DNA from an extinct sub-species of tiger has revealed that the ancestors of modern tigers migrated through the heart of China – along what would later become known as ‘the Silk Road’ – a team of scientists from Oxford University and the NCI Laboratory of Genomic Diversity in the USA report.
In a study recently published in PLoS One the team show that the Caspian tiger from Central Asia, which became extinct in 1970, was almost identical to the living Siberian, or Amur, tigers found in the Russian Far East today.
The discovery not only sheds new light on how the animals reached Central Asia and Russia but also opens up the intriguing possibility that conservationists might repopulate tiger-less Central Asia with Siberian tigers from Russia or China.
‘What these striking results indicate is that extinct Caspian tigers and modern Siberian tigers are molecular nearest neighbours,’ said Carlos Driscoll, a doctoral student studying at Oxford University’s Wildlife Research Conservation Unit (the WildCRU) who led the study. ‘In a sense it means that Caspian tigers never became extinct, it’s just that there never was any such thing as a ‘Siberian’ tiger.’ The relationship is so close that the mitochondrial DNA of the two sub-species differs by just a single nucleotide.
Because Caspian tigers were not well studied before they became extinct almost 40 years ago the team had to retrieve DNA from specimens held in the region’s museums.
‘We had to travel through Russia and Central Asia taking tiny bone samples from Caspian tiger specimens in natural history collections,’ said co-author Dr Nobby Yamaguchi of Oxford’s WildCRU. ‘We then compared the mitochondrial DNA from these samples with those taken from living animals, especially Siberian and Indian tigers.’
The route that Caspian tigers took to get to Central Asia has always been a puzzle because Central Asian tigers seemed isolated from other populations by the massive Tibetan plateau. The new research suggests that rather than skirting around the plateau, via India to the south or Siberia to the north, perhaps about 10,000 years ago ancient tigers went through it along China’s narrow Gansu Corridor – which would thousands of years later form part of ‘the Silk Road’ trading route.
This fresh look at the tiger family tree suggests that the South China tiger, a sub-species now extinct in the wild, is unique – possibly the cat most closely resembling the ancestor of all modern tigers – making efforts to save it from extinction all the more important.
‘We came very close to losing the chance to study the South China tiger, even from a molecular standpoint, simply because it is so rare,’ commented Carlos Driscoll. ‘Hopefully our findings will encourage the Chinese government to focus conservation efforts on this most endangered of living tigers.’
Professor David Macdonald, Director of the WildCRU at Oxford University and also one of the authors said: ‘The fact that the Caspian tiger was driven extinct in 1970 is an indictment of the modern age and not some long-gone piece of history. Our research indicates that the Caspian tiger’s genes still exist, in the form of the Siberian tiger, so they could be restored to Central Asia. This restoration would obviously be a huge undertaking but what a triumph it would be!’
- Carlos A. Driscoll et al. Mitochondrial Phylogeography Illuminates the Origin of the Extinct Caspian Tiger and Its Relationship to the Amur Tiger. PLoS One, Jan 14, 2009 [link]
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