Study Offers Hope for Tasmanian Devils, Once Thought Doomed by Infectious Cancer
In the late 1990s, one affected devil infected an average of 3.5 others, but now each only infects about one
For decades, Tasmanian devils have struggled with a gruesome affliction: a deadly, infectious face cancer that has driven their population from 140,000 in the 1990s to about 20,000 today, Jason Bittel reports for National Geographic. Experts worried that the disease could drive the species to extinction. But new research published today in the journal Science provides some hope: the spread of the cancer has slowed, so it might not wipe the devils out after all.
The researchers analyzed the genetic codes of 51 samples of Tasmanian devil face tumors collected between 2003 and 2018 to figure out how the disease has changed and how fast it spreads. It’s a similar technique to the one used to track the spread of the coronavirus that causes Covid-19, though it had to be adjusted to account for the much larger genetic blueprint of the devils’ cancer. The results show that a Tasmanian devil with the face cancer transmits it to only one of its peers on average, which means that the disease may peter out.
“It is a promising sign for the future,” says University of Tasmania immunologist Gregory Woods, who was not involved with the new study, to Science magazine’s Elizabeth Pennisi.
Behavioral changes and possible disease resistance in the devils, and genetic changes in the cancer, may have contributed in the slower transmission rate, Jonathan Lambert reports for Science News.
Cancers are rarely infectious. There are two other infectious cancers, one in soft-shell clams and another in domestic dogs, per National Geographic. Once a devil catches the face cancer, it is doomed to a slow death as the tumors cause mouth sores that cause the animal to starve. The devils often nip at each other while eating carcasses or during mating season, providing the cancer a chance to spread.
But because the population is now so low, individual Tasmanian devils may be less likely to run into each other. And a study published on December 9 in the Proceedings of the Royal Society B presents evidence that even the most aggressive devils, who would have been “superspreaders” when they were first infected, become secluded as their disease progresses.
“The fact that they behave in this way is likely to have a big impact on disease dynamics,” says University of Tasmania, Sandy Bay, behavioral ecologist David Hamilton, an author of the Royal Society paper, to Science magazine.
When conservation researchers first realized that the Tasmanian devil population was dropping, some established programs to breed the animals in captivity and release them into the wild. But because the wild populations may have reached an impasse with the infectious cancer, the researchers of the Science article argue that releasing more devils may actually cause a resurgence in the disease’s spread. The captive-raised devils may not have the adaptations and resistance to the disease that the wild devils have.
“It sounds boring, but doing nothing might be the best option for the devils,” says lead author and Washington State University evolutionary geneticist Andrew Storfer to Science News.
Aussie Ark conservationist Max Jackson, who helps run a captive breeding program for Tasmanian devils, tells Science magazine that “devils are still not out of the woods.” For instance, there are two strains of the face cancer, but the new research paper only looked at one. And within that one strain, there are five genetic variations, three of which are particularly common. The genetic diversity of the face cancer will make it difficult for scientists to develop a vaccine against the disease.
Devils also face threats from inbreeding due to their small population, as well as habitat fragmentation and deaths by vehicle collisions.
The new research gives conservationists all the more reason not to give up on the scrappy marsupials. University of Sydney conservation biologist Carolyn Hogg tells National Geographic, “Those who work with devils in the wild have been cautiously optimistic.”