CORVALLIS, Ore. - University researchers have discovered one of the first pheromones in a vertebrate animal species that is produced by the male and helps him when courting a female, in this case making her more calm, receptive to mating and less apt to run away.
The study, to be reported Friday in the journal Science, was done with a species of terrestrial salamander called Plethodon jordani. But, as scientists learn more about this mysterious world of chemical communication, it seems likely that there may be many other pheromones that affect behavior and mating in many animal species, including humans.
"It's very unusual in nature to find a pheromone that male vertebrates use in courtship and mating," said Lynne Houck, an associate professor of zoology at Oregon State University and co-principal investigator on the study, along with colleagues at the University of Chicago and University of Louisville. "Usually you find these types of pheromones only in the female."
The researchers in this case identified the pheromone, a single protein component that affects the female, and the gene that is responsible for production of that protein. Of considerable interest, Houck said, is that this gene is similar, although not identical, to one found in humans.
In salamanders, the courtship and mating process is odd.
"Terrestrial salamanders aren't always wildly enthusiastic about mating, and there are only a few weeks or months of the year that the female will even consider the idea," Houck said. "And, during that time, the chances of her mating with a male are considerably reduced if he doesn't produce this particular pheromone."
In that process, one part of which is called a tail-straddling walk, the male deposits pheromones from a gland under his chin - a gland which only becomes active during mating times - onto the female's nose.
Repeated deposits of this chemical seem to soothe the female, make her more receptive to mating and also more inclined to do it quickly, speeding up a process that can take 45 minutes or more and expose both the animals to other dangers. And the process is discreet, not readily apparent to other salamanders who may wish to compete for a mate.
In an unusual reproductive process, the female salamander then stores the sperm deposited by this male and uses it at some point weeks or months after insemination to fertilize her eggs. The benefit of this time delay between mating and egg laying is that the female can search for a very secluded place that is just large enough for her and her eggs. The female will stay with her eggs for about four months, guarding them against predators.
Pheromones are increasingly being studied by researchers for the key roles they play in species recognition, reproduction and other behaviors. Pheromones have commonly been identified for many insects, but less so for vertebrate animal species.
However, Houck said, there is some clear evidence of their operation in humans. Research has shown that female humans who spend a great deal of time in one another's company often send out chemical signals that help them synchronize their menstrual cycles. And there's evidence that a woman who spends much time around a single man develops a more regular menstrual cycle, which might be conducive to successful conception.
"The sexuality of humans is obviously pretty complicated and goes far beyond a single chemical cue," Houck said. "But that doesn't preclude the possibility that in fact there are some chemical cues at work which we don't yet fully understand."