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Resistance to DFTD could save the animals from extinction
Over the past twenty years, an infectious form of cancer has spread to wild Tasmanian devils. The disease spreads quickly and more and more animals die from DFTD. Conservationists and veterinarians have been looking for ways to prevent the extinction of animals known as pouch devils for a long time. Researchers have now found that the devils are evolving rapidly to build resistance to cancer.
A team of scientists found that the so-called Tasmanian devil is developing resistance to the common, deadly form of cancer. This may save the Tasmanian Devil himself from extinction. The doctors published the results of their study in the journal "Nature communications".
DFTD is transferable
Cancer usually develops in a host and then dies with it. Vertebrates have two known types of cancer that develop differently. The so-called Canine Transmissible Venereal Cancer in dogs and Devil Facial Tumor Disease (DFTD) in Bag Devils. These types of cancer have developed an extraordinary mode of transmission in the course of evolution. The cancers do not only grow in a single host. They can spread to other animals. Because these cancer cells are all derived from a mutated cell, the cancer is virtually immortal, the researchers say. Another study previously found that some animals can transmit cancer. Not only dogs and marsupials can transmit cancer, mussels are also able to do this.
Pouch devils develop resistance to DFTD
To grow in the new host, the tumor cells must prevent recognition and rejection by the immune system. The cancers transmitted by the devil and dog have developed sophisticated mechanisms to escape the host's immune system, the experts explain. The results of the new research suggest, however, that the bag devil is resistant to its deadly disease.
Pouch devil important for containment of invasive species
The Tasmanian Devil does an important job. For example, the marsupial helps to contain the number of destructive wild cats on the island of Tasmania. With the advancing extinction of the marsupial invasive species became more and more active, say the scientists.
Bag devil populations have decreased by 80 percent
DFTD was first discovered in the northeast of Tasmania in the mid-1990s. In the meantime, this type of cancer has slowly spread to the south and west over the years, say the doctors. In a few years, all parts of Tasmania will be affected by the disease. Only the north-west coast of Tasmania and parts of the south-west are currently free of epidemics. Since the DFTD spread, the bag devil populations have declined by at least 80 percent, the experts explain. In some areas, more than 90 percent of the animals died in a local disease outbreak within six years.
Bag devils have fewer and fewer offspring
Most pouch devils die of DFTD during their sexual maturity. Before the fatal cancer, the devils usually produced offspring three times in their lives. Most Tasmanian devils now have only one offspring.
Effects of the extinction of pouch devils
The extinction of the marsupial would have a major impact on the rest of the ecosystem. Other species may be lost. For example, wild cats have already increased their activities, and the populations of small mammals that serve as prey for cats have already declined accordingly.
Significant changes in DNA found in bag devils
Andrew Storfer from Washington State University and Paul Hohenlohe from the University of Idaho examined the data of the poison devil genes. This data came from before DFTD occurred and about 8 to 16 years after DFTD spread. We identified significant changes in Devil's DNA samples in two small regions. DFTD is widespread in these regions, the scientists say. Five out of seven genes in the two regions were related to cancer or immune functions in other mammals. This suggests that the Tasmanian Devil is actually developing resistance to DFTD, the authors say. Evolution is usually a very slow process. The changes noted would occur four to eight generations after the disease first broke out.
What does the rapid development of the bag devil do?
So far, our studies have shown that at lower rates of DFTD bag devils show certain changes in their immune response. The new genetic results could now provide an explanation for this, the experts speculate. Rapid development requires existing genetic variation. Our results are surprising because the Tasmanian devils actually have little genetic diversity, the researchers add.
DFTD is also evolving
Development is not only evident in the devils. The disease also continues to develop. DFTD no longer tries to kill the host before it has spread to a new host. In addition, the disease tries to overcome its host's defenses through its development, the experts explain.
With DFTD, we may be able to understand how cancer can become communicable
Our results suggest that evolution will save the Tasmanian Devil from DFTD. However, it is important to develop strategies that help the bag-devil in their struggle to survive, the doctors say. In addition, DFTD is a unique opportunity to study the early stages of developing a new disease and communicable cancer in its animal host. This research enables us to understand how cancer can become transmitted and how the affected hosts react to it, the authors explain. (as)