A new DNA-based approach to studying invasive mammalian predators

A project undertaken at the Institute for Applied Ecology, University of Canberra and supervised by Oliver Berry and Stephen Sarre

The Red Fox (Vulpes vulpes) has wreaked havoc on mainland Australia’s environment and agricultural production since its introduction in the 1870s. Over the same period Tasmania has remained virtually fox-free, allowing its unique biodiversity to remain relatively pristine. In September 2001, a fox was shot in northern Tasmania and since then, several others have been discovered. These foxes are believed to have been part of a deliberate, illegal introduction of several individuals to the island since 1998.

The fox incursion into Tasmania is potentially a disaster of immense biological and economic significance. If the fox becomes established, 78 native vertebrate species would be at risk. The establishment of foxes would also pose a significant threat to the Tasmanian pastoral industry with conservative estimates of the potential cost of fox establishment in Tasmania in the order of $20 million/year.

In order to better target control, we developed a DNA detection approach aimed at identifying fox traces particularly scats (faeces). We developed a robust PCR test for foxes that amplifies many times fox DNA present in a scat. Through extensive field trials, we demonstrated that we can successfully identify 100% of fox scats even when the scats have been in the field for 3 months. We have since developed this approach to include other large carnivores present in Tasmania.

Using our PCR approach, we have successfully identified as fox, a scat collected near Conara, a blood sample collected from a chicken coop in Hobart, and the remains of an 8-week-old road-kill from near Devonport. Our approach has now been adopted as the method of choice for identifying fox traces in Tasmania and acts as a trigger for control action in that state.

The longer fox populations remain in Tasmania, the less likely it is that foxes will have a small and localized distribution. As a result of this work funded by the Hermon Slade Foundation, we are embarking on a large-scale and intensive survey of Tasmania involving the Invasive Animals CRC, the Fox Free Tasmania Taskforce, interested local communities and the relatively simple process of scat collection. These collections would appear to represent the best opportunity for locating and determining the extent of fox populations and thereby providing the opportunity for targeted fox eradication.

Captions to Figures

Figure 1. Fox (Vulpes vulpes). [Photo by Steve Lapidge].

Figure 2. Potential fox scats are washed in a buffer to extract the cells from the outside of the scat. DNA is subsequently extracted from those cells. [Photo by Nicki Mitchell].

Figure 3. Typical output from the PCR analysis of trace fox samples. Samples 1 and 2 were taken from different tissues obtained from the remains of a roadkill fox dead for 8 weeks before being found. The PCR DNA products are run through a gel of agarose and separated on the basis of size. PCR product is not evident in Sample 1 but clearly present in Sample 2. The letters A,B,C refer to different dilutions of the extracted DNA. Controls are included with the analysis to detect PCR failure or contamination: + = positive control (known fox DNA); - = negative control (no DNA). The universal band is a fragment that should be amplified in the presence of any mammalian DNA, not just fox. [Photo by Niccy Aitken]

 
Figure 1. (Click on image to enlarge)

Figure 2. (Click on image to enlarge)

Figure 3. (Click on image to enlarge)