Mountain gorillas show signs of severe inbreeding, suggesting the species may be caught in a genetic bottleneck, according to a new study. These animals are critically endangered, and such extreme inbreeding may be creating an additional risk for their future survival, researchers believe.

An international team of 23 researchers representing six nations recently completed mapping of the complete genetic code of mountain gorillas. This new research is the most extensive analysis ever performed of the genetic structure of the species.

Mountain gorillas are closely related to human beings but are now confined to just two locations in the world, including the Virunga volcanic mountain range which borders Uganda, Rwanda and the Democratic Republic of Congo.

"Mountain gorillas are among the most intensively studied primates in the wild, but this is the first in-depth, whole-genome analysis. Three years on from sequencing the gorilla reference genome, we can now compare the genomes of all gorilla populations, including the critically endangered mountain gorilla, and begin to understand their similarities and differences, and the genetic impact of inbreeding," Chris Tyler-Smith of the Wellcome Trust Sanger Institute in Britain said.

Blood samples taken over the course of several years through programs of the Rwanda Development Board and other organizations were examined to read the DNA record. Analysis of the genome of seven gorillas revealed that the mountain gorillas, as well as their neighbors, eastern lowland gorillas, are two-to-three times less genetically diverse than other species of the primates from nearby regions.

Populations of mountain gorillas in the Virunga mountain range dropped to just 253 individuals in 1981 as a result of hunting and the loss of their native habitat to human encroachment. Today, biologists believe there may be as many as 480 of the animals left in the region.

Inbreeding can cause several problems for the gorillas, including an increase in the incidence of certain birth defects. Resistance to some diseases can be reduced in populations, as well as the ability to withstand the effects of changes in habitat. However, while it makes them more vulnerable to disease, researchers noted "the inbreeding has, in some ways, been genetically beneficial. Fewer harmful loss-of-function variants were found in the mountain gorilla population than in the more numerous western gorilla populations. These variants stop genes from working and can cause serious, often fatal, health conditions."

"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," Aylwyn Scally, a geneticist with the University of Cambridge, said.

Dian Fossey, a primatologist who studied mountain gorillas, helped to raise awareness of the challenges faced by the species through her 1983 book, Gorillas in the Mist, which was later adapted into a widely popular documentary film. The populist wildlife researcher was murdered in 1985.

Investigation of inbreeding among mountain gorillas and the role played by meager populations in ensuring continued population growth was published in the journal Science.

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