A species of mouse that was presumed extinct for more than 150 years has been discovered alive on a remote offshore island, enabling scientists to “taxonomically resurrect” it, according to a new study.
Gould’s mouse (Pseudomys gouldii), a small rodent with shaggy fur, once roamed across a huge swath of Australia, but its population catastrophically crashed by the 1840s, shortly after the arrival of Europeans on the continent. Sadly, its sudden decline mirrors a larger pattern of human-driven mass extinction in Australia over the past 200 years, which has been particularly devastating for rodents. As a result, Gould’s mouse was written off as one of the many animals wiped out by the arrival of Europeans.
Researchers led by Emily Roycroft, an evolutionary biologist and postdoctoral research fellow at the Australian National University, published unprecedented new research into this sudden “extinction vortex” on the continent, which has sucked countless rodents into oblivion, on Monday in the Proceedings of the National Academy of Sciences.
The overall results of the study are extremely concerning, but the team was fortunately able to determine that Gould’s mouse has managed to survive in small populations off the coast of Shark Bay in Western Australia, where it is known as the Shark Bay mouse (Pseudomys fieldi), or the djoongari.
“When we started the study, we weren’t expecting to find that Gould’s mouse and the Shark Bay mouse were the same species,” Roycroft said in an email. “The result initially came as a surprise, especially given how geographically separated the records of Gould’s mouse (in Victoria/New South Wales) are from the Shark Bay mouse (isolated on an island off the coast of Western Australia).”
Roycroft and her colleagues were able to show that the two mice are the same species thanks to their extensive genetic analysis of rodent specimens in museum collections. In a first-of-its-kind approach for Australian rodents, the team sequenced genes from 85 specimens representing 50 species that date back 184 years.
The size of the sample, both in terms of species and timescales, enabled the researchers to reconstruct important details about the collapse of rodent populations, which account for 41 percent of all mammal extinctions in Australia.
“It's hard to know for sure how species are related to each other unless we have genetic data,” Roycroft said. “In our study, we used genetic data to determine species relationships, and were then able to control for this in our correlations.”
For example, the team confirmed that larger-bodied rodents are more likely to experience decline or go extinct, and that extinction occurs more frequently in arid and mesic habitats. In addition to teasing out these correlations, the study yielded insights into the timeline of rodent extinction on the continent.
For instance, some animals, such as the extinct Australian thylacine (a marsupial predator), may have been in decline on the mainland before the 18th century, though the arrival of Europeans hastened their demise.
However, the study reveals that Australian rodents were flourishing prior to European colonization, judging by their past abundance, genetic diversity, and range. The sudden disappearance of the rodents is clearly linked with anthropogenic pressures from recent changes, which include “predation by feral cats and foxes, competition with introduced rodents, anthropogenic environmental disturbance, habitat destruction by introduced herbivores, inappropriate fire management, the introduction of novel diseases, and climate change,” according to the study.
“The loss of so many species of native rodents means a loss of integral parts of Australian ecosystems,” Roycroft said. “Native rodents feed on many plants, fungi, and invertebrates, and in turn are a source of prey for many native carnivores. In the absence of native rodents, entire Australian ecosystems are potentially at risk of collapse.”
The resurrection of Gould’s mouse does provide some good news, but even that silver lining borders a dark cloud. This species was clearly driven to the predator-free island that it now inhabits by the same human-driven changes that have wiped out so many of its rodent relatives. As a result, the species retains only a fraction of its genetic diversity and could still become extinct without targeted conservation funding, including efforts to translocate it to other predator-free sites in Australia.
Roycroft and her colleagues hope their research will lead to other genomic assessments of wildlife declines in Australia, which has the highest historically recorded rate of mammalian extinction in the world.
“Our study shows just how much we can learn about the species we’ve otherwise lost to extinction, using genomic data from museum specimens,” she said. “If we can generate this type of data from across all of Australia’s native species, not just rodents, we can learn more about the broader pattern and pace of extinctions. This will allow us to fully take stock of what we’ve already lost to extinction, but also help inform conservation efforts for surviving species into the future.”