Biologists ‘canceled’ the extinction of Tasmanian devils due to contagious cancer

New data show that the disease of a transmissible facial tumor in Tasmanian devils has entered an endemic phase: animals have adapted to the most dangerous disease, and now it is unlikely to threaten them with extinction.

Humans almost destroyed the marsupial Tasmanian devils, and only strict measures to protect this rare predator have preserved its populations in Tasmania and Australia. However, in recent years, the Tasmanian devil has been pursued by a new attack that threatens the species with complete extinction – a malignant facial tumor transmitted from individual to individual by contact, through bites.

In the late 1990s, when a vector-borne tumor was first noticed, it was highly lethal and “contagious,” spreading rapidly across populations. However, this trend has unexpectedly slowed down in recent years: the disease is transmitted more slowly and is easier to carry. It seems that brutal selection made the Tasmanian devils adapt; this is reported in a news article published in the journal Science.

The authors of the work – Andrew Storfer of the University of Washington and his colleagues – note that previously a sick animal managed to infect an average of three to four relatives. Still, now this figure has dropped to one. Genetic analysis of tumors obtained in different regions and at different periods of time confirmed that their spread, previously almost uncontrolled, slowed down. From an epidemic form, the disease became endemic.

According to scientists, there are at least three reasons for this. First, the epidemic has thinned out the animal population, making it difficult to spread itself (contagious cancer has been responsible for 75 percent of the decline in animal populations since the 1990s). Secondly, the Tasmanian devils themselves could adapt and breed new generations slightly more resistant to transmissible tumors. Finally, cancer, having mutated many times during this time, could become less dangerous. This is also indicated by spontaneous reduction and sometimes complete disappearance of facial tumors, which are sometimes observed in these animals today.

Scientists emphasize that now the complete extinction of Tasmanian devils due to vector-borne cancer can be called unlikely. Rather, the animals will coexist with the disease for some time until it disappears itself.

However, some outside factors can dangerously alter the balance of power. To support the few wild populations of Tasmanian devils, today they often release individuals bred in zoos. As the descendants of parents who have not had contact with transmissible cancer, they can become easy prey and “base” for his survival.

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