The most comprehensive genetic assessment of koala populations to date has provided fascinating insights into how the species responded to past climate change, and highlights the critical role of museums in supporting ongoing conservation efforts.
The koala (Phascolarctos cinereus) is one of Australia’s most iconic native species. A unique marsupial that lives in the forests and woodlands of eastern Australia, koalas are best known for their sleepy lifestyle and highly restricted diet of Eucalyptus leaves. While few other marsupials have enjoyed the same level of publicity as the koala, unfortunately this attention has not translated into effective species management.
Koala populations in Queensland and New South Wales – which are now listed as endangered – have experienced rapid and widespread declines due to disease, dog attacks and habitat loss caused by land clearing, urbanisation and climate change. The catastrophic ‘megafires’ of 2019-2020, which burnt over 10 million hectares and resulted in the deaths of up to 8,000 koalas, represent a particularly stark example of the extreme environmental disturbances expected to increase due to climate change. However, another less obvious threat to the continued survival of the koala is the loss of genetic diversity. The loss of genetic diversity from small, fragmented populations has been shown to increase their risk of extinction due to both inbreeding (i.e. mating between close relatives), and a reduced ability to adapt to rapid environmental change. Therefore, the maintenance of genetic diversity by maintaining large, interconnected natural populations, or its augmentation through artificially assisted gene flow (i.e. wildlife translocations), is critical for conserving threatened koala populations in the face of existing and emerging threats.
Currently, relatively little is known about how genetic diversity is distributed amongst koala populations across Australia, and even less is understood about the climatic and evolutionary processes that have created these differences. To answer these questions, a group of scientists, led by researchers at the Australian Museum, have sequenced the protein coding gene regions, or “exons”, of 259 koalas from 92 locations across the species’ geographic range. This represents the most comprehensive investigation of koala genetics to date. Furthermore, by exploiting recent advances in the fields of genomics and bioinformatics, we were also able to collect genetic information from historical Museum specimens, many of which are from areas where koala populations no longer exist (e.g. metropolitan Sydney). Our results indicate that, while all koalas belong to a single species, five distinct groups or population clusters currently exist across Australia. It is estimated that these population clusters first diverged approximately 430,000–300,000 years ago, during a major climatic shift in the middle-late Pleistocene and have since experienced alternating periods of connectivity and isolation as the Australian environment has continued to change over time.
Additionally, our exon dataset allowed us to delve into the complex relationship that exists between climate and genetic diversity in koalas. While some populations do appear to have adapted genetically to local climatic conditions, we also found evidence for repeated, climate-associated range contractions in koalas across eastern Australia. This suggests that geographically isolated refugia (areas where animals can survive during periods of unfavourable environmental conditions), may have played a more important role in the survival of the koala through the cool-dry Pleistocene glacial cycles than genetic adaptation alone. This highlights the importance of aligning the conservation of genetic diversity with the protection of core koala habitat to increase the resilience of threatened populations.
Our findings also have a number of other important implications for koala conservation. We have demonstrated that the current management divisions used by state governments do not accurately reflect the distribution of genetic diversity among existing koala populations, indicating that care must be taken to ensure that established conservation frameworks do not artificially restrict the movement of individuals (and the potentially critical genetic diversity that they represent) between previously interconnected regions.
Finally, we recommend that koala populations should be prioritised for conservation action based on the scale and severity of the threatening processes that they face, rather than placing too much emphasis on their perceived value (e.g. as reservoirs of potentially adaptive genetic variation), as our data indicate that the majority of existing genetic variation in koalas is found amongst individual animals. As such, the loss of koalas from any part of Queensland or New South Wales represents a potentially critical reduction of genetic diversity for the species. Put simply, there is no such thing as a low priority koala!
Dr Matthew Lott, Research Assistant, Australian Centre for Wildlife Genomics, Australian Museum Research Institute.
Dr Greta Frankham, Research Assistant, Australian Centre for Wildlife Genomics, Australian Museum Research Institute.
Dr Mark Eldridge, Principal Research Scientist, Terrestrial Vertebrates, Australian Museum Research Institute.
Lott, M. J., Wright, B. R., Neaves, L. E., Frankham, G. J., Dennison, S., Eldridge, M. D. B., Potter, S., Alquezar-Planas, D. E., Hogg, C. J., Belov, K., & Johnson, R. N. (2022). Future-proofing the koala: Synergising genomic and environmental data for effective species management. Molecular Ecology, 00, 1– 21. https://doi.org/10.1111/mec.16446