A new DNA study suggests there is limited gene flow between koalas in Port Stephens because they are trapped in isolated patches of habitat, separated from other koalas by roads, houses, buildings and farmland.
The World Wide Fund for Nature-Australia commissioned the report as part of its Koalas Forever plan to double koala numbers in eastern Australia by 2050.
“WWF is concerned about any koala populations where gene flow may be limited. They can lose genetic diversity and become less able to adapt to climate change or fight off new diseases,” said Darren Grover, WWF-Australia’s Head of Healthy Land and Seascapes.
“Habitat fragmentation, which impedes gene flow, is a major problem for koalas and other species. That’s why a major focus of Koalas Forever is to protect existing habitat, regenerate cleared forests, and to plant tree corridors to reconnect isolated populations,” he said.
The study analysed DNA obtained from koala droppings. Independent researchers OWAD Environment used their specially bred and expertly trained detection dogs Taz and Missy to collect koala scats in November 2018, July 2019 and May 2020.
The scats were then analysed by WildDNA, an expert laboratory at Federation University Australia.
DNA from 39 unique individuals was sampled – 19 females and 20 males.
Analysis revealed there are two main koala populations or ‘genetic clusters’ in Port Stephens: koalas in the Tilligerry and Tomaree Peninsulas, referred to as ‘peninsula’ koalas, and those further west in Karuah, Ferodale and Balickera, referred to as ‘inland’ koalas.
Genetic data showed these two clusters were once connected. However, the report says peninsula koalas “are now significantly different from those sampled further inland suggesting that gene flow between peninsula and inland koalas has been restricted over recent generations”.
“Peninsula koalas were also found to be less genetically diverse than inland koalas, suggesting that peninsula koalas may be losing genetic diversity due to a lack of successful migration from outside the peninsula”.
Among inland koalas, despite minimal distances separating them, fine-scale analysis suggests gene flow is limited. Koalas sampled in Balickera and Ferodale are separated by the Pacific Highway.
The report cautions that “sample sizes … are small and further sampling would be required to gain a greater insight into the genetic diversity of koalas across the region”.
OWAD’s Olivia Woosnam, a koala conservation ecologist, said koala habitat remained largely connected in Port Stephens until the 1940s when tree clearing ramped up due to urbanisation and infrastructure development.
“Now koalas are confined to smaller patches of forest surrounded by inhospitable habitat such as houses, buildings, roads and farmland. It’s difficult for koalas to disperse and migrate, as they are programmed to do, and often proves fatal,” Ms Woosnam said.
“Previous research shows that isolated populations rapidly become genetically differentiated, and lose genetic diversity due to loss of gene flow. This is likely what has happened on the peninsula, and appears to be starting to happen inland too.
“To improve gene flow in Port Stephens, existing forest must be conserved and groups of koalas reconnected by reinstating safe corridors.
“Functional koalas crossings are also needed to enable koalas to safely traverse roads and highways.
“For example, a well-designed crossing structure over the Pacific Highway could help facilitate gene flow between Balickera and Ferodale, which would benefit koalas on both sides of the highway.
“Dead Koalas are regularly reported on the highway. We know they want to cross but there is no safe way. Genetic analysis results suggest that few seem to make it across successfully,” she said.
Darren Grover said more research is needed into koala genetics, using a range of techniques, to compare different populations.
“WWF welcomes the recently announced $1 million investment by the NSW and Federal governments to map the genes in 400 koalas.
“Understanding koala population structure is essential to effectively protect the species. Ultimately the most important action needed is to safeguard existing habitat, regenerate cleared forests, and plant corridors to reconnect isolated groups,” he said.
Koalas Forever is a key project in WWF’s Regenerate Australia plan – the largest and most innovative wildlife and landscape regeneration program in Australia’s history.
Under Regenerate Australia, WWF is seeking to raise $300 million program, over 5 years, to help restore wildlife and habitats, rejuvenate communities impacted by the bushfires, boost sustainable agriculture and future-proof our country.
To help go to wwf.org.au/savekoalas
OWAD’s detection dogs Taz (left) and Missy (right) travelled 137km searching for evidence of koalas in Port Stephens