SYDNEY, June 9 (Xinhua) -- A new genomic study has found that koala populations experienced a severe decline around 100,000 years ago, long before humans arrived in Australia, overturning previous assumptions.
The study suggests environmental change, rather than early human activity, was the main driver of the species' population decline, according to a statement of Australia's University of Sydney released Tuesday.
All modern koalas descended from "a single, struggling ancestral population" that survived harsh climate upheavals, such as glacial periods, and fluctuating cold and dry periods as the Australian tectonic plate moved, it said.
As Australia became drier, koala habitats contracted, isolating populations and leading to the extinction of western groups, while a small eastern population "persisted through the harshest glacial conditions," said researchers from the University of Sydney and Texas A&M University in the United States.
"The study rewrites the timeline for the koala's genetic history in Australia," said PhD candidate Toby Kovacs at the University of Sydney.
"By calculating the mutation rate of modern koala populations, we can estimate and build the genetic timeline backwards all the way to 100,000 years ago to get a glimpse of genetic diversity and the sizes of ancient koala populations," said Kovacs, lead author of the study published in Molecular Biology and Evolution.
Using parent-offspring genome sequencing, scientists estimated a koala mutation rate -- about half that of humans -- and applied it to 457 genomes, identifying a sharp bottleneck around 60,000 years ago linked to cold, dry glacial conditions and habitat loss.
Researchers said the findings could aid conservation as modern koalas face threats from hunting, land clearing, bushfires and disease, and have been listed as endangered in parts of eastern Australia since 2022. ■
