Kangaroo Island Koalas face hidden genetic threats despite abundance

Kangaroo Island koalas show longer and more frequent stretches of identical DNA inherited from both parents. Scientists call these runs of homozygosity, a clear marker of inbreeding. (Image: Flinders University)

At first glance, Kangaroo Island in South Australia looks like a koala sanctuary. The island holds a large, disease-free population, often seen as a conservation success story. But is this picture really so simple?

Why Are Scientists Concerned About Koalas Here?
New research from Flinders University has revealed a worrying legacy. Although the population is abundant, its genetic diversity is far lower than mainland groups. Researchers compared Kangaroo Island koalas with those in Victoria and Queensland using whole-genome sequencing. They found much more inbreeding, which could make these animals less able to cope with future threats.

How Did This Problem Begin?
The history goes back to the 1920s. Fewer than two dozen koalas were moved from Victoria to Kangaroo Island to save them from hunting and habitat destruction. But those animals already came from a small and genetically limited group. Today, east coast koalas are endangered, struggling with habitat loss, bushfires, road expansion and disease. In contrast, Kangaroo Island koalas grew in number, even after bushfires destroyed more than half of the island in 2019–20.

(Image: Flinders University)

What Have Scientists Discovered About Their Genes?
Lead author Dr Katie Gates explained that while numbers are high, genetic health is poor. The team found long stretches of identical DNA inherited from both parents, a clear sign of inbreeding. Harmful genetic variants were also more common, raising the risk of fertility issues and developmental abnormalities. Some problems have already been seen in captured animals. Although the island population has so far resisted chlamydia and koala retrovirus, scientists warn that its limited genetic toolkit may leave it open to future outbreaks.

What Can Be Done to Protect Them?
The researchers suggest ‘genetic rescue’, introducing carefully selected koalas from more diverse mainland groups. Senior author Professor Luciano Beheregaray said Kangaroo Island could remain an important refuge, but without action this ark could become a trap. The study stresses the need for regular genetic monitoring and stronger strategies to boost diversity.

The findings highlight a bigger message for wildlife protection. While islands and fenced reserves offer safe havens, they cannot stand alone. To secure the future of threatened species, conservation must pair physical protection with genetic management.