Much of the continent is in the middle of a mouse plague of epic proportions, but there is one rodent Australian scientists are delighted to see alive. Gould's mouse (Pseudomys gouldii) was thought to have been extinct for around 150 years, but genetic analysis published in the Proceedings of the National Academies of Science shows it's still hanging on – albeit only on some small islands.
Although most of Australia's mammals are marsupials, rodents reached there six million years ago and carved out numerous niches without displacing many pouch-bearers. Recently, however, they have suffered even more heavily than the marsupials at the hands (and paws) of new arrivals, contributing to Australia's status as the world's worst site for mammal extinction.
Dr Emily Roycroft of the Australian National University was investigating the genetics of extinct native rodents when she hit on something quite unexpected. Museum specimens of Gould's mouse, collected in 1839 and thought to have gone extinct soon after, are actually the same species as the surviving Shark Bay mouse (P. fieldi), also known as the Djoongari.
"The resurrection of this species brings good news in the face of the disproportionally high rate of native rodent extinction, making up 41 per cent of Australian mammal extinction since European colonization in 1788," Roycroft said in a statement.
The Djoongari was once widespread across Western Australia and also found in the east. At one point it was reduced to a single island, but the Wildlife Conservancy has established reserve populations on several other islands off Western Australia in case of disaster. Roycroft told IFLScience the new populations are flourishing, but the mouses' lack of genetic diversity remains a threat to its survival.
Roycroft told IFLSceince that the project began with exploring genetic diversity from a different angle, among museum specimens of eight species collected in their last days. “We wanted to see if they collapsed to extinction directly as a result of European colonization or were already in decline,” she said. Roycroft attributes the idea many extinct species were in trouble before Europeans arrived to evidence from the thylacine, which had been wiped out on the mainland from competition with the dingo, and was genetically depleted in Tasmania.
However, Roycroft found, the same was not true for the native rodents, which were flourishing.
The paper reports the arrival of Europeans and their animals hit the larger rodents harder. Although the reasons for this are uncertain, Roycroft thinks feral cats and foxes may have preferentially targeted larger mice.
Although introduced species and habitat destruction were the main reasons for the native rodents' decline, many were killed deliberately as part of a bounty program. Roycroft says it is possible that had humans not deliberately driven so many to destruction, the natives might have prevented the house mouse from achieving the same dominance. Although its plagues could not have been prevented entirely, disasters like the one currently hitting the grain growers might have been mitigated, were it not for these historical mistakes.