Pass (on) the Popcorn

Binturongs – also known as bearcats (but related to neither) – are elusive creatures from the forests in southeast Asia with a distinctive feature: their urine smells like buttered popcorn. Five researchers – Christine Drea (a professor in the Department of Evolutionary Anthropology at Duke University), Tom Goodwin (a distinguished professor of chemistry at Hendrix College), Anneke Moresco (a postdoctoral fellow at Cincinnati Zoo and Botanical Gardens), Lydia Greene (a graduate student at Duke) and Tim Wallen (an undergraduate student at Hendrix) – combined forces to find out why a mammal that works so hard to hide manages to smell so… appealing.

The researchers took samples of urine during standard medical examinations, and subsequently identified 29 chemical compounds – including the one responsible for the popcorn scent. “We found that 2-acetyl-1-pyrroline (2AP) was a major volatile compound emanating from both male and female binturong urine,” says Drea. Its correlation with the reproductive hormone, androstenedione, a precursor both of testosterone and of estrogen, led the team to conclude it may be a pheromone used to indicate that a binturong is in the vicinity. Furthermore, 2AP was among the few compounds that were resistant to decay and became more dominant over time – an advantage for solitary animals roaming through dense vegetation. “From the scent profile, other binturongs would be able to tell what sex the depositing animal is, how long ago it was there, and what reproductive state it might be in,” Drea says. In other words, key information for a binturong looking for an amorous encounter.

The team used solid phase dynamic extraction (SPDE) GC-MS (Agilent Technologies 6890N and 5973N). “These techniques can detect very small concentrations of each compound – and no chemicals or solvents have to be added, making it an environmentally benign method of analysis,” says Goodwin. “For most of the compounds we identified them with the NIST library. For 2-acetyl-1-pyrroline, however, we synthesized it using a literature procedure, and compared its mass spectrum and retention time to the peak from the binturong urine. The method was qualitative in the sense that we did not determine the exact concentration of each compounds.  We made qualitative comparisons of the peak areas in the mass spectral data.”

What isn’t clear is how the binturong produces 2AP. “If you were to make this compound, you would have to use temperatures above what most animals can achieve physiologically,” says Drea. After finding no trace in their food, the researchers believe the most likely explanation is that 2AP is produced when binturong urine comes into contact with bacteria and other microorganisms.

Drea’s own interest was sparked when she realized that the Carnivore Preservation Trust (CPT – now called the Carolina Tiger Rescue) was near Duke University – and by the fact that female binturongs were reputed to be dominant to the males. “I’m particularly interested in understanding ‘exceptional’ species in which females rule the roost, so I made a trip out there to have a look,” she says. “That’s when I met with Anneke (who was the main veterinarian at the time) and we devised a plan to study reproductive hormones.” Drea had already been collaborating with Goodwin, researching chemical communication in other species, a joint venture that allowed them to look at the links between reproductive hormones and volatile chemicals.

“They are solitary animals, but are great to work with,” says Moresco. “Everything we learned from their reproductive to nutritional habits was new in a sense, because there is so little known about them. Did you know they are one of only two carnivorous mammals with a prehensile tail? That’s important to take into account when trying to catch and handle them!”