery of the species by introducing immune individuals into populations that currently lack genes for resistance.
Meanwhile, Woods’s team continues working to develop a vaccine that can prevent devils from contracting facial tumor disease. In the most recent trials, the team vaccinated more than 50 disease-free individuals from insurance populations and released them into the wild. Some animals were fitted with GPS collars to allow for higher recapture success and follow-up immunizations. The study found that 95 percent of vaccinated individuals produced antibodies that combat the disease.
The next step is seeing whether the vaccine can be strengthened in a way that would lead to tumor regression and keep devils from contracting facial tumor disease in the first place. The team remains optimistic that in the not-too-distant future, captive devils destined for the wild might be released with full immunity to the disease. These introductions will bolster wild populations that are still hanging on, despite the dire predictions issued a decade ago.
Ruiz last trapped and released Leesa in August of 2016, when she was an elderly 7 years old. While he assumes she no longer patrols the eucalyptus forests of northwest Tasmania, he feels strongly that Leesa likely died of old age or another natural cause—not from cancer.
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ABOUT THE Photographer
Heath Holden is a Tasmanian-born photographer and photojournalist. For the past five years, Holden has been photographing the Tasmanian devil in the wild using camera traps and documenting conservation efforts within the state. He is currently on assignment in the Middle East but plans to take the devil work to the next stage upon his return to Tasmania. Holden is a contributor to Getty Images Editorial APAC along with many other national publications.
ABOUT THE Writer
Katie Jewett is a science writer at the California Academy of Sciences, where she loves learning something new every day about our planet. Previously, she spent winters in the Colorado Rockies and summers living and working on the water. Follow her on Twitter @ktjewett
Heath Holden Katie Jewett
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