A MULTINATIONAL research project is figuring out why some koalas are more susceptible to diseases like cancer and chlamydia and is helping us to understand evolution at the same time.
It has seen scientists find a type of immunity that protects koala DNA from viruses.
A team of scientists from The University of Queensland and University of Massachusetts Medical School is studying tissue samples from koalas to understand how a unique type of cell responds to retrovirus infections, which cause diseases like chlamydia and cancer.
Keith Chappell, from UQ's School of Chemistry and Molecular Biosciences, said the discovery of this immune system response could open an entirely new research field.
"The genomes of all animals, including humans, contain a large amount of viral sequences that are the result of infections that occurred millions of years ago," Dr Chappell said.
"The koala is the only species in which a retrovirus is known to have recently infected the germline cells - the ones that make sperm and eggs.
"This means that some koalas are born with koala retrovirus A - known as KoRV-A - in their genome, making them more susceptible to diseases such as chlamydia and cancer.
"It is well known that viruses have driven the evolution of humans and animals over thousands of years, yet understanding how germline cells respond to infection has been a mystery for scientists.
"It was previously thought that the process of natural selection kept levels of viral elements in check within the genome, meaning that it would be survival of the fittest for the koala.
"However, our findings show that there are immune response like pathways within a koala's germline cells that can actively fight back against the invading virus."
Professor William Theurkauf from Massachusetts said the germline cells could recognise the sequence of KoRV-A as an invading virus and not a gene, and would mount an initial defence.
"Just like the human body launches an immune response to invading viral and bacterial infections, our findings suggest that germline cells mount an attack to chop up the viral sequences," Professor Theurkauf said.
"This prevents the retrovirus from inserting more and more copies into the genome of the offspring and thereby protects the next generation against what would be compounded effects of disease."
The study was funded from the US National Institute of Health, the Australian Research Council and the Chinese National Natural Science Foundation.
