Koalas from a population north of the Brisbane River appear to have evolved a unique genomic immunity to the killer retrovirus threatening their species, as discovered by researchers from The University of Queensland (UQ) and the University of Massachusetts — and it could assist with efforts to save the beloved but endangered marsupial.
Koala retrovirus suppresses the koala’s immune system and makes them more vulnerable to other infections like chlamydia which has ravaged populations in Queensland and NSW. It has also been linked to lymphomas that have claimed the lives of many captive koalas.
The new discovery, led by UQ Research Fellow Dr Michaela Blyton and published in the journal [_Cell_](https://www.sciencedirect.com/science/article/abs/pii/S0092867425001916?via%3Dihub), shows that Sunshine Coast hinterland koalas have developed ‘adaptive genomic immunity’ to the retrovirus in their DNA, similar to how an immune system can adapt after exposure to pathogens.
“What we found is that there is a single genetic switch that has been activated in about 30% of the koala population in the Sunshine Coast hinterland, suppressing the retrovirus,” said Professor Keith Chappell, a virologist with UQ’s Australian Institute of Bioengineering and Nanotechnology.
“This is in contrast to what we found in the population on the Gold Coast, where this adaptation is almost completely absent.”
The researchers were also thrilled to discover the adaptation is apparently spreading through the northern koala population. While evolutionary timescales mean it will take many generations to spread across the entire subpopulation on its own, targeted breeding programs could help to speed the process up.
“Because this ‘genomic immunity’ can be inherited, the discovery suggests koalas with the trait could be used in breeding programs to reduce the susceptibility of other populations to the retrovirus, like on the Gold Coast,” Blyton said.
Chappell said retroviruses can alter the genetic code of a host species, and about 8% of human DNA is from infections over hundreds of millions of years.
“In contrast, the koala retrovirus only entered the marsupial’s genome in the past few thousand years, which is really recent in evolutionary terms,” he said.
“Out of all the species on the planet, this is the only one where we can see a genetic response to a retrovirus in real time, rather than looking at responses to things that got into the genome millions of years ago.
“This allows the researchers to study exactly how these iconic critters are responding — it’s actually a pretty amazing situation.”
While there are many other more acute threats to koalas than the retrovirus, the researchers believe that koalas with this adaptive immunity could provide more resilient animals to repopulate areas where koala numbers have been decimated by disease. They added that the breakthrough has opened the door to more research looking at other positive adaptations in koalas across Australia, contingent on future funding.
Image caption: A South East Queensland koala, part of a population that has developed the unique genomic immunity.