Efforts to save the endangered Sumatran rhinoceros should focus on preserving a subspecies in Borneo, says a team of American, Indonesian, and Malaysian researchers. The scientists report in next month's issue of Conservation Biology that the genes of the Bornean rhino differ significantly from those of other southeast Asian populations.
The Sumatran rhino may be the closest to extinction of the five rhino species, says team leader Don Melnick, a geneticist at Columbia University. The nocturnal creatures with their hairy skin and tufted ears live deep in forests, but have been hunted relentlessly for their horns. Since the mid-19th century, the population has plummeted from an estimated 1 million to about 300, including 50 to 100 Bornean rhinos that are thought to remain in the wild.
To help conservationists develop the best plan for managing the surviving Sumatran rhinos, Melnick and his colleagues mapped the species' genetic diversity. "If the aim is to maximize diversity, you need to know how it's distributed on the landscape," says Melnick. His team collected blood and hair samples from captive rhinos that were born wild in Malaysia and on the islands of Sumatra and Borneo. Mitochondrial DNA in these rhinos has evolved rapidly enough to reveal mutations that have accumulated since the Bornean population was sundered by a sea-level rise several thousand years ago from rhinos to the east on Sumatra and the Malaysian peninsula.
The team discovered that Bornean rhinos varied from these populations by 1% of their mitochondrial DNA. "That's a big difference, especially for large animals," says Melnick. He is now looking for similar changes in DNA in the cell nucleus, which contains most of the genes critical for a species' survival.
Although the study is interesting, says Eric Dinerstein, a biologist with the World Wildlife Fund in Washington, D.C., he argues that information about the ecological roles of subspecies may be an even more important criterion than genetic makeup in designing conservation strategies.
Although the Bornean rhino population is on the brink, it could still rebound on its own, Melnick says, but only if it's protected from its number-one enemy: poachers.