When a population rapidly plummets, the chance sampling of genetic drift and inevitable inbreeding can accelerate the pace of extinction. A new report in Current Biology reveals the genetic evidence behind the dire situation for Grauer’s gorilla.
Ancestral gorillas split into eastern and western species about 150,000 years ago. The western animals then split to yield the western lowland gorilla and the cross river gorilla subspecies. The eastern contingent diverged to give rise to the mountain gorilla and Grauer’s gorilla (aka eastern lowland) subspecies. This last primate lives in the Democratic Republic of Congo and is critically endangered.
From 5 to 10 million years ago, eastern gorillas were doing just fine. Then about 100,000 years ago, their populations began to decline. About 10,000 years ago they split into the mountain and Grauer’s subspecies. Then from 5,000 to 10,000 years ago, the Grauer’s population took off, expanding so quickly that some dangerous mutations occurred and accrued. Mountain gorilla populations remained fairly small, the numbers not allowing many mutations to accumulate.
Then about twenty years ago, the Grauer’s group hit a population bottleneck, and the numbers crashed down to about 4,000 animals, thanks to habitat destruction and poaching.
To continue reading go to my blog DNA Science, at Public Library of Science, where this article first appeared.