Scientists confirm limited genetic diversity in the extinct Tasmanian tiger

The results published April 18 in the international journal PLoS One, provide insights into the genetic health of the thylacine (Thylacinus cynocephalus) before it was exterminated by hunting.

Lead author Dr Brandon Menzies, an Honorary Fellow of the University of Melbourne, who completed the study at the Leibniz Institute for Zoo and Wildlife Research in Berlin, said the latest study revealed that the Tasmanian Tiger had the same or even less genetic diversity than its close relative the Devil.

"Hence, Tasmanian Tigers may have faced similar environmental problems to the Devils, had they survived," Dr Menzies said.

"Due to the similarly poor genetic diversity of the animals, this new data suggests that the genetic health of the Tasmanian Tiger and Devil may have been affected by the geographic isolation of Tasmania from mainland Australia approximately 10-13 thousand years ago," he said.

The thylacine has been the focus for biologists due to its unique evolution in Australia and extinction. Having evolved from a marsupial into a mammal that is very similar to a dog or wolf, but being marsupials, the females had a pouch in which they carried their young.

Dr Menzies said that while the thylacine was hunted to extinction due to the imposition of a government bounty from 1888-1909, with the last known animal dying in captivity in 1936, one question that continued to puzzle biologists was how genetically diverse the thylacine population was prior to its extinction.

Using a combination of traditional DNA sequencing methods and next generation sequencing technology, a team of international scientists led by Dr Brandon Menzies, and Dr Andrew Pask, from the University of Connecticut, who also holds a fractional appointment at the University of Melbourne's Zoology Department, demonstrated the very limited DNA variability between individual thylacine specimens.

With contributions from scientists in Germany, the USA and Australia, researchers compared mitochondrial DNA extracted from 14 museum specimens that were between 102-159 years old.

The results revealed the thylacine specimens were more than 99.5 per cent similar over a portion of DNA that is normally highly variable between individual animals.

"If we compare this same section of DNA, the Tasmanian Tiger only averages one DNA difference between individuals, whereas the dog, for example has about 5-6 differences between individuals," Dr Menzies said.

He said in a direct comparison with other species, the thylacine averages about 5-10 DNA base differences over the coding sections of the mitochondrial genome.

"This is quite low when compared to other species including the wolf (77) or African humans (85). The Tasmanian Devil has about 10 DNA differences between individuals over the whole genome, which is also low.'

"This work highlights our need to understand all of Tasmania's and Australia's unique flora and fauna so they are also not lost to extinction," he said.

University of Melbourne co author Professor Marilyn Renfree from the Department of Zoology who collected some of the DNA samples from specimens held in the Museum Victoria, said this work builds on her previous work in 2008 with Dr Pask, and Professor Richard Behringer from the University of Texas, on resurrecting a gene from the Tasmanian Tiger in a mouse, and confirms a previous study on two thylacine individuals.

"This new study confirms the relatively low genetic diversity in the Tasmanian Tiger which sadly was hunted to extinction. We cannot bring the Tiger back to life, but at least we can continue to learn as much as possible about these iconic marsupial carnivores."

The research was supported by an Alexander von Humboldt post-doctoral fellowship to Dr Brandon Menzies and the Leibniz Institute for Zoo and Wildlife Research in Berlin.