Tracking Wildlife With Chromatography

The population of mountain lions, also known as cougars, in the eastern U.S. is thought to have fallen in recent years. To test whether the animals could be on the rebound, biologist Gary Heidt, chemist Ali U. Shaikh, and graduate student Jennifer Shirley at the University of Arkansas, Little Rock, are trying to develop chromatography and mass spectrometry methods to identify mountain lions by the bile acid profiles in their scat. Shaikh described their progress at a poster session organized by the Division of Analytical Chemistry at the American Chemical Society's national meeting being held this week in Boston.

Conservation biologists typically estimate mountain lion populations from the amount of mountain lion scat found in a particular region. People originally used the scat's size and shape, at best an extremely qualitative method, to determine whether it came from a mountain lion. Profiling the DNA present in scat is another option, but it's difficult to distinguish the predator's DNA from that of its prey. Heidt and Shaikh turned to bile acid profiles instead.

A variety of bile acids are produced by the liver and used by the intestines to aid in digestion by emulsifying food. The bile acid profile in an animal???s waste depends on the animal itself and the microbes in its gut. These complicated bile acid profiles might help distinguish mountain lions from other wildlife, Shaikh and his colleagues reasoned.

The team started with gas chromatography methods coupled with mass spectrometry. To make the bile acids amenable to GC analysis, the researchers derivatized the bile acids with trimethylsilyl or diazomethane. But these derivatization methods are time-consuming, and diazomethane is potentially explosive, so they turned to liquid chromatography paired with MS instead. The LC method allows them to separate bile acids that are not separated by the GC method. With this method, "we can really extract information about these bile acids even though they???re not very well resolved in the GC," Shaikh said. He and his colleagues are still developing the LC method to distinguish between some isomeric bile acids.

The scientists have not yet identified a bile acid unique to mountain lions that can serve as a marker. From the GC analysis, they had thought that glycocholic acid could be such a marker, but the LC analysis—with its better resolution and lower detection limits—revealed glycocholic acid in the bile acid profiles of other species. The researchers are continuing to search for an appropriate marker, Shaikh said. "There's a lot more work to be done.