There is renewed hope for the survival of endangered Tasmanian Devils after a large number of facial tumors have been killed.
The world's largest carnivorous marsupials have been fighting Devil Facial Tumor Disease (DFTD) for more than 20 years.
But researchers have found that the animals' immune system is modified to combat the attack.
And according to an international team of scientists from Australia, Britain, the US and France, the future looks better for the devils now.
"In the past, we managed vicious stocks to prevent extinction, and we are gradually moving toward an adaptive management strategy to improve these selective adaptations for the development of devil / DFTD coexistence," explains Drs. Rodrigo Hamede, dr. University of Tasmania.
The disease was first discovered in 1
The team of dr. Hamede has collected epidemiological evidence in the last 10 years. The group has presented scenarios based on current infection rates in the wild, and in their forecast for the next 100 years, 57% of the scenarios consider hiding DFTD and 22% coexisting.
How does the disease spread?
The disease is transmitted when devils bite their faces during fighting.
The biting behavior is a way to socialize and enforce the dominance that, in addition to the growling cries, helped to give the devils their nickname.
"Our current hypothesis is that biting not only leads to the spread of tumors but is also the starting point," explains Max Stammnitz of the University of Cambridge, UK, who sequenced tumor genome.
"If the scarring processes for the recurring wounds are interrupted by a mutation, it can become a cancer, they do not heal and grow into an outer tissue that then becomes transmissible," says Stammnitz.
After the bite, a solid tumor grows around the face or neck, with the force to break bones in the jaw – the animal is killed after 6 to 24 months.
To make the crisis worse, in 2014 a second transmissible cancer (DFT2) was detected in wild populations in the south of the island.
"A second transmissible tumor in devils was extremely surprising, as if a lightning struck the devil twice," Dr. Hamede.
But in the past 5-6 years, some devils have developed a higher tolerance to infections and even resistance without human intervention, which means that although the population numbers did not recover to the pre-DFTD numbers, the Decline, however, has at least declined.
How does natural selection help?
"Natural selection tries to solve the problem by favoring those who can survive the tumor, so we are more hopeful than ever," he explains. Hamede.
Every three months, the international team monitors eight locations in the east, south and west of the island, observing several generations of devils.
"We have seen how these tumors affect the ecology of devils and how they evolved in real time with their hosts," says Dr. Hamede.
Devils can now adapt to transmissible cancer at the genetic and phenotypic levels – meaning of the DNA and features of the gene characteristics. This is due to their phenotypic plasticity – the ability of a single organism to alter its physiology or gene expression in response to changing environmental conditions. Even more unique is how fast this happened – in just 16 years, in only eight devil generations.
"It's a constant arms race of adaptation between animals and diseases, and we're developing mechanisms of resistance that put the pathogens under pressure to improve the infection," says Stammnitz.
The first of these mechanisms is tolerance and the second is resistance.
The team has found devils who have lived with the disease for up to two years, so that two more litters can be used to recruit the population.
In addition, 23 cases of tumor regression have been found so far – devils also have the ability to fight and recover from DFTD.
What is the future for the devils?
The second biggest threat to devils is roadkill, with at least 350-450 devils every year, according to Dr. Fox was killed by the Save the Tasmanian Devil Program (STDP).
The STDP has targeted hotspots and installed fences that raise the alarm and warn the wildlife of approaching cars. The current path has led to a 50% reduction in roadkill since 2015.
Devils have fallen by a quarter, and the Tasmanian Pademelons and Bennetts Wallabies have benefited as well.
The government has also been following a new app since July that allows members of the public to report sightings to monitor the population.
So far, the app has been downloaded by over 2,000 users who have entered 6,000 reports.
"When we tracked the start of the DFTD in 2003, street kill reports informed the public of our knowledge of where it had spread and showed the power of citizen science to help the devils," adds Dr. Fox added.
In the curious case of the Tasmanian Devil, much remains to be learned about cancer biology and the evolutionary arms race between malignant cells and their hosts.
The sheer speed of the decline has exerted a strong selective pressure on the world's largest remaining carnivorous marsupial, but there now seems to be hope for coexistence.