Smells like home: Assessing the differences in odour profiles of Shingleback lizards

As part of her PhD research, Dr Amber Brown, with supervisors Dr Greta Frankham, Dr Maiken Ueland and Dr Barbara Stuart, assessed Shingleback lizard odour profiles across the species distribution. This resulted in a new method of detecting and identifying this highly trafficked and smuggled species.

Odour is commonly used in the detection of illegally smuggled objects. It may or may not come as a surprise that the odour of living organisms is influenced by many factors, including habitat, diet and genetics. In our new study, the odour profiles of Shingleback lizards (Tiliqua rugosa) were assessed across their species distribution to form the basis of a new method of detecting and identifying this highly trafficked and smuggled species.

The analysis of biogenic volatile organic compounds (BVOCs), or the chemical compounds responsible for odour, has been utilized in many fields of forensic investigation. Specifically, BVOCs have been targeted for detection (e.g., ignitable liquid residues, human remains) or identification (e.g., drugs) purposes. To complete this analysis, the entire range of BVOCs emitted by a target (known as a volatilome) are analysed using sensitive analytical instrumentation.

BVOCs are also emitted by living organisms, although studies of living organism volatilomes have been limited. We were interested in investigating volatilomes as a future method for detecting illegally traded live wildlife contraband. To do this, we would first need to know how volatilomes differed across a species distribution as it has been previously shown that volatilomes are influenced by dietary, genetic and environmental factors. However, it was unclear how much variability is attributed to habitat.

We had previously published a sampling method for Shingleback lizards, as they are one of the species most highly trafficked out of Australia. The Shingleback distribution extends over one million square kilometres, ranging from the Australian east coast through South Australia, to the islands off the coast of Western Australia. Shinglebacks inhabit many Australian environments, including deserts, saltbush, grasslands, mallee, shrublands, coastal dunes and woodlands. Depending on the environment and season, Shingleback diets change with access to different food items.

To determine whether or not targeting BVOCs for the detection of Shinglebacks being illegally trafficked in transit was a viable forensic option, Shinglebacks were sampled across their range to find BVOCs that were shared across all habitat types. We also aimed to determine whether volatilome assessments could help determine geographic origin(s) of trafficked Shinglebacks post confiscation and how volatilomes differed from their captive counterparts.

Eleven habitat types were sampled across the Shinglebacks range; 44 compounds were found to be shared across all habitat types and were identified as potential detection targets. It was determined that volatilome profiles differed across all habitat types, likely associated with dietary preferences or metabolic states. This work also determined that captive Shinglebacks' volatilomes differed from their wild counterparts. The volatilome of one confiscated Shingleback, whose geographic origin was known, but which had been in captivity for over a year, was compared to a volatilome from the wild. This Shingleback's profile was found to more closely resemble the average captive profile compared to the average habitat profile from which it originated.

This work has set the foundation for future live animal volatilome analysis and its application in wildlife forensic science. With the application of this new technique, we can more accurately detect trafficked animals and inform our current conservation and biosecurity policies.