Extract from ABC News
Before European settlers set foot on Australian shores, Gould's mouse scurried about the continent.
But land clearing and the introduction of predators decimated native rodent populations, and the little mouse was declared extinct more than a century ago – until now.
Key points:
- Australia has the highest mammal extinction rate in the world
- Gould's mouse was thought to be extinct, but it is actually alive on an island off Western Australia, where it is known as the Shark Bay mouse
- Scientists say the species should be a conservation priority to ensure the last population doesn't die out
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 shows a small population of Gould's mouse (Pseudomys gouldii) lives on an island off the coast of Western Australia.
But this little animal with shaggy fur and large black eyes is known by another name.
Gould's mouse is actually the same species as the Shark Bay mouse (Pseudomys fieldi), they report today in the journal Proceedings of the National Academy of Sciences.
"I was quite surprised," Dr Roycroft said.
A rapid disappearance
Australia is home to some of the world's most unique wildlife, with 86 per cent of its mammals not found anywhere else.
But it has also 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.
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 species during European colonisation and hasn't been seen on the mainland since 1895.
Tracking extinction in the genes
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 diversity before 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 from eight extinct rodent species and 42 of their living relatives from museum specimens.
The specimens had been collected between 120 and 184 years ago.
In the Museums Victoria Ancient 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.
Resurrecting an extinct mouse
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 islands off Shark Bay in Western Australia.
This means the mouse never 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 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.
Second chances should not be wasted
Euan Ritchie, a wildlife ecologist at Deakin University, said that it's "fantastic news" that Gould's mouse is alive on an island in Shark Bay.
But because the species is listed as endangered, it's important to make it a conservation priority, said Dr Ritchie, who was not involved in the study.
"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 highlighted the 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.
The next step for Dr Roycroft and her team is 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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