Mountain gorillas are large primates critically endangered living in central Africa, but they are adapted to survive in small groups, according to an international research that has sequenced the genome from different gorillas to compare the genomes of all four Gorilla subspecies.

The main objective has been to assess the genetic impact of long-term population decline. The results suggest that, thanks to inbreeding, lots of deleterious genetic variation disappeared from the population, that fact contributed to the survival of the group.

These are some of the conclusions of the research, involving researchers from the Institute of Evolutionary Biology, mixed centre of Centre of Scientific Research (CSIC) and Pompeu Fabra University, and National Genome Analysis Centre. The results are published in the magazine Science.

At first we thought that the low level of genetic diversity produced by the inbreeding could make, that mountain gorillas were more susceptible to environmental changes and endemic diseases, including infectious strains of human viruses. However, inbreeding has genetically benefited to these species.

"These data show us the genetic derivation and the process by which genomes create mechanisms to eradicate deleterious recessive mutations," says the research leader, Chris Tyler-Smith, Institute Sanger researcher (United Kingdom).

Researchers have analysed gorillas genes and they have found that there are less harmful variations in mountain gorillas than in other western populations, which are more numerous. These variations can cause important health problems.

"Three years after the first sequenced of an individual reference genome, followed by the one of Copito de Nieve, and then by more than 30 gorillas genomes, now we can compare the genomes of all four Gorilla subspecies, including the mountain gorilla, and we can also start to understand their similarities and differences, and the genetic impact inbreeding", adds the doctor Tomas Marques-Bonet, researcher at Institute of Evolutionary Biology and at the National Genome Analysis Centre.

The number of mountain gorillas living in Virunga volcanic mountain on the borders of Rwanda, Uganda and the Democratic Republic of Congo fell to 253 in 1981 as a result of hunting and habitat destruction. Since then the number has increased to 480, thanks to the conservation efforts of different organizations.

"This new understanding about the genetic diversity and the demographic history of gorillas populations provided to us a valuable information about how apes and therefore humans are genetically adapted to live in small populations," says Aylwyn Scally, from Cambridge University.

"We are worried that the drastic decline in the 80's were catastrophic to mountain gorillas in long term, but our genetic analysis suggest that gorillas have faced to small populations size during thousand of years, more than expected", says Javier Prado-Martinez, from Institute of Evolutionary Biology.

"Despite similar levels of inbreeding contributed to the extinction of Neanderthal, mountain gorillas can be stronger. There is no reason for them not to have survived in those conditions during thousand of years", adds Prado-Martinez.

Genomic data collected in this researcher can help to conservation efforts. Thanks to a detailed analysis of genetic differences between populations, it will be possible to identify the origin of gorillas that have been caught or illegally killed, according to researchers. This fact will let gorillas to be back in their natural habitat and it will make easier bringing illegal hunters to justice.