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Sydney Koalas’ Genetic Diversity Crisis Puts Population at Risk

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March 2, 2025
4 min read

Sydney Koalas’ Genetic Diversity Crisis Puts Population at Risk

Sydney Koalas’ survival is facing a major challenge as new research reveals that while they remain free from chlamydia, their low genetic diversity makes them highly vulnerable to disease outbreaks and environmental threats. Conservationists warn that these koalas, living in south-western Sydney, have limited genetic variation due to inbreeding, which could make them less able to adapt if chlamydia were introduced into the population.

The study examined koalas across key areas, including Liverpool, Campbelltown, Heathcote, Wollondilly, and the Southern Highlands. Findings showed high interrelatedness among the populations, with many koalas having cousin or half-sibling relationships. This limited genetic variation means that if chlamydia were to spread to these koalas, they may not have the necessary resilience to fight off the disease.

One of the biggest challenges is that these koalas live in urbanised areas, restricting their ability to travel and breed with genetically diverse populations further afield. There is some movement between Wollondilly and Campbelltown, but this presents another risk, while genetic mixing could strengthen the population, it could also introduce chlamydia into an environment where koalas lack the genetic defence against it. Conservationists describe this as a classic “Catch-22” situation: increasing genetic diversity may improve survival chances, but it also increases the likelihood of disease transmission.

Beyond disease, Sydney’s koalas are also battling threats from climate change and urbanisation. Habitat loss is a growing concern, as continued development further isolates populations and reduces available food sources. Conservationists stress that protecting and connecting habitats is crucial, but even this must be done carefully to prevent the rapid spread of disease. The challenge is to strike a balance—ensuring koalas have enough space to thrive while minimising the risks associated with increased mobility.

Koalas in Queensland, New South Wales, and the Australian Capital Territory were officially listed as endangered in 2022, with populations declining by nearly a quarter over the past two decades. This highlights a much wider issue facing conservation efforts globally: species with limited genetic diversity are at heightened risk from disease outbreaks and environmental changes, making proactive management essential.

Addressing these concerns requires a multi-pronged approach. Efforts to protect and expand koala habitats must be paired with long-term monitoring of genetic diversity, ensuring that conservation strategies do not inadvertently expose these animals to greater risks. If the right balance can be found, there is hope that Sydney’s koalas can continue to thrive without succumbing to the fate of many populations elsewhere.

A detailed study on their genetic vulnerabilities, conducted by the University of Sydney, highlights the risks they face and can be read in full here.

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