Kangaroo Island, in South Australia, is home to a large koala population, largely disease-free, which at first glance seems a conservation success story.
However, a new investigation from Flinders University shows that, because the population began small, it bears a genetic legacy that may make it harder to survive future threats.
Using whole-genome sequencing, the researchers compared Kangaroo Island koalas with populations on the mainland in Victoria and Queensland.
Despite their relatively high abundance on Kangaroo Island, these koalas have far lower genetic diversity and are far more inbred than mainland koalas.
The problem traces back to their history. In the 1920s, fewer than two dozen koalas were moved from Victoria to Kangaroo Island to save the species after hunting and habitat loss had nearly wiped them out. These original koalas came from a population that was already small and genetically limited.
Today, koalas along the east coast of Australia are officially listed as endangered, with ever-smaller and more isolated populations due to deforestation, wildfires, disease, and road development.
On the other hand, the Kangaroo Island koalas have become a symbol of hope for the species, despite the major bushfires that destroyed more than half the island in 2019–20.
Lead author Katie Gates says, “Kangaroo Island koalas are a story of success in terms of population size. But their genetic health tells a different story. Their limited diversity and high rate of inbreeding mean they may struggle to adapt to future threats, such as disease or climate change.”
Flinders University researchers found that Kangaroo Island koalas have much more numerous and longer stretches of identical-by-descent DNA inherited from both parents. Scientists call these stretches homozygosity, and they are a hallmark of inbreeding.
The team also found that potentially harmful genetic variants were more often present in a homozygous state in Kangaroo Island koalas, increasing the likelihood that these variants would manifest in their offspring.
This pattern increases the risk of fertility problems and other developmental issues, consistent with several anomalies found in koalas that were captured.
Although the population has so far resisted infectious diseases such as chlamydia and the koala retrovirus, its reduced genetic toolkit may leave it vulnerable to future outbreaks.
The researchers recommend proactive conservation management, including “genetic rescue”—the careful introduction of new koalas from genetically diverse mainland populations.
Senior author, Professor Luciano Beheregaray, concludes: “Kangaroo Island has the potential to continue to be an important conservation refuge for koalas. But without genetic management, this ‘arc’ could become a trap. Our work underscores the importance of ongoing genomic monitoring for species kept in isolation.”
The findings also carry a broader message for wildlife conservation: although islands and fenced reserves can provide immediate protection, they must be paired with strategies to bolster genetic diversity if they are to continue serving as true refuges for endangered species.
