Washington, April 18 : A new report has determined that many captive tigers held in captivity around the world represent purebred subspecies and harbor genomic diversity no longer found in nature, which may raise their conservation value.
The report, published online in Current Biology, used a new method for assessing the genetic ancestry of tigers.
Tigers in general are disappearing rapidly from the wild, from over 100,000 in the 1900s to as few as 3,000 last year.
By contrast, captive tigers are flourishing, with 15,000-20,000 individuals worldwide, outnumbering their wild relatives between five and seven to one.
According to Shu-Jin Luo, of the National Cancer Institute, Frederick, US, "Assessment of 'verified subspecies ancestry' (VSA) offers a powerful tool that, if applied to tigers of uncertain background, may considerably increase the number of purebred tigers suitable for conservation management."
"This approach would be of particular importance to tiger subspecies that have suffered severe population decline in the wild and/or lack of efficient captive breeding," said Luo.
For example, the Indo-Chinese tiger has been classified as a different subspecies from the Malayan tiger, leaving just 14 recognized Indo-Chinese individuals in captivity.
"Thus, verification of VSA Indochinese tigers, establishment of captive breeding programs, and preservation of remaining Indochinese tiger populations in the wild should be set as one of the top priorities in the global tiger conservation strategy," said Luo.
A relatively small portion of the world's captive tigers-some 1,000 individuals in all-are managed through coordinated breeding programs that aim to preserve genetic variability representative of geographic and subspecies groupings found in the wild.
The rest are of hybrid or unknown origin and are kept in zoos, farms, breeding facilities, circuses, and private homes.
Scientists have long debated the role that captive tigers might play in conservation efforts.
To address the issue in the new study, the researchers developed a strategy for assessing the subspecies affiliation of tigers on the basis of diagnostic genetic markers obtained from 134 "voucher" tigers.
They applied the method to samples from 105 captive tigers from 14 countries collected over 20 years. Of those, 49 individuals were found to represent one of five purebred subspecies, or VSA. The rest of the tigers had mixed backgrounds.
According to the researchers, if 14-23 percent of the over 15,000 existing captive tigers would prove to be VSA, the number of tigers with pure subspecies heritage available for conservation consideration would considerably increase.