Experienced trackers know exactly which species of animals are around from looking at their poo. But to do that, they need to get their hands on a good quality stool. Conditions aren’t always favourable for faecal preservation – rain, insect or other animal activity, health and diet of the animal can all conspire to make traditional identification tricky if not impossible.

The face of a mountain lion. Released by Digital Art here: http://www.flickr.com/photos/digitalart/ under CC-BY licence

The face of a mountain lion. Released by Digital Art here: http://www.flickr.com/photos/digitalart/ under CC-BY licence

This can be a real problem when tracking rare, elusive or endangered species, such as mountain lions. To understand population dynamics and evaluate conservation projects, we need to know how many animals are in which locations. Where the animals are too few and far between to use mark-release-recapture techniques, ecologists are increasingly turning to chemistry for new identification tools.

Genetic analysis seems like the obvious way to go. By analysing DNA found in dung, one can identify not just the species, but the individual animal. This sort of analysis has been demonstrated in a number of species and is now involved several conservation projects. For just £50 +P&P, you can send a sample off to a company in Warwickshire, who can identify most British mammalian species – very useful for determining what species of bat is nesting in your loft, or if you’re not sure whether a fox or a pine marten has been using your privet as a privy.

However, DNA has its problems, especially in degraded samples. With carnivores, predator and prey DNA can become muddled. The DNA itself is also broken down over time, and even simple microsatellite analysis – similar to the DNA profiling methods used by the police –  requires amplification equipment, access to restriction enzymes etc that may be beyond the capabilities of remote field stations. So other biomarkers that can act as a species-specific signature are needed.

Bile acids may be the answer. According to a new paper in Analytical Methods, bile acids are ‘very stable compounds’ that ‘remain chemically unmodified at extreme environmental conditions’ and due to differences in physiology, metabolism and gut bacteria, show marked differences between different species.

The idea of using bile acid composition and concentration as a marker for species is not new. Previous research has identified species from their bile acid profile using thin-layer chromatography, for example. Gas chromatography-mass spectrometry (GC-MS) has been used to identify medically relevant bile salts in human excreta, but as these salts are complex and non-volatile, with multiple ionisable functional groups, this requires a number of steps to achieve and so is not suited to ecological studies.

This new paper, from Udaya Nasini and colleagues at the University of Arkansas at Little Rock, US, proposes using liquid chromatography-mass spectrometry (LC-MS), and ionising the samples using electrospray ionisation. This has the advantage of being quick and simple (basically, the samples are mixed with methanol, stirred then filtered), and proved to be very reproducible, even with three-month-old frozen turds.

Using their technique, they evaluated the bile acid profiles of a number of wild animals, including mountain lion, black bear, bobcat, coyote, fox and puma, noting significant differences between them. To further test their methods, they received ‘blinded’ samples from Little Rock Zoo, and correctly identified them.

They conclude with the usual further research is needed comments, and clearly their selection of species is based on the stools they might find nearby, but for mountain lions at least, they do say that ‘this method appears to be better and more reliable than those available or in use at present’. With the rapid reduction in both size and cost of MS devices, this technique could become a standard trick for coprophilic ecologists world over.

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Species-specific signatures in scat, 9.6 out of 10 based on 5 ratings
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