Gould’s mouse was declared extinct, but DNA shows it still lives on an island in Shark Bay, Western Australia – ABC News

Before European settlers set foot on Australian shores, Gould's mouse scurried about thecontinent.

Butland clearing and the introduction of predatorsdecimated native rodent populations, and the little mouse was declared extinct more than a century ago until now.

A team of researchers, led by Emily Roycroft of the Australian National University, looked at genomes of Australia's extinct and living rodents.

Their analysis showsa small population ofGould's mouse (Pseudomys gouldii) lives on an islandoff the coast ofWestern Australia.

But thislittle animal with shaggy fur and large black eyes is knownby another name.

Gould's mouse isactually the samespecies as the Shark Bay mouse (Pseudomys fieldi), they reporttoday in the journalProceedings of the National Academy of Sciences.

"I was quite surprised," Dr Roycroft said.

"Extinction doesn't usually offer second chances."

Australia is home to some of the world's most unique wildlife, with 86per cent of its mammals notfound anywhere else.

But it hasalso lost more mammals over the past 200 years than any other country, with 34 land species being declared extinct since Europeans set foot on the continent in 1788.

Native rodents make up nearly half of these extinctions.

Wikimedia Commons: John Gould

Their rapid decline was likely due to a mix of human impacts.

Along with land clearing and introducing predators such as cats and foxes, early settlers were also keen bounty hunters.

"Basically, the government paid people to bring in dead animals," she said.

And while Gould's mouse was once widespread, it was one of the hardest hit speciesduring European colonisation and hasn't been seen on the mainland since 1895.

But what hasn't been clear is whether Australia's rodents were already struggling before the first settlers arrived.

Dr Roycroft and her colleagues wanted to look at this group's genetic diversitybefore its numbers took a nosedive nearly 200 years ago.

Conservationists often use a population's genetic diversity as a measure of resilience against stressors such as disease and environmental change.

Having a large mix genes gives a species a better chance of adapting to its changing environment.

To assess the genetic diversity of Australia's rodents prior to European settlement, the researchers extracted DNA fromeight extinct rodent species and 42 of their living relatives from museum specimens.

The specimens had been collected between 120 and 184 years ago.

Supplied: C.Ching, Courtesy of the Trustees of the Natural History Museum, London

In the Museums VictoriaAncient DNA Laboratory, the researchers sequenced the specimens' genomes to look at how they're related and how their genetic makeup had changed over time.

They found that the rodents' genomes were diverse before European settlement, indicating that their once-thriving populations were more likely wiped out by human impacts than genetic weakness, such as inbreeding.

The rodents' healthy genomes suggested they declined rapidly, unlike other extinct mammals such as the Tasmanian tiger.

The team also found that larger species were more likely to become extinct.

This is because larger rodents tend to be more attractive to predators and produce fewer young than their smaller relatives.

But there was one extinct species that stood out.

When the researchers analysed the genome of the Gould's mouse specimen, they found that it matched up with a species currently living on the islandsoff Shark Bay in Western Australia.

This means the mousenever completely died out to begin with.

This came as a surprise, as Gould's mouse specimens were originally collected in New South Wales and Victoria over 4,000 kilometres away from Shark Bay.

"That's a really big distance,so I was surprised that those things were essentially the same species," Dr Roycroft said.

"But this has revealed that it was in fact a once very widespread single species that had collapsed down into this single off-shore population."

But how did these mice get there in the first place?

Dr Roycroft said they likely made their way over when the islands were still connected to the mainland thousands of years ago.

"Slowly as the sea level rose, a little pocket of the population may have got trapped there," she said.

Euan Ritchie, a wildlife ecologist at Deakin University, said that it's "fantastic news" that Gould's mouse is aliveon an island in Shark Bay.

But becausethe species is listed as endangered, it's important to make it a conservation priority, said Dr Ritchie, who was not involved in the study.

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"Given this species occurs in such an isolated and single location, establishing captive breeding colonies and additional wild populations should be a priority," he said.

Dr Ritchie also said the study highlightedthe need for more investment in surveying, cataloguing and describing Australia's wildlife.

"We risk being unaware of the true diversity of Australia's species, and hence unable to care for and conserve it properly," he said.

"We essentially risk losing what we don't even know exists."

The next step for Dr Roycroft and her teamis to analyse the genomes of other native animals to look at how they were also impacted by European settlers.

"I hope this study can be an inspiration to looking at other species and seeing what we can learn about Australia's biodiversity that we've lost," Dr Roycroft said.

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Gould's mouse was declared extinct, but DNA shows it still lives on an island in Shark Bay, Western Australia - ABC News