Our recent study of genetic diversity within brush-tailed rock-wallabies (Petrogale penicillata) in south-eastern Australia have revealed some surprises. Not only have we determined the most appropriate management strategy for this endangered species, but we have also discovered the genetic footprint of ancient and dramatic environmental change.

At the time of European settlement, brush-tailed rock-wallabies were found from western Victoria to south-east Queensland. However, our genetic analysis has revealed three highly divergent lineages within the species, each restricted to a discreet geographic area.

Male brush-tailed rock-wallaby <i>Petrogale penicillata</i>
Male brush-tailed rock-wallaby (Petrogale penicillata) at rest Image: Katherine Tuft
© Katherine Tuft

This suggests that hundreds of thousands of years ago, during the Pleistocene ice-ages when the climate was cooler and drier, brush-tailed rock-wallaby populations contracted to only three small areas (refugia). Subsequently, when the climate again became wetter and warmer, these remnant populations expanded leaving no sign of these dramatic events except for a clear ‘footprint’ in their DNA.

The decline of the brush-tailed rock-wallaby in the last 200 years has impacted each genetic lineage differently. The situation for the southern-most lineage is particularly serious with less than 20 individuals surviving along the Snowy River in Victoria.

Although brush-tailed rock-wallabies from the central lineage remain relatively widespread in New South Wales, from the southern Hunter Valley to Kangaroo Valley, they too are endangered since only small scattered populations remain, and a few more go extinct every year. The northern lineage is currently the most secure, inhabiting the gorges of north-east New South Wales and south-east Queensland, but the ongoing decline of brush-tails leaves little room for complacency.

Black-flanked rock wallabies (Petrogale lateralis lateralis)
A pair of black-flanked rock-wallabies (Petrogale lateralis lateralis) located in Kalbarri National Park in August 2015. Image: Remy Vignals
© Remy Vignals

We also examined levels of genetic diversity within brush-tail populations. Most northern populations were highly variable, but within the remnant southern colonies, levels of diversity were low and most surviving individuals appeared closely related.

This suggests there is now no gene flow amongst these colonies, and they continue to lose diversity and become inbred, increasing their likelihood of extinction. This raises the dilemma of how to conserve these genetically unique local populations.

A solution is to collectively manage populations within each lineage as identified by our analysis, rather than focus on individual local populations. This strategy has been adopted for the central and southern lineages, with individuals being transferred between wild populations within each lineage to recreate natural gene flow, bolster genetic diversity and counteract inbreeding. It is hoped that this strategy will ensure that the hills remain alive with rock-wallabies.

Dr Mark Eldridge
Senior Research Scientist

More information:
Hazlitt, S.L., Goldizen, A.W., Nicholls, J.A. and Eldridge M.D.B. 2014. Three divergent lineages within an Australian marsupial (Petrogale penicillata) suggest multiple major refugia for mesic taxa in southeast Australia. Ecology and Evolution.