Remnant rock-wallabies: Genetics informs threatened species management

A recently rediscovered rock-wallaby population posed some real dilemmas for management.

The black-flanked rock-wallaby (Petrogale lateralis lateralis) was last seen in Kalbarri National Park, Western Australia (WA), 580 km north of Perth, in 1995 and was thought to be locally extinct. Then in 2015, a pair of rock-wallabies were photographed in the Murchison River gorge, within the Park by a rock-climber. Despite extensive searches along the Gorge no other wallabies were found, suggesting that only this small remnant population had survived, going undetected for decades.

While the rediscovery is good news, the chances of this tiny remnant population surviving long term were slim. Any increase in numbers would be slow, inbreeding and loss of genetic diversity inevitable and the population also faces ongoing threats from introduced predators and competitors, as well as demographic or environmental chance events that could easily result in its extinction.

A solution would be to supplement the remnant Kalbarri population with individuals from other surviving populations, to increase the population size and genetic diversity. But where should these individuals come from? Although formerly widespread across southern and western WA, the black-flanked rock-wallaby has declined throughout most of its distribution and only a handful of populations survive. To help guide management decisions we compared the DNA from the Kalbarri individuals with that from other surviving blank-flanked rock-wallaby populations.

Efforts to trap and directly sample the Kalbarri rock-wallabies were unsuccessful, but some fresh faecal material (scats) was found. Analysis of a section of DNA sequence obtained from each scat showed that the Kalbarri rock-wallabies were genetically distinct from all other sampled black-flanked rock-wallaby populations. They were genetically most similar to rock-wallabies in the Calvert Range, 950 km to the north-east in the Little Sandy Desert which has a very different climate to Kalbarri. Nearer populations at Cape Range (600 km north) and the WA Wheatbelt (500 km south-east) were less closely related but had a more similar climate.

With no obvious source population evident, a variety of factors including, genetics, population size, demography, ecology, environment and logistics, were evaluated resulting in a decision to supplement the Kalbarri National Park population with three females sourced from the WA Wheatbelt. We hope this will secure the survival of the population whilst still preserving any unique Kalbarri genes. Although not without risk, the supplementation was considered less risky than doing nothing which would have most likely resulted in the extinction of the Kalbarri population.

Dr Mark Eldridge, Principal Research Scientist, Terrestrial Vertebrates, Australian Museum Research Institute

Dr Linda Neaves, Post-doctoral Researcher, Australian Centre for Wildlife Genomics, Australian Museum Research Institute and Royal Botanic Garden Edinburgh

More information

• Pearson, D.J., Neaves, L.E., Paxman, M., Desmond, A., Renwick, J., Halley, M., Willers, N. and Eldridge, M.D.B. 2018. Identification of a remnant population of the black-flanked rock-wallaby (Petrogale lateralis lateralis) in Kalbarri National Park, Western Australia and implications for its management. Australian Mammalogy on-line.
• Ralls, K., Ballou, J.D., Dudash, M.R., Eldridge, M.D.B., Fenster, C.B., Lacy, R.C., Sunnucks, P. and Frankham, R. 2018. Call for a paradigm shift in the genetic management of fragmented populations. Conservation Letters 11: e12412