Columbia University environmental scientists confirm in new research that an ancient, two-horned Asian rhinoceros is genetically distinct from its near kin and call for emergency conservation efforts to save it from extinction.
The scientists report in the February 1997 issue of Conservation Biology that DNA studies of the Bornean rhino, a subspecies of Sumatran rhino, clearly distinguish it from other members of its species and indicate a long period of separation and adaptation to its tropical forest habitat on the island of Borneo. Only 50 to 100 of the animals remain. Interbreeding them with other Sumatran rhinos could produce animals ill suited to survive in the wild, the Columbia researchers said.
"If the remaining Bornean rhinos are not brought into an area of sufficient size and habitat quality and protected against poachers, we will lose a unique part of the genetic heritage of this species," said Don J. Melnick, professor of anthropology and biological sciences at Columbia, director of its Center for Environmental Research and Conservation and principal investigator.
More than a million Sumatran rhinos, in evolutionary terms the oldest of all surviving rhino species, roamed across southeast Asia in the mid-19th century. The relatively small and distinctly shaped rhino has fallen prey to human activity: development that has diminished its natural habitat and poachers eager for its twin horns. Even since 1993, when Sumatran rhinos were last counted, the numbers of this elusive mammal have declined dramatically, from fewer than 500 to about 300 animals, including the remaining Borneans and two other populations.
Professor Melnick, an evolutionary geneticist, determined in 1989 that several subspecies of black rhinos in Africa were genetically close enough to allow interbreeding and increase that rhino's chance of survival. That knowledge has helped stabilize the black rhino population at about 2,400 animals.
While interbreeding among subpopulations has helped the black rhino, such a strategy is available only when genetic differences among the populations are slight, Professor Melnick said. The Columbia team found unique mutations and an overall 1 percent difference in the genetic code of the Bornean versus the other Sumatran rhinos, he said, a level considered high enough to avoid interbreeding. Mixing genetically incompatible animals can produce offspring with reduced viability or fertility or hybrids not suited for survival in either parent's environment.
Sumatran rhinos have hairy coats and tufted ears, ancient features that lead biologists to conclude they are among the oldest surviving rhinos. They are small, about eight to nine feet long and three to four feet high at the shoulder, but the Bornean rhino is slightly smaller and its skull is shaped somewhat differently, said Juan Carlos Morales, an associate research scientist at Columbia who performed much of the genetic analysis. Like almost all species, rhinos have been classified by physical characteristics, not genetic differences, and the Bornean rhino has been recognized as a separate subspecies since 1965. Now found only in Sabah state, it has been separated from its Sumatran cousins for at least 10,000 years by water and probably longer by mountains.
Although timber extraction has resulted in loss of rhino habitat on Borneo, poachers have taken a far greater toll. Poachers seek rhino horns for ornamental dagger handles and purported medicinal benefits. Black market prices of as much as $100,000 for a single horn have spurred them to shoot rhinos of all ages and sizes.
The Columbia study will be a valuable tool for government conservation officials in Malaysia and Indonesia, said Thomas Foose, program officer for the International Rhinoceros Foundation in Cumberland, Ohio, which is working with local governments to preserve rhinoceros populations around the world. The study provides a detailed map of the Sumatran rhino's genetic diversity, information that could not have been provided without genetic analysis techniques developed over the last decade, Professor Melnick said.
Co-authors of the research with Drs. Melnick and Morales of Columbia were Patrick Mahedi Andau, director of the Wildlife Department of Sabah state; Jatna Supriatna, professor of biology at the University of Indonesia, Depok; and Zainal- Zahari Zainuddin, chief wildlife veterinarian at the Wildlife Department of peninsular Malaysia's Zoo Melaka.
In 1992, Columbia scientists began working with conservation officials in Indonesia and Malaysia to collect genetic specimens - blood or hair - from wildborn Sumatran rhinos, some in zoos. The study eventually included animals from four populations: peninsular Malaysia, Sabah in Borneo, Riau in eastern Sumatra and Bengkulu in western Sumatra. Researchers examined the DNA in cell bodies called mitochondria, because such DNA evolves relatively rapidly, making it a good indicator of recent genetic changes. They used enzymes that cleave the animals' DNA at specific sequences of base pairs, then compared the resulting fragments for genetic similarity.
The scientists found no genetic differences between the samples from peninsular Malaysia and eastern Sumatra, slight differences between the eastern and western Sumatran populations, and larger differences between the Bornean rhino and the other populations. The findings indicate the Bornean rhino has been separated from the other subpopulations for a longer period of time, Professor Melnick said, allowing the development of genetic distinctions, which are probably both adaptations to local conditions and neutral mutations.
The Wildlife Department of Sabah state is undertaking an effort to preserve the Bornean rhino by creating a breeding sanctuary in Sepilok, with assistance from the rhino foundation and the Asian Rhino Specialist Group of the World Conservation Union, Dr. Foose said. Since efforts to breed the Sumatran rhino in captivity have been unsuccessful, local governments are creating natural sanctuaries at three sites, which also include Way Kambas National Park in Sumatra and Sungai Dusun in peninsular Malaysia.
Under a grant from the Global Environmental Facility of the United Nations Development Program, the rhino conservation groups have also coordinated training and deployment of antipoaching teams and rhino conservation officers in about a dozen locations in both countries, Dr. Foose said.