Researchers from the Australian National University have discovered that the delicate mouse, a native mammal, is not a single species, but three distinct ones.

The delicate mouse (Pseudomys delicatulus), also known as the little native mouse, is the smallest of all Australian native mice, 55 to 75 mm long and weighing 6 to 15 grams. Discovered in 1842, it was thought to be one species spanning a large stretch of the country from the Pilbara in Western Australia, across parts of the Northern Territory and through Queensland down to the New South Wales border.

Using genetic technology, however, scientists at ANU and CSIRO realised the mouse was three species: the western delicate mouse or Pilbara delicate mouse, eastern delicate mouse, and northern delicate mouse. (The untrained eye might struggle to tell the species apart, however.)

“Identifying undescribed species and giving them official names goes a long way to making sure they’re properly looked after,” the lead author, Dr Emily Roycroft, an evolutionary biologist from ANU, said.

The discovery is crucial for the future of the tiny mouse, Dr Roycroft argues. 

“The two new species haven’t had any conservation or research attention, because we didn’t know they were there,” Dr Roycroft said. 

“We don’t know, for example, if population declines have gone undetected as a result of all three species being assessed as a single unit. 

“The delicate mouse has not been a conservation priority – but that’s because it was thought to have a distribution three times larger than it actually does. This will allow us to reassess.” 

Dr Roycroft said the delicate mouse differs from the mice you might come across in your home or backyard in a few important ways. 

“House mice, black rats and brown rats are invasive species brought to Australia since European colonisation. They’re very different to native rodents, both evolutionary and ecologically. They compete with our native species for resources. 

“Delicate mice are part of a group of native rodents that have been evolving in Australia for the last five million years. They’re a crucial part of Australia’s natural environment and ecosystems. 

“Delicate mice are our smallest Australian rodent. They can weigh as little as six grams, so they’re really tiny.” 

The study also found delicate mice are excellent adaptors to their environment, whether that be arid desert or forest.

The study has been published in Molecular Ecology. 

Three years ago, Dr Roycroft’s team discovered that Gould’s mouse, considered extinct, was the same as a living species.