A new study led by University of Adelaide researcher Jeremy Austin traces the history of Tasmanian tiger (thylacine) populations over the last 30,000 years.

The thylacine (Thylacinus cynocephalus) was a carnivorous marsupial about the size and shape of a medium-to-large size dog, but had tiger-like stripes running down its lower back and an abdominal pouch. It is one of only a few marsupials to have a pouch in both sexes.

“Thylacines once lived across most of the Australian mainland, but by the time Europeans arrived in the late 1700s they were found only in Tasmania,” Dr. Austin said.

“They became extinct about 150 years later, with the last of the species dying in Hobart Zoo in 1936.”

“But the reasons for their disappearance from mainland Australia and continuing survival in Tasmania has remained a mystery. Climate change, increased human activity and the introduction of the dingo are the three main causes debated.”

Dr. Austin and his colleagues from the University of Adelaide’s Australian Centre for Ancient DNA generated 51 thylacine mitrochondrial DNA (mtDNA) genome sequences from fossil bones and museum specimens — the largest dataset of thylacine DNA to date.

“We wanted to understand why thylacines went extinct on the mainland, but survived in Tasmania,” said PhD student Lauren White, first author of the study.

The team found genetic evidence that mainland thylacines had contracted into separate eastern and western populations in southern Australia before the last Ice Age peak (25,000 years ago), and that the ancient western population was larger and more genetically diverse than the historical Tasmanian population.

“A large and genetically diverse population of thylacines lived in western regions of Australia right up to their extinction from the mainland around 3,000 years ago, separated from the eastern population,” the scientists explained.

“The ancient mtDNA tells us that the mainland extinction was rapid, and not the result of intrinsic factors such as inbreeding or loss of genetic diversity,” Dr. Austin said.

“Climate change from about 4,000 years ago, in particular more drought-prone seasons caused by the onset of the El Niño-Southern Oscillation (ENSO), was the likely main cause.”

“We also found evidence of a population crash, reducing numbers and genetic diversity of thylacines in Tasmania around the same time.”

“At the time of European arrival, Tasmanian thylacines had limited mtDNA diversity, possibly resulting from a bottleneck event broadly coincident with an ENSO-associated climate event,” the researchers said.

The findings are published in the Journal of Biogeography.

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Lauren C. White et al. Ancient mitochondrial genomes reveal the demographic history and phylogeography of the extinct, enigmatic thylacine (Thylacinus cynocephalus). Journal of Biogeography, published online September 27, 2017; doi: 10.1111/jbi.13101