A male slithers into a bar looking for a date. He spies a female surrounded by three suitors. What should he do?
Well, if he's a red-spotted newt, he'll back off in a hurry. This common salamander knows when there's too much competition, and three seems to be the magic number. But it's not arithmetic that the newt goes by; rather, he's sniffing an antimale pheromone produced by the competition, Daesik Park of Northern Arizona University in Flagstaff reported last week at the annual meeting of the Society for Integrative and Comparative Biology in Atlanta.
Although some insects are known to emit odors repellent only to males, no such substance in a vertebrate had ever been described, Park says. But his team thought newts might be armed as such because the pond dwellers are known to exude odors for use as long-distant lures and short-distance seducers. Besides, the males need all the help they can get in fathering offspring: They outnumber the females in breeding ponds.
With Northern Arizona reproductive endocrinologist Catherine Propper, Park a graduate student, used a Y-shaped chamber to test whether a male would approach a new newt couple. He found that the lovelorn male is just as likely to go for a female consorting with one or two males in one arm of the Y as he is to choose one on her own in the other arm. But if a female has three suitors, the stag newt will usually opt for the lone female. In other tests, Park found that a male close to a female emits a repelling compound into the water. The more courting males, the more potent the smell--to the point where three stinkpots will put off an aspiring newcomer, Park suggested.
The work "provides us with one more mechanism by which males may compete with other males to enhance their reproductive success," says David Pfennig of the University of North Carolina, Chapel Hill. As Park observed, if a newt decides to hit on a perhaps less desirable but more available female, "the reproductive success of both the pheromone-releasing and -receiving males may be increased."