Pheromone cuts down a male's flirting time

Science News,  Sept 18, 1999  by S. Milius

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A male salamander doesn't exactly get his date tipsy to speed courtship to its standard conclusion.

However, there's just something about the scent of his chin that does the same job, and now researchers say they know what that enticing something is.

Earlier work suggested that a gland that appears under the chin of a male Jordan's salamander during breeding season produces a chemical message, or pheromone, explains Stephanie M. Rollmann of the University of Chicago. Entomologists have identified perhaps a thousand insect pheromones, but vertebrate chemistry has proved harder Counts differ, but the total of identified vertebrate pheromones is still struggling toward a dozen.

Rollmann and her colleagues propose a protein from the salamander's chin gland as the latest addition to the list. In the Sept. 17 SCIENCE, they report tracking down the scent's active component and sequencing its gene.

That sequence, they argue, resembles those for interleukin-6 cytokines, a diverse family of compounds regulating cell growth. "I was surprised," Rollmann says. This is the first hint of cytokines as pheromones.

The effect of the chemical also is "quite novel," comments John G. Vandenbergh of North Carolina State University in Raleigh. Mice, gerbils, black-tailed deer, and some antelopes--among other animals--use scents in courtship, usually as attractants, he says. However, he can't think of another vertebrate pheromone that influences the amount of flirting.

To demonstrate the effect, Rollmann and her colleagues purified a proton from the chin gland. They then removed chin glands of 11 male salamanders.

These males still courted normally, luring a female to perform an amphibian waltz in which she straddles his tail and the pair waddles forward. During this duet, lasting up to about an hour, "he'll curl back and slap his gland across the openings to her nose," Rollmann says. The pheromone molecule is too heavy to waft through the air so these little love pats normally deliver the proton.

When Rollmann dabbed females with the proton, nine pairs spent less time tail straddling than they did when Rollmann used a saline solution as a control. On average, she observed about a 15 percent reduction in flirting time.

"I'd really like to know how it increases the mating success of a male in the wild," remarks Ring T. Carde of the University of California, Riverside. Carde, who studies moth pheromones, acknowledges that tracing pheromone effects in vertebrates is "much, much harder" than in insects.

Bets Rasmussen of the Oregon Graduate Institute in Beaverton called the work "an exceptional study." The compound itself intrigues her, she says, because she sees growing evidence for proteins playing a role in vertebrate pheromone systems.

Vertebrates send and recede pheromones via many routes. The pheromone that Rasmussen discovered, which also turns out to be a component of many moth pheromones, appears in a female elephant's urine. Male red-sided garter snakes pick up a sexual signal when they flick their tongues across a female's skin. The other known amphibian pheromone, from an aquatic-breeding salamander, disperses in water.

Although it's too early to generalize much about vertebrate pheromones, the field "is in a very dynamic state right now," says Rasmussen.

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