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The most extensive genetic analysis of mountain gorillas ever conducted has found the critically endangered apes burdened with severe inbreeding and at risk of extinction but the researchers still see reasons for optimism about their survival. Twenty-three scientists from six countries on Thursday unveiled the first complete genetic map of the mountain gorilla, a close genetic cousin to humans inhabiting two isolated areas in central Africa. "We found extremely high levels of inbreeding," said geneticist Chris Tyler-Smith of Britain's Wellcome Trust Sanger Institute. The study in the journal Science revealed a substantial loss of genetic diversity from inbreeding caused by mating with close relatives due to small population size. Inbreeding can increase threats from disease and environmental change by reducing the genetic ability to adapt and cause a larger hardship of harmful mutations.
"Mountain gorillas are critically endangered and at risk of extinction, and our study reveals that as well as suffering a dramatic collapse in numbers during the last century, they had already experienced a long decline going back many thousands of years," University of Cambridge geneticist Aylwyn Scally said.
But in some cases inbreeding was helpful because it weeded out harmful genetic variations. "It is a small population, and there is inbreeding, but the study reveals some of the inbreeding was positive and got rid of a number of the deleterious genes,” said co-author Mike Cranfield, co-director of Gorilla Doctors, a partnership between the UC Davis Wildlife Health Center and the nonprofit Mountain Gorilla Veterinary Project.
The researchers were surprised that many of the most harmful mutations, those that can stop genes from working and cause serious health conditions, were less common than in other gorilla subspecies. "We have shown that although low in genetic diversity they have not yet crossed any genetic threshold of no return. They can continue to survive and will return to larger numbers if we help them," Scally said.
There are only about 880 mountain gorillas in the world, living in mist-covered forests of the Virunga volcanic mountain range on the borders of Rwanda, Uganda and the Democratic Republic of Congo and Uganda's Bwindi Impenetrable National Park. The researchers said the main threats to these animals are from humans: habitat loss, hunting and diseases transmitted from people.