Here’s the lowdown from AusBiz
Kangaroo Island in South Australia has long been hailed as a conservation success story. With a large, disease-free population, the island’s koalas have become a symbol of resilience, even after the devastating 2019–20 bushfires that burned more than half the island.
However new research from Flinders University suggests there’s a less visible threat: low genetic diversity and high levels of inbreeding that could compromise the population’s long-term survival.
Getting to the crux of the koala concern
Using whole-genome sequencing, researchers compared Kangaroo Island koalas with their mainland counterparts in Victoria and Queensland. The findings were striking. Despite healthy population numbers, the island koalas showed significantly less genetic diversity and more signs of inbreeding. This stems from their history: fewer than 20 koalas were introduced to Kangaroo Island in the 1920s, all from an already small and genetically limited Victorian population.
Meanwhile, koalas along the east coast are listed as endangered under the Environmental Protection and Biodiversity Conservation Act (since February 2022), their populations hammered by habitat loss, disease and climate impacts. The Kangaroo Island population, while relatively stable, may not be as secure as it seems.
Meet a pro who can shed more light
Lead author Dr Katie Gates explains: “Kangaroo Island koalas are a successful conservation story in terms of population size. But their genetic health tells a different story. Their limited diversity and high inbreeding means they might struggle to adapt to future threats like disease or climate change.”
The Flinders University team found extensive runs of homozygosity — long stretches of identical DNA inherited from both parents — a hallmark of inbreeding. Harmful genetic variants were also more likely to be present in double doses, increasing the risk of fertility issues and developmental abnormalities. Indeed, some of these abnormalities have already been observed in captured koalas.
So far, the population has resisted infectious diseases like chlamydia and koala retrovirus, but researchers warn their reduced genetic toolkit leaves them more vulnerable to outbreaks in the future.
To protect against this risk, the team recommends “genetic rescue” — carefully introducing koalas from more diverse populations to strengthen the gene pool.
Senior author Professor Luciano Beheregaray says this kind of intervention is vital:
“Kangaroo Island has the potential to remain an important conservation refuge for koalas. But without genetic management, this ‘ark’ could become a trap. Our work highlights the importance of ongoing genomic monitoring for species managed in isolation.”
The study also serves as a broader reminder for wildlife conservation. Islands and fenced reserves may offer immediate protection, but without strategies to bolster genetic diversity, they risk creating fragile populations ill-equipped to face long-term challenges.
Some lesser known facts about koalas
Meet Australia’s pouch bear
The koala’s scientific name, Phascolarctos cinereus, reveals a lot about it. Phascolarctos means “pouch bear” in Greek, while cinereus means “ash-coloured” in Latin, describing the animal’s grey fur. The name was first recorded by British zoologist George Perry in 1810.
Are koalas actually bears?
Despite their teddy-bear appearance, koalas aren’t bears at all. They’re marsupials, making them more closely related to kangaroos and wombats.
Koalas are picky eaters — and often sleepy
A koala’s diet revolves almost entirely around eucalyptus leaves, including flowers, buds, stems and bark. Eucalyptus also acts as a sedative, which explains why koalas spend so much of their time asleep. Research shows compounds in the leaves influence neurotransmitters in the brain, creating a hypnotic, drowsy effect.
But koalas aren’t indiscriminate leaf-eaters. Out of Australia’s 700-plus species of eucalypt, they rely on just a handful. For instance, in northern New South Wales they prefer Forest Red Gum, Tallowwood and Swamp Mahogany. This pickiness explains their limited distribution and why habitat loss has hit them so hard.
The meaning behind “koala”
Koalas obtain most of their hydration from eucalyptus leaves. Their name comes from the Dharug language of the Greater Sydney region, where gula or gulamany means “no drink.” They only seek out water during extreme heat or drought.
The chlamydia challenge
One of the most pressing health issues facing koalas is chlamydia, caused by the bacteria Chlamydia pecorum. It can lead to blindness, pneumonia, infertility and death. Fortunately, recent research has produced a vaccine that boosts koalas’ immune response. Thanks to the Friends of the Koala Hospital and the University of the Sunshine Coast, vaccinated koalas now have a fighting chance against the disease.
How long do koalas live?
In the wild, koalas generally live 10–15 years, though females often outlive males. In captivity, they can live longer. The oldest wild koala cared for at Friends of the Koala was a 19-year-old female.
Kangaroo Island’s koalas remain a conservation beacon, but this new research reveals that numbers alone don’t guarantee security. Genetic health matters just as much as population size. With careful management, including the possibility of genetic rescue, Kangaroo Island could continue to serve as a refuge for this much-loved species — but without it, the future may be more fragile than it seems.
A version of this article first appeared in Molecular Ecology.
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