Tasmanian Devils May Be Evolving To Live With The Cancer That's Killing Them

Devils use biting to assert dominance but scientists believe the behavior is what causes DFTD. Susan Flashman/Shutterstock

Tasmanian devils (Sarcophilus harrisii) are tough little creatures that demonstrate their reckless ferocity by literally ripping chunks from opponents' faces. They are the Jason Statham of the animal kingdom, possibly only rivaled by the honey badger (Mellivora capensis) for their pure IDGAF attitude.

But for the last 20 years, they have been under attack – not from a predator, but from a condition called Devil Facial Tumor Disease (DFTD). Indeed, the disease has been so damaging to the Tasmanian devil community that it has put their survival as a species in jeopardy.

An already dire situation was made even worse when, in 2014, experts discovered a second type of transmissible cancer (DFT2), threatening animals in the south of Tasmania.

Fortunately, a process of adaption and natural selection appears to be enabling the animals to live with their condition, a paper published by the Ecological Society of America (ESA) suggests. According to Rodrigo Hamede from the University of Tasmania, the immune system of some devils has changed to fight DFTD.

For the study, Hamede and his team predicted the long-term impacts of DFTD using computer models based on 10-years' worth of epidemiological data from across the island. These models allowed them to calculate the likelihood of three possible scenarios taking place in the next 100 years: one, DFTD drives the devils to extinction; two, DFTD vanishes and the species survives; and three, DFTD and the devil evolve to the point where they can co-exist. 

Out of 122 possible scenarios, one in five (21 percent) led to devil extinction, whereas the majority (57 percent) led to DFTD vanishing. The remaining 22 percent resulted in DFTD-devil co-existence. 

"In the past, we were managing devil populations to avoid extinction," Hamede told the BBC.

"Now, we are progressively moving to an adaptive management strategy, enhancing those selective adaptations for the evolution of devil/DFTD coexistence."

This adaption appears to have cropped up sometime within the last five or six years, providing some devils with a higher tolerance to infection and, possibly, even resistance. It's a perfect example of natural selection working "to fix" a problem, with those displaying a higher tolerance able to survive the tumor and reproduce, propagating the desirable genetic traits.

The researchers report multiple instances of infected devils living up to two years with the disease, allowing them to reproduce twice more and pass on their tolerance-promoting genes. On top of that, there have been 23 cases of devils recovering from DTFD completely.

While the Tasmanian devil population has not bounced back to pre-DTFD numbers, the good news is that it does seem to have leveled out.

What is incredible is the speed at which this is adaption happening. The ability to tolerate and resist the infection developed just 16 years (or eight generations) after DFTD was first described in 1996. This is thanks to the species' phenotypic plasticity, which basically means an individual is able to change its physiology or gene expression in reaction to its environment.

Not only is this extremely promising for the future of the devil in Tasmania, it may even help scientists understand our own relationship with cancer, Frederic Thomas, study co-author and a researcher at the Center of Ecology and Evolution of Cancer in France, told Nat Geo.

For now, we're just happy that things are looking up for these feisty little creatures.

Tasmanian devils may have the strongest bite of all living mammals, but they are actually quite peaceful when they are not feeding or mating. worldswildlifewonders/Shutterstock

 

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