One possible clue to the lack of structural rearrangement in orangutan DNA is a profound lack of repetitive "Alu" elements. These short stretches of DNA make up about 10 percent of the human genome and can pop up in unexpected places to create new mutations or genetic rearrangements.
The human genome possesses about 5,000 human-specific Alus, while the chimp has about 2,000 chimp-specific Alus.
"In the orangutan genome, we found only 250 new Alu copies over a 15 million-year time span," Locke says. "This is the closest thing we have to a smoking gun that may explain the structural stability in the orangutan genome."
The initial Sumatran orangutan genome was sequenced using legacy technology and cost $20 million to complete. Using more sophisticated technology, the cost of sequencing the additional orangutans dropped substantially to about $20,000 each. The project was funded by the National Human Genome Research Institute, the National Science Foundation and other organizations.
The new research shows that the Sumatran and Bornean orangutans diverged some 400,000 years ago. Earlier estimates had put the split at about 1 million years ago. Today, only about 50,000 Bornean and 7,000 Sumatran orangutans still live in the wild.
But in a finding that seems counterintuitive, the researchers found the smaller population of Sumatran orangutans is genetically more diverse than their Bornean cousins.
"It's quite a mystery how Sumatran orangutans obtained this genetic diversity or whether there has been cleansing of diversity in the Borneans," Locke explains. "We can begin to search for answers using the catalog of genetic variation we developed."
Studies of orangutans are important because these great apes, in particular, are under intense ecological pressure. Their numbers continue to erode as humans encroach further on their habitat.
"Orangutans spend more than 95 percent of their time in the trees," Locke says. "They travel through the trees, nest in trees and forage for food in trees. But all the genetic diversity in the world can't save them in the wild if their habitat is destroyed."
Researchers led by Washington University in St. Louis have decoded the DNA of 11 orangutans. An analysis of their genomes reveals intriguing clues about the evolution of great apes, including humans, and showcases the immense genetic diversity across and within Sumatran and Bornean orangutans, which are endangered in the wild.
(Photo Credit: Washington University in St. Louis)
In the Malay language, orang-utan means "man of the forest." Washington University scientists led an international project to sequence the orangutan genome. The work is expected to aid conservation efforts and the study of human evolution.
(Photo Credit: Perry van Duijnhoven/Carel van Schaik)