Many animal populations experience rapid decline due to hunting, logging, agricultural and urban development. However, it remains difficult to directly assess how human activities impact species genetic diversity and with it, the species ability to adapt to environmental changes and ensure long-term species survival. This is because genetic changes usually take many generations to manifest themselves and studying these processes in long-lived animals is challenging.
Figure: The dominant male of one of the Grauer’s gorilla groups in Kahuzi-Biega National Park, eastern DRC, overlooking the activity of his group members during one of the resting breaks. Photo credit: Amy Porter for The Dian Fossey Gorilla Fund.
The critically endangered Grauer’s gorillas that only occur in the eastern Democratic Republic of Congo (DRC)) are the least known of all gorilla species. In the last 20 years, Grauer’s gorillas have suffered a decline of 80% as a direct result of human activities. Several populations, particularly from the periphery of the species distribution, have been lost in the process. What are the genetic effects of such rapid population decline?
To answer this question, we turned to natural history museum collections. As they frequently contain specimens that have been collected centuries ago, they allow us to go back in time, before the most recent, human-driven events took place. We sequenced the complete mitochondrial genomes from 100-year old museum-preserved gorillas and also from fecal samples collected in the DRC in 2014 in collaboration with The Dian Fossey Gorilla Fund International and the Kahuzi-Biega National Park.
This approach allowed us to directly infer how mitochondrial genetic diversity changed in the last century. While the population decline within the core of the Grauer’s gorilla species range did not leave a genetic signal, the loss of peripheral populations resulted in significant decline of the overall mitochondrial diversity. This is because the isolated populations at the edge of the species range harbored a large number of unique mitochondrial variants that are now lost from the species genetic pool. However, conservation efforts frequently focus on the most genetically diverse, large central populations, as these are deemed to have the greatest potential for long-term persistence. Our study highlights peripheral populations as keepers of unique genetic variants and stresses the importance of including them in conservation planning.
Reference
Significant loss of mitochondrial diversity within the last century due to extinction of peripheral populations in eastern gorillas. van der Valk T, Sandoval-Castellanos E, Caillaud D, Ngobobo U, Binyinyi E, Nishuli R, Stoinski T, Gilissen E, Sonet G, Semal P, Kalthoff DC, Dalén L, Guschanski K. 2018. Scientific Reports, 8, 6551