Diabolical Evolution against Cancer

Rapid evolution has helped marsupial devils cope with contagious cancer

The marsupial devil takes a sun bath. Wayne McLean / Wikimedia Commons

Australian and American biologists have found out which mutations in the genome of the marsupial devil allowed some animals to acquire resistance to the infectious cancer DFTD (Devil facial tumour disease, "devil facial tumour"), fatal in almost 100 percent of cases. The results of the study are published in Nature Communications (Epstein et al., Rapid evolutionary response to a transmissible cancer in Tasmanian devils).

The marsupial devil is the largest marsupial predator found on the island of Tasmania. Devils spend most of their lives alone and gather in packs when they find carrion, which makes up most of the animals' diet. It should be noted that the devil is an extremely aggressive animal in relation to other individuals of his species, so the joint devouring of food is accompanied by skirmishes. In 1996, the first case of devil's facial tumor was reported, a malignant disease that apparently spreads through bites. For 20 years, the disease has mowed down about 80 percent of the number of devils, in some local populations the mortality rate reached 95 percent. At the beginning of the disease, the devils had lesions and swellings around the mouth, later they developed into malignant tumors that could spread throughout the body. Within six months, the animals died from starvation, internal organ failure or secondary infections. There is no cure for the disease yet, a vaccine based on cells taken from the tumors of deceased animals is currently being developed.

Devils, as they can, resist the disease. Firstly, the animals began to reproduce at a younger age. In 2008, scientists noticed an increase in the percentage of pregnant females under the age of one year, in some populations the increase was more than 80 percent. Up to this point, it was believed that females begin to mate by the end of the second year of life, that is, puberty accelerated by at least a few months. The maximum lifespan of devils is 8 years, so a few months is an impressive period. Secondly, devils began to breed all year round, whereas previously the mating period lasted two months.

The authors of the study found that some populations where the disease has been observed for 10 or more years, contrary to forecasts, did not completely die out, a small percentage of individuals survived. Scientists have taken tissue samples from almost 300 devils from three populations living in different parts of the island. Samples were collected for the first time before the beginning of the epizootic (at least 20 samples in each population), and then several times, at intervals of several years, after the disease spread. The researchers compared sections of the genome and determined which mutations appeared during the course of the disease.

It turned out that the animals had mutations in at least seven genes that in other mammals encode proteins associated with the occurrence of cancer or responsible for immunity. So, there was a mutation in the gene encoding the cerablon protein in humans, which is a target in the treatment of myeloma (a malignant disease of the blood system). The researchers also found mutations in genes that encode proteins that regulate the immune system in other mammals and are involved in intercellular interaction and cell adhesion. The authors of the article suggested that perhaps the devils' immune system "learned" to recognize tumor cells.

The authors of the new work believe that the results they obtained indicate that animals evolved very quickly, within 4-6 generations (at the rate of 1 generation = 2 years). According to the researchers, it is usually difficult to detect breeding in such a short period of time. The discovery is not only of theoretical interest: in 2003, the Australian government created a program to save marsupial devils from complete extinction, designed for 15 years. As part of the program, it is planned to create a population of devils in captivity in order to reintroduce animals into the wild if necessary.

In addition to marsupial devils, transmissible forms of cancer are found in dogs and some species of bivalves. Transmissible venereal sarcoma of canids originated about 11,000 years ago and is usually not fatal for domestic dogs, perhaps because they have managed to adapt to the disease for a long time. Recently, researchers have discovered a contagious form of cancer that affects mussels off the coast of North America. The cause of the disease and the degree of damage to the population are still unknown.

Portal "Eternal youth" http://vechnayamolodost.ru  05.09.2016