The endangered gorilla Grauer has recently lost genetic diversity and has experienced an increase in harmful mutations. These conclusions were made by an international group of researchers who sequenced eleven genomes from samples of the eastern gorilla collected up to 100 years ago and compared them with the genomes of modern individuals. The results are now published in Current Biology,
Over the past century, the numbers of many wild animals have declined, and scientists have long been concerned that these cuts have led to a loss of genetic diversity, an increase in inbreeding, and an accumulation of harmful mutations. While this may lead to an even greater risk of extinction in endangered species, the study of recent changes in genetic viability has been difficult. In a new study, a group led by scientists from Uppsala University and the Swedish Museum of Natural History used samples stored in museum collections to analyze changes in the genomes of the eastern gorilla over the past 100 years.
“We found that the genetic diversity of the Gorwell gorillas was significantly reduced in just a few generations,” says Tom van der Valk, a graduate student at Uppsala University in Sweden.
Gorilla Grauer are found in the Democratic Republic of Congo, and over the past decades their number has decreased by 80 percent due to poaching and habitat destruction. The results of the comparison of historical and modern genomes show that this decrease led to an increase in inbreeding and a loss of genetic variability. This, in turn, means that Grauer's gorillas probably have become less able to adapt to future outbreaks of disease and environmental changes. In addition, scientists have identified several mutations that are likely to be harmful and have increased in frequency over the last 4-5 generations as a result of a decline in the population. However, in the closely related mountain gorilla, scientists have not found any significant genetic changes, suggesting that its genetic viability has remained stable for the past 100 years.
“This recent increase in the number of harmful mutations really underlines the need to reverse the reduction in the number of Gorwell’s gorillas,” says Love Dalen at the Swedish Museum of Natural History.
Some of the potentially harmful mutations that increased in frequency were found in genes that affect disease resistance and male fertility. In addition, the researchers identified mutations that lead to loss of function in the genes associated with the development of fingers and toes, which probably explains why modern gorillas sometimes have fusion digits.
“Our study emphasizes that historical museum exhibits are a unique resource for monitoring recent changes in the genetic status of endangered species,” says Katerina Guschansky of Uppsala University.
Interestingly, the reason why the gorillas of Grauer suffered more than the mountain gorillas may lie in their deeper history. While Grauer's gorillas increased significantly in numbers between 5,000 and 10,000 years ago, mountain gorillas were rare for several thousand years. This prolonged small population may have allowed natural selection to eliminate harmful mutations before the number of mountain gorillas began to decline in the 20th century.