for National Geographic News
Nearly half of tested captive tigers are "purebred" members of an endangered subspecies, raising the possibility they could bolster conservation efforts, a new genetic analysis suggests.
Similar screening of some of the thousands of tigers with unknown heritage held on farms and by private owners would considerably increase the number of animals useful for captive breeding programs, the scientists say.
The news comes at a dire time for wild tigers. As few as 3,000 individuals remain where more than 100,000 roamed just a century ago. Three of the eight subspecies have become extinct, and a fourth, the South China tiger, persists only in zoos.
(Related: "India's Tigers Number Half as Many as Thought" [August 7, 2007].)
The number of captive tigers, on the other hand, has boomed. Zoos, farms, circuses, and private owners hold an estimated 15,000 to 20,000 tigers. Only a small fraction of these are part of breeding programs oriented toward conservation.
"The captive population of these wild animals has been justified based on the principle that they are the genetic representation of their natural counterparts," said study leader Shu-Jin Luo, who studies genetic variation at the National Cancer Institute in Frederick, Maryland.
"They can act as insurance against extinction in the wild."
Genes Match Geography
But many owners have no knowledge of their cats' ancestry.
To tease apart their heritage, Luo and her colleagues developed a test based on variations in 30 locations on the tiger genome that had originally been identified in domestic cats.
In an earlier study, Luo and her colleagues found that they could separate wild tigers into groups that corresponded to the recognized subspecies based on how many versions of these genetic markers the animals shared.
In the new study, the scientists screened DNA samples from 104 captive tigers living in 14 different countries. Of those, 49 could be confidently assigned to a particular subspecies, they report in Current Biology today.
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