Tasmanian devils develop cancer resistance

A deadly, infectious facial cancer has decimated Tasmanian devil populations and is driving them toward extinction, but a new study suggests they are rapidly developing resistance to the disease.

A comprehensive international study of the genomes of 294 devils before and after the virulent cancer came to light 20 years ago, revealed species-wide adaptations in seven genes in just four to six devil generations.

Five of those genes are linked to immunity and cancer resistance in mammals, according to the international study, published August 30 in the journal Nature Communications.

"The devils are evolving," study co-author Andrew Storfer of Washington State University told AFP. "Remarkably, this evolution was quite rapid."

The results were especially surprising, say the scientists, as species evolution through the acquisition of lasting and beneficial genetic traits in response to factors such as environment or disease is generally thought to be a long, slow process.

Surviving against the odds

Scientists first noticed tumors growing on the faces of Tasmanian devils in 1996. Since then the cancer has spread across the Australian island of Tasmania, wiping out up to 90 percent of the dog-sized nocturnal marsupials in some places.

Most cancers die with their host. In vertebrates, just two known types - Devil Facial Tumor Disease (DFTD) and Canine Transmissible Venereal Cancer - are contagious. DFTD in devils is nearly 100 percent fatal and is spread when the aggressive animals bite one another. Those infected often die of starvation as the facial tumors prevent them from eating.

Some experts had predicted that the species would be extinct by now. Intrigued as to whether genetics was playing a role in their survival, evolutionary geneticist Storfer teamed up with colleagues from the United States, the United Kingdom and Australia to investigate.

"If a disease comes in and knocks out 90 percent of the individuals, you might predict the 10 percent who survive are somehow genetically different," said study co-author Paul Hohenlohe, assistant professor of biology at the University of Idaho. "What we were looking for were the parts of the genome that show that difference."

Vital to ecosystem

The scientists still have to confirm that the gene changes observed do actually boost resistance in the animals. The results could then be used to breed devils carrying the resistant genes and contribute to research on cancer.

"Our study suggests hope for the survival of the Tasmanian devil in the face of this devastating disease," Storfer said in a statement. "Ultimately, it may also help direct future research addressing important questions about the evolution of cancer transmissibility and what causes remission and reoccurrence in cancer and other diseases."

Tasmanian devils have been the top marsupial predator on the island since the Tasmanian wolf or thylacine died out in the 1930s. Their loss would be bad news for other wildlife there.

"The Tasmanian devil is too important to lose," wrote the study authors in non-profit media outlet, The Conversation. "Since the thylacine's extinction, devils have stepped up to the role of top marsupial predator, keeping numbers of destructive feral cats at bay in Tasmania. With the decline of the devils, invasive species have become more active."

jc, mlr/gw (AFP)