The endangered Grauer Gorilla has recently lost genetic diversity and has experienced a dangerous increase in mutations. This conclusion was reached by an international research team that sorted eleven genomes from eastern gorilla specimens collected up to 100 years ago, and compared them to the genomes of today's individuals. The results are now published at Current Biology.
Many wild animals have declined in number over the past century, and scientists have long been concerned that this decline has resulted in a loss of genetic diversity, increased inbreeding and the accumulation of dangerous mutations. Although this could lead to an even higher risk of extinction in threatened species, investigating recent changes in genetic feasibility has been difficult. In a new study, a team led by scientists from Uppsala University and the Swedish Natural History Museum have used specimens stored in museum collections to analyze changes in the eastern gorilla genome over the past 100 years.
"We found that genetic diversity in Grauer gorillas has decreased significantly in just a few generations," said Tom van der Valk, a PhD student at Uppsala University in Sweden.
Gorilla Grauer was found in the Democratic Republic of the Congo and has declined 80 percent in recent decades due to hunting and habitat destruction. Results from historical and modern genome comparisons show that this decline has led to an increase in blood marriages and loss of genetic variation. This in turn means that Grauer gorillas tend to be less able to adapt to future epidemics and changes in their environment. In addition, scientists have identified several mutations that may be dangerous and which have increased in frequency over the past 4-5 generations as a consequence of decreasing population size. However, in mountain gorillas that are closely related, scientists did not find significant genetic changes, suggesting that their genetic feasibility has remained stable for the past 100 years.
"Recent increases in dangerous mutations strongly emphasize the need to reverse the ongoing decline of the Grauer gorilla population," said Love Dalén at the Swedish Natural History Museum.
Some dangerous mutations that have the potential to increase in frequency are found in genes that affect male disease resistance and fertility. In addition, the researchers identified mutations that caused a loss of function in genes associated with the development of fingers and toes, which might explain why gorillas today sometimes have unified numbers.
"Our study highlights that historical museum specimens are a unique resource for monitoring the latest changes in the genetic status of endangered species," said Katerina Guschanski at Uppsala University.
Interestingly, the reason why Grauer gorillas are more affected than mountain gorillas might lie in their deeper history. While the Grauer gorillas experienced a large increase in numbers between 5,000 and 10,000 years ago, mountain gorillas have been scarce for several thousand years. This long-term small population size may have allowed natural selection to eliminate dangerous mutations before the number of mountain gorillas began to decline in the 20th century.