Tigers are in trouble worldwide; there are only about 3,000 remaining in the wild, down from about 100,000 a century ago. There are 15,000 to 20,000 tigers in zoos, breeding facilities, circuses and even private homes. Only about 1,000 of these animals are in managed breeding programs that are designed to preserve genetic diversity among Bengal, Sumatran and other tiger subspecies. As for the other captive tigers, they are considered “generic” — their genetic makeup is either unknown or they are considered hybrids.

But a new study in Current Biology suggests that these tigers are not so generic after all. Shu-Jin Luo and Stephen J. O’Brien of the Laboratory of Genomic Diversity at the National Cancer Institute and colleagues report that perhaps 20 percent of these captive tigers are purebred and retain genetic variations that are not found in the wild.

The researchers performed genetic analyses of DNA samples from 105 captive tigers of uncertain pedigree, and compared the results with data from an earlier analysis of 134 tigers of known genetic distinctiveness. They found that 49 of the 105 captive tigers, or about 47 percent, could be categorized as being of one of five subspecies.

Since some of the 49 were from breeding programs, the researchers suggest that the percentage of purebreds in the full captive population is probably lower, about 14 percent to 23 percent. Still, that represents a new pool of genetically distinct tigers potentially available for breeding efforts.

(By HENRY FOUNTAIN, NYT, 29/04/2008)