Asking weird questions is an essential part of being a science writer. The sort of stuff that stops dinner conversations cold or makes listeners respond “You really are a nerd, aren’t you?” It’s almost hopeless trying to defend oneself in these situations: “What? Who hasn’t wondered about what happened in the digestive system of Tyrannosaurus?”

The question that kept rattling around my skull this morning was “Why does maned wolf pee smell like marijuana?” This isn’t one of those “Why is a raven like a writing desk?” riddles. Maned wolves – large, South American canids that look like leggy foxes but are neither foxes nor wolves – spray very pungent, distinctive urine that smells akin to hops or cannabis. The aromatic resemblance is so close that police were once called to the Rotterdam Zoo in the Netherlands to search out a pot smoker, only to find that whoever made the report had been fooled by the scent of maned wolf urine.

I caught a whiff of maned wolf while visiting the Smithsonian’s National Zoo one spring morning last year. It wasn’t unpleasant – a slightly sweet, but stale and herblike scent. But why did it smell that way? What was the reason behind the strange convergence in odor?

As with other dogs, pee is an important part of a maned wolf’s communicative repertoire. A well-placed urine or scat signpost provides a wealth of information about an individual maned wolf. They are not social canids – they don’t hunt in packs, and males and females are typically only together for a short time from mating to shortly after the birth of the pups – but they still use their distinctive urine to mark their territory and find each other during the breeding season. In his 1984 report on maned wolves in the wild, zoologist James Dietz hypothesized that the particularly strong smell of their urine might be an adaptation to maintaining territories by being strong enough to be detected at a distance or long after the olfactory marker had originally been laid down.

Perhaps Dietz was right – extra-pungent pee would be advantageous to a territorial, solitary animal – but his hypothesis didn’t satisfy my curiosity. The idea potentially explained why maned wolf pee is stronger than cheap cologne, but not how it acquired its peculiar scent. I needed observations at a finer scale, and, fortunately for me, someone had already undertaken the dirty work of analyzing the chemistry of the canid’s extra-strength piss.

In 2005, Sara Childs-Sanford presented her master’s thesis “The Captive Maned Wolf (Chrysocyon brachyurus): Nutritional Considerations With Emphasis on Management of Cystinuria” to the faculty of the University of Maryland. The aim of her research was to improve the nutrition of maned wolves kept in zoos as a way to decrease the incidence of stones in the urinary tract, a widespread and often fatal malady among the captive animals. The problem appeared to be a buildup of cystine, an amino acid that crystallizes and creates blockages as urine becomes more acidic. In order to determine how changes in diet might make the wolf urine less acidic and decrease the opportunity of cystine to crystallize, Childs-Sanford had to analyze a lot of pee, and she took the opportunity to see if the secret behind the canid’s scent could be identified.

Based upon what was known about organic compounds in the urine and feces of cats and dogs, Childs-Sanford thought a sulfur-based compound was a possible culprit. Cats, for example, have a sulfur-containing amino acid named felinine in their urine which is involved in scent communication, so it seemed possible that maned wolves had something similar. This isn’t what Childs-Sanford found. Instead of an amino acid containing sulfur, she discovered that maned wolf urine was unique among carnivorans in having high levels of 2,5-dimethylpyrazine – an organic compound belonging to a group used in scent and chemical communication by many organisms and simply called pyrazines.

Pyrazines are curious because they often create strong odors that act as warnings. Insects adapted to display bright warning coloration also use pyrazines, as do toxic plants like milkweeds. “The role of pyrazines for this purpose may correlate well with the normal social behavior of the maned wolf,” Childs-Sanford suggested, proposing that the high pyrazine levels in maned wolf urine acted as a prominent and long-lasting sign that a given patch of territory has already been already spoken for. The peculiar, marijuana-smoke smell of the canid’s urine is an olfactory “Keep Out!” sign.

Should you visit a zoo that keeps maned wolves, be sure to stop and smell the pyrazine.

Top Image: A maned wolf (Chrysocyon brachyurus). Image from Flickr user Caroline.

References:

Childs-Sanford, S. (2005). THE CAPTIVE MANED WOLF (Chrysocyon brachyurus): NUTRITIONAL CONSIDERATIONS WITH EMPHASIS ON MANAGEMENT OF CYSTINURIA Master's Thesis: University of Maryland, College Park, 1-163

Dietz, J. (1984). Ecology and Social Organization of the Maned Wolf (Chrysocyon brachyurus) Smithsonian Contributions to Zoology (392), 1-51 [PDF Link]