By Joseph Milton
Orangutans can now be added to the list of species that have had their genomes sequenced, offering conservationists a wealth of data in their efforts to save the endangered great ape.
A group of researchers in the United States and Europe has published a draft of the genome of a captive orangutan called Susie, and less complete copies from ten wild individuals.
"We've developed a resource that could allow conservationists to prioritize populations for saving based on genetic diversity," says Devin Locke at the Genome Center at Washington University in St Louis, Mo., who led the study. "Zoo breeding programs could also be informed by genetics, allowing them to maintain maximum diversity."
But whether genetic data can really help to conserve orangutan populations in the wild remains unclear. The apes are native to Sumatra and Borneo, where they are under intense pressure as their tropical forest habitats are destroyed to grow oil-palm plantations and for logging and mining.
"Saving orangutans is more about commerce and politics than genetics," says Andrew Balmford, a conservation scientist at the University of Cambridge, UK. "The rate of decline is so severe that we've only got another 20 or 30 years before the game's up."
Analyzing the DNA of the 10 wild great apes, five from Borneo and five from Sumatra, the team found that genetic diversity was lower in Bornean orangutans (Pongo pygmaeus) than in their Sumatran relatives (Pongo abelii). Because Borneo is home to six or seven times as many orangutans as Sumatra, this might seem counter-intuitive.
But William Amos, an evolutionary geneticist at the University of Cambridge, says it is not that surprising. "We don't fully understand the relationship between genetic diversity and population size," he adds.
Amos says that genetic diversity is not necessarily a clear indicator of the viability of populations anyway. "Nobody has done really convincing experiments to show that diversity is important," he explains. "High diversity may actually mean a species is facing lots of diseases and has to maintain lots of different immune-system alleles, so it could in fact be more vulnerable."
However, Locke says the consortium is not presenting the data, published January 26 in Nature, as a basis for making conservation-management decisions. "The database we developed can be used to generate a tool for genetically profiling orangutan individuals and populations," he says. "It's the profiling data that would be useful in making management decisions."
And he is convinced of the link between genetic variability and population viability. "Studies have shown a statistical correlation between the loss of genetic diversity and an increase in extinction risk in other species," he says.
By comparing the DNA of the Bornean and Sumatran orangutans, the researchers estimate that the two species diverged around 400,000 years ago, more recently than was previously thought.
The researchers also compared their orangutan data with chimpanzee and human DNA, and were surprised to find that the orangutan genome has evolved much more slowly than either species.
Locke suggests that this could be because the orangutan genome contains far fewer mobile DNA elements, which he says may act as "a kind of lubricant", facilitating rearrangements of DNA.
Even if the orangutan genetic data cannot help to save the great apes, they may prove useful in furthering the understanding of human genetic disease. The researchers identified a set of actively evolving genes in orangutans that are associated with metabolic pathways involved in neurodegenerative conditions in humans.
"Orangutans also develop cardiovascular disease and spontaneous diabetes like humans," says Oliver Ryder, a biologist at San Diego Zoo's Institute for Conservation Research in Escondido, California, who also worked on the study. He says the orangutan genome might help in developing treatments for such conditions by allowing in-depth analysis of the diseases' evolution in great apes.