Shark Bay is a lonely island off the coast of Australia, where sienna-streaked cliffs meet the sea and ancient, bulbous stromatolites dot the landscape. This natural wonderland is not just a UNESCO world heritage site, but it also happens to be one of the few remaining homes for the elusive Gould’s mouse, an Australian rodent thought to have died out more than 150 years ago.
However, according to research published this month in PNAS, the mouse has been residing on numerous islands in Western Australia the entire time. Researchers from the Australian National University sequenced the genomes of eight extinct Australian rat species using 184-year-old museum specimens and then compared them to 42 surviving cousins.
“We compared the DNA of Gould’s mouse, which was considered to be extinct, to the DNA of all extant native rodent species. The study’s principal author, Emily Roycroft, a postdoctoral fellow at the Australian National University, said, “What we found was that it was genetically indistinguishable from another extant species, the Shark Bay mouse.”
“At first, we assumed the Gould’s mouse only resided in New South Wales and Victoria, but the findings of our research show that it formerly spanned the whole Australian mainland.”
Mapping the genomes of mice Australia has the world’s greatest documented rate of animal extinction.
34 land-roving mammal species have vanished from the landscape since European colonization started in 1788. Rodents have been disproportionately affected, accounting for 41% of animal extinctions since the arrival of humans.
“When we first started the research, our goal was to look at the links between ancient Australian rodents and current species to see how much genetic diversity they had before they went extinct,” Roycroft explained.
The evolutionary researchers did this by extracting DNA from 87 museum specimens and mapping out the genomes of the chewing mammalian species. According to Roycroft, knowing a population’s genetic diversity can assist ecologists to figure out how much the advent of Europeans contributed to their demise.
One theory for the catastrophic extinction of Australian rodents is that they were already in decline owing to genetic variety loss. When ecologists sequenced the genomes of two additional Australian species, the endangered Tasmanian devil, which is now extinct on mainland Australia, and the extinct Thylacine, a bigger carnivorous marsupial commonly known as the Tasmanian wolf or Tasmanian tiger, they discovered something similar.
Before colonization, these two species’ genetic diversity was rapidly dwindling, indicating that their numbers were already dwindling, making them more vulnerable to intruders. To put it another way, Europeans did not cause their extinction; rather, they hastened it.
However, the study discovered that this was not the case when it came to rodent extinction. In fact, before the late 18th century, there was no indication of diminished genetic variety in extinct species, indicating that their populations were vast and robust. Their fast demise after the advent of Europeans indicates that genetic diversity does not always safeguard species from extinction.
“This demonstrates how severe the effects of European colonization, such as imported predators and land clearance, have been, with species that were formerly common becoming extinct in less than 200 years,” Roycroft added.
The importance of rodents in the Australian ecology
The fast extinction of Australia’s furry animals may have a disastrous influence on nearly all of the country’s ecosystems, not just on scampers and squeaks. They may be found in a variety of ecological niches, from deserts to the wet reaches of the coast.
Local rodents are essential ecosystem engineers and play a vital role in Australian ecosystems as consumers of plants, fungi, and invertebrates, as well as a prey supply for other native species, according to Roycroft. “The continuing extinction of native rodents in Australia has the potential to result in ecological collapse.”
Understanding the genomes of extinct species, according to Roycroft, can aid conservation efforts for living species.
“Our research demonstrates how much information we can glean from museum specimens on species that might otherwise be lost to extinction,” she added. “We can learn more about the wider pattern and speed of extinctions if we can generate this sort of data across all of Australia’s native species, not just rodents.”
Future genome sequencing efforts may reveal more surviving species formerly assumed to have gone off the face of the earth, however, this seems improbable. But, for the time being, we know the Gould’s mouse is still scuttling in Shark Bay, which is already well-protected.