C&EN: CRITTER CHEMISTRY - STINKY, YET SEXY

RACHEL SHEREMETA PEPLING, C&EN WASHINGTON

Ever smell a giraffe? To most people, they don't exactly smell like a bed of roses.


	EAU DE GIRAFFE Pungent scent may advertise a pest-free mate. DIGITAL VISION PHOTO

Early African explorers described the scent produced by giraffes as both "a hive of heather honey in September" and "a most disagree-able [sic], musky, nauseating odour [sic]," according to William F. Wood, organic chemistry professor at Humboldt State University in Arcata, Calif. Wood describes their scent as "fecal-like" when near the animals but more pleasant from farther away.

Wood attributes this smell dichotomy to the presence of indole and 3-methylindole (skatole). "At high concentrations, humans rate the two compounds as 'very stinky,' but at low concentrations they are rated as 'pleasant,' " Wood says. He also points out that indole is found in low concentrations in many flowers and is even used in some perfumes.

Wood and Paul J. Weldon, a researcher at the Smithsonian National Zoo's Conservation & Research Center in Front Royal, Va., recently identified these compounds as the source of the fetid scent produced by reticulated giraffes (Giraffa camelopardalis reticulata) [Biochem. Syst. Ecol., 30, 913 (2002)].

Wood has a nose for sniffing out skin gland secretions of vertebrates. Previous subjects include skunks, deer, antelope, and snakes. He got wind of giraffe odor after his coworker, Weldon, visited Silver Springs Wild Animal Park in Silver Springs, Fla. "On a chance that we might find something, he took a sample of the giraffes' hair," Wood says.

Samples from both male and female giraffes were taken from the back, shoulder, and neck in order to avoid contamination from urine or feces. Then, Wood and Weldon used gas chromatography-mass spectrometry to analyze dichloromethane extracts of the samples.

In addition to indole and 3-methylindole--the main causes of the giraffe's pungent odor--the researchers also found octane, benzaldehyde, heptanal, octanal, nonanal, p-cresol, tetradecanoic acid, hexadecanoic acid, and 3,5-androstadien-17-one.

Many of the compounds are antimicrobial and may afford giraffes protection from microorganisms and ectoparasitic arthropods. According to Wood and Weldon, the levels of p-cresol found in the samples are sufficient to repel some ticks.

Samples from male giraffes yielded higher levels of the odoriferous compounds than those from female giraffes. Wood believes that a strong odor may be just what the lady giraffes are looking for. "The fact that these compounds are highly odoriferous and antimicrobial will advertise that 'stinky' males will make better fathers," he says. "A strong odor would likely mean more offspring."

How giraffes produce their pungent compounds is not known. Wood suggests that oil and sweat glands in the skin are likely sources.

The antimicrobial compounds on giraffes could also work against microbes that commonly plague humans--such as Streptococcus mutans, a tooth-decay bacterial species, and Propionibacterium acnes, the human acne-causing bacteria--but don't expect to see products derived from giraffe compounds on store shelves. Wood says there are no plans to pursue human uses of the highly odoriferous compounds. "We think they stink!"