Image for Tasmanian DNA fox-positive scats

In late 2010 the out-going manager of the Fox Eradication Program told Tasmanians that the strongest evidence they had of foxes existing in Tasmania was the 50-plus scats confirmed by molecular technology to contain fox-DNA.

A genetic technology allowed a testing laboratory in Canberra to detect marker genes specific for red fox, Vulpes vulpes.

Since 2005 this DNA-testing capability has been used to support the Tasmanian fox program.

The first confirmed DNA-fox positive was recovered in February 2005 at Conara in the central Midlands; however, it was only confirmed as ‘positive’ seven months later (September 2005). DNA-contamination in the testing laboratory had caused the facility to be closed for ‘de-contamination’. Records indicate that DNA-contamination had halted scat testing in that laboratory on at least three occasions.

At the time this scat was publicly reported the new technology was heralded by the fox program management (and by the Minister responsible for the program) to be ‘the most compelling evidence of foxes found so far’.

It was one of 180 carnivore faeces collected from areas that the program regarded as fox ‘hot-spots’.

A spokesperson for the Canberra testing laboratory, Dr Tony Peacock said, “one sample came back with a DNA sequence that matched the fox. This result confirms that the scat was definitely from a fox”. 

A spokesperson for the Tasmanian Government program, John Whittington said, “What it shows, without any doubt, is that there was a fox near Conara in February [2005]”.

This public announcement of a DNA-fox positive scat came within days of the announced Invasive Animal CRC review of the fox program. The Review recommended the Government-funded program shift its emphasis to recovering evidence such as scats in Tasmania and submitting them for DNA testing.

The scats recovered for each calendar year is presented in Table 1.

Contrary to Mr Whittington’s definitive conclusion that the first DNA-fox positive scat proved “there was a fox near Conara in February”; the gene test only proved that a scat recovered in Tasmania contained fox-specific DNA. The test cannot - of itself - determine whether such a scat is linked to the landscape where it was recovered. Examining such scats for contents that are specific to Tasmania could help to provide that direct link. This would include diagnostic elements such as hair from Tasmanian endemic species such as Tasmanian pademelon (Thylogale billardierii) and Tasmanian bettong (Bettongia gaimardi).

Table 1: Number of scats recovered in Tasmania that confirmed as DNA-fox positive by the University of Canberra’s Invasive Animals CRC molecular testing laboratory in Canberra

Year  No. of scats testing positive
2005  1
2006  5
2007  5
2008  26
2009  17
2010  2
2011        Discontinued

The confirmation of hair from a Tasmanian endemic species in a DNA-fox positive scat would provide a compelling result suggesting the fox that produced that particular scat actually lived in Tasmania.

In addition to detecting DNA-fox positive scats at a given location, the ability to apply molecular techniques to genotype those scats could demonstrate whether any were derived from the same fox (by genotype match). This would offer additional evidence to support the natural likelihood that a fox living in a given area defecated on more than one occasion.

The results of genotyping DNA-fox positive scats to date has not demonstrated that to be the case. Of those scats successfully sequenced for genotype matching, no two scats have identical nucleotide sequences.

It is notable that on several occasions during the scat collecting surveys, using trained scat-detector dogs, more than one DNA-fox positive scat was recovered from the same location on the same day; Table 2 indicates these locations and dates.

Table2: Instances where more than one DNA-fox positive scat was recovered from the same location on the same day. Note: All were confirmed as ‘fox’ by DNA testing, but no genotype results have been presented to date [October 2011].
 
Date  Location  Number of DNA-fox positive scats recovered
10 October 2006  Conara  2 (no genotype result released)
7 May 2008  Spreyton  2 (one scat genotyped & gender id - male)
23 June 2008  Spreyton  2 (one scat genotyped & gender id - female)
16 June 2009  Cygnet  2 (genotyping ‘unsuccessful)

At several Tasmanian sites multiple DNA-fox positive scats have been recovered within days or weeks of each other - Conara (October 2006, three scats); Gladstone (October 2007, two scats); Tunbridge (May 2008, two scats); Longford (June 2008, two scats); Burnie (June-July 2008, two scats and October 2008 two scats). No genotyping results confirm that any of these DNA-fox positive scats are from the same fox.

Faeces have been used forensically and diagnostically as a bio-marker for the presence of a rare species of animal or to identify a specific individual. Visual identification of a scat, as well as smell, and the identification of digested contents can also help in determining the species of origin. In recent decades genetic finger-printing has become widely used to differentiate between similar looking (and smelling) faeces from types of animals with similar diets. Ultimately however, no matter how precise these technologies are, the critical issue is whether the identification of a scat to species links the presence of that species to the landscape that the scat is found in using another form of forensic or diagnostic evidence. Two pieces of objective data from the same location collected over a similar timeframe provides more compelling evidence of the animal’s presence than reliance on the discovery of a scat alone.

Scats are excreta and as such are separate from the animal that produced them. As forensic exhibits, their discovery at a location and with subsequent species-specific DNA testing, one might assume that the scat proves that a particular species of animal is (or was) present at the location where the faeces was collected. It’s a natural assumption to make but, it can only be a qualified assumption. DNA-containing material which is species-specific - like blood, faeces, skin, hair, semen, urine, body tissues cannot - of itself - be conclusive of the presence of the identified species at that scene. Further corroborating (or as the police require - incriminating) material or information would build confidence in an assessment and any conclusion that come from it. 

Fox faeces is excreta from a fox. On its own, no-one can claim that there is (or was) a fox present at the location a scat is found, based solely on that test result. In order to be more convinced about a link between the presence of fox faeces and the presence of a live fox, you need additional results.

Decision-making sufficient to trigger an expensive response must rely on a higher burden of proof - i.e. at least two independent pieces of species-specific information would greatly improve the verification process - e.g. scat and photo; footprint and photo; two or more scats from the same fox.

At the Hotel SoHo on 13 October 2011 the new manger of the FEP Craig Elliott gave a presentation to the Tasmanian Branch of the Australia and New Zealand Forensic Science Society (ANZFSS). He confirmed that none of fox scats found in Tasmania showed a link to the landscape in which they were found. No scats contained unique Tasmanian endemic species and so far there are no two scats genotyped scats identified from the same fox.

Prepared by: David Obendorf
October 2011