German scientists of the Leibniz Institute for Zoo and Wildlife Research (IZW) and international colleagues have now demonstrated that the Tasmanian tiger, also known as Tasmanian wolf or thylacine, possessed limited genetic variability prior to its extinction. This might have been caused by geographical isolation when Tasmania was isolated from mainland Australia 10-13 thousand years ago.
The Tasmanian tiger, which looks like a wolf but evolved from a marsupial ancestor, has the unfortunate record of being the only species for which we know the exact date and time of its extinction. Despite numerous unconfirmed sightings and searches, no evidence of a living specimen has been found since the last captive animal died at the Tasmanian's Beaumaris Private Zoo in Hobart, Australia on the 7th September 1936.
It is clear that the Tasmanian tiger was practically hunted to extinction due to the imposition of a government bounty from 1888-1909. Yet, one question that has continued to puzzle biologists is how genetically diverse the thylacine population was prior to its extinction. A high level of genetic diversity is very important for populations to effectively adapt to shifting circumstances such as new emerging diseases.
Using a combination of traditional DNA sequencing methods and novel "next generation sequencing technology," a team of international scientists from Germany, the USA and Australia led by Dr Brandon Menzies from the Leibniz Institute for Zoo and Wildlife Research in Berlin and Professor Andrew Pask from the University of Connecticut (USA) demonstrated very limited DNA variability between individual thylacines. These findings were recently published in the journal PLoS ONE. The scientists compared mitochondrial DNA extracted from museum specimens that were 102-159 years old. The Tasmanian tiger specimens were more than 99.5% similar over a segment of DNA normally highly variable between individuals, and when comparing fragments of the whole mitochondrial genome, the sequences were more than 99.9% identical.
Given the recent finding of limited population diversity in the Tasmanian devil (Sarcophilus harrisii), a close living relative of the Tasmanian tiger, these new data suggest that the genetic health of both the devil and the tiger may have been affected by the geographic isolation of Tasmania from mainland Australia approximately 10-13 thousand years ago. Future research should compare the genetic diversity of Tasmania's fauna with populations from the mainland to help protect them from extinction.
The research was supported by an Alexander von Humboldt post-doctoral fellowship to Dr Brandon Menzies.
- Brandon R. Menzies, Marilyn B. Renfree, Thomas Heider, Frieder Mayer, Thomas B. Hildebrandt, Andrew J. Pask. Limited Genetic Diversity Preceded Extinction of the Tasmanian Tiger. PLoS ONE, 2012; 7 (4): e35433 DOI: 10.1371/journal.pone.0035433
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