A classification conundrum or a new subspecies in the making? Perhaps, it’s both.

AMRI scientists have found an unusual population of black-footed rock-wallabies from the central deserts of Western Australia – and surprisingly, the population didn’t seem to belong to any known subspecies…

Museum scientists are often taxonomists – that is we study, classify and describe biodiversity. But sometimes, we encounter unusual individuals or populations that defy our conventional classification schemes. While at first puzzling, these anomalous situations can help us shed light on the evolutionary processes that generate biodiversity.

The black-footed rock-wallaby, Petrogale lateralis, is patchily distributed across much of central and Western Australia. Within this widespread species, five distinct subspecies are recognised. Each are identified by the unique number and/or shape of their chromosomes, as well as their fur colour and body measurements.

In the 1990s, a small and anomalous population of black-footed rock-wallabies was identified at the Townsend Ridges near Warburton in central eastern Western Australia. These rock-wallabies had a mix of chromosomes from two different black-footed rock-wallaby subspecies. Some chromosomes were characteristic of the nearby warru, P. l. centralis found in central Australia and other chromosomes were typical of the wiliji, P. l. kimberleyensis which occurs on the southwest edge of the Kimberley, 1000 km away. Could these Townsend Ridges wallabies represent a novel hybrid zone between these two subspecies?

To test for this, AMRI scientists recently conducted genetic research where we generated DNA sequence data from a mitochondrial DNA gene, which resulted in further complexity. While one Townsend Ridges individual had DNA typical of P. l. centralis (as expected), the remaining individuals had DNA most closely related to other black-footed subspecies and not to P. l. kimberleyensis. Not at all what we predicted!

Although the Townsend Ridges rock-wallabies do appear to represent a hybrid zone, the number and identity of the black-footed rock-wallaby subspecies involved remains uncertain. However, what is clear is that by combining genetic material from different subspecies (through hybridisation) the Townsend Ridges rock-wallabies could be on the way to forming their own new subspecies. So, while we might not be able to taxonomically classify the Townsend Ridges rock-wallabies, they have given us something more valuable; insight into the sometimes messy and complex processes by which new biodiversity can be generated.

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

Dr Sally Potter, Research Associate, Australian Museum Research Institute; and Australian National University.