Mountain gorillas (Gorilla beringei beringei) are among the most iconic endangered species in the world and, as such, have become a prominent focus for conservation.
Surviving in only two small and fragile populations in central Africa, there are currently estimated to be about 800 individuals, with just over half living in three national parks on the Virunga mountain range.
The Virunga population of gorillas was made famous by primatologist Dian Fossey’s book and subsequent film, Gorillas in the Mist. Numbers have doubled from a low point of about 253 gorillas in 1981 thanks to conservation efforts and support from the public, but they remain at risk of extinction.
The drop in population size led to extensive inbreeding which raised concerns that a small gene pool could harm the gorillas' long-term future, particularly their ability to survive infectious diseases and cope with environmental change.
But little work has been done on their genetics, or to establish how they evolved from eastern gorillas (G. beringei).
Now scientists have discovered inbreeding has actually benefitted mountain gorillas by removing many harmful genetic variations. They are also genetically adapted to living in small populations.
The authors of the findings, published in the journal Science, said it is the first project to sequence whole genomes from mountain gorillas.
Gorillas have been coping with small population sizes for thousands of years
"We worried that the dramatic decline in the 1980s would be catastrophic for mountain gorillas in the long term, but our genetic analyses suggest that gorillas have been coping with small population sizes for thousands of years," said lead author Dr Yali Xue, from the Sanger Institute.
"While comparable levels of inbreeding contributed to the extinction of our relatives, the Neanderthals, mountain gorillas may be more resilient. There is no reason why they should not flourish for thousands of years to come."
The whole genomes of seven mountain gorillas and six eastern lowland gorillas (G. b. graueri), the other sub-species of eastern gorilla, were sequenced using blood samples collected over several years.
Both sub species were found to be two to three times less genetically diverse than the more populous western lowland gorillas (Gorilla gorilla gorilla).
Fewer harmful genetic mutations, which stop genes functioning and can cause serious health conditions, were found in the mountain gorilla population than in the western gorilla populations.
Researchers also discovered that mountain gorillas have survived in small numbers for far longer than previously thought, with the average population size being in the hundreds for many thousands of years.
“We were wondering what kind of results the researchers would find. We were thinking this could really be the end of the gorilla despite all of our efforts, so this is really a great surprise and great news for us,” said Dr Tony Mudakikwa, head veterinarian for the Rwanda Development Board, which manages the country’s national parks.
The authors hope the work will help inform future conservation efforts and research. Conservation organisations say it will also make it possible to trace where dead or injured gorillas have come from, allowing more of those that are rescued to be returned to the wild and making it easier to bring prosecutions.
“The fact we think the genetic health of the population hasn’t been damaged by the decline it went through is just amazing, and eliminates the need of possibly introducing outside genes to recuperate the population,” said Dr Mike Cranfield, director of the Mountain Gorilla Veterinary Project, the scheme that collected many of the blood samples used in the study.
“We have to continue collaborating with other small, isolated populations of gorilla to put all of the pieces of the puzzle together to make a consistent and viable approach to the conservation of the eastern gorilla.”
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