Many tigers held in captivity have "pure-bred ancestry" and could play a key role in the survival of diminishing wild populations, a study suggests.

A team using a new method for assessing the genetic ancestry of tigers found that a number of "generic" animals were actually pure-bred subspecies.

Writing in Current Biology, they added that these tigers also had genomic diversity no longer found in the wild.

Current estimates suggest that only about 3,000 tigers remain in the wild.

In contrast, the international team of researchers noted, the global population of captive tigers numbered between 15,000 to 20,000.

But they highlighted that only about 1,000 of these were managed within co-ordinated breeding programmes that aimed to preserve the animals' genetic variability.

They wrote: "As of 2007, there are approximately 421 Amur, 295 Sumatran, 72 South China, 198 Bengal, 14 Indochinese and 113 Malayan tigers in captivity as recorded in regional and international zoo studbooks.

"Debates persist over the role of captive tigers in conservation efforts, whether managed captive populations serve as adequate genetic reservoirs for the natural populations, and whether the generic tigers have conservation value," they observed.

"The most direct way to address the dilemma is through a thorough understanding of the genetic ancestry... and the level of genetic diversity of captive tigers relative to wild populations."

Conservation boost

By analysing 20 years' worth of DNA samples from 105 captive tigers, and using data from tigers with known ancestry as a reference, the team was able to identify genetic patterns that would suggest a match with one of the pure-bred subspecies.

"Assessment of 'verified subspecies ancestry' (VSA) offers a powerful tool," explained co-author Dr Shu-Jin Luo, from the US National Cancer Institute.

"If applied to tigers of uncertain background, it may considerably increase the number of pure-bred tigers suitable for conservation management," she added.

Of the 105 animals studied, the researchers identified 49 individuals that belonged to one of the pure-bred subspecies.

However, they suspected that the study overestimated the proportion of pure-breds in the captive population because 43 of the tigers tested were already enrolled in established breeding programmes.

But they added that 14 of the 62 un-enrolled animals were deemed VSA: "If [up to 23%] of the 15,000 existing captive tigers would prove to be VSA, the number of tigers with pure subspecies heritage available for conservation would considerably increase.

"Also, an important fraction of captive tigers retain genetic diversity unreported, and perhaps absent, in the wild populations.

The team concluded that their findings suggested that a comprehensive programme to identify captive VSA tigers could help secure the long-term survival of the wild population.

"Their potential for inclusion into comprehensive, integrated in-situ and ex-situ management plans could significantly increase population sizes and help maintain genetic variability and population viability of this iconoclastic species."

(BBC)

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