Macho Males Smell Better, at Least to Female Mice

Male dominance isn’t just about beating the competition to a pulp: When a male house mouse conquers new territory, it releases come-hither pheromones

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File photo: Mr. Universe Leo Robert and his son Norman, 1955.
File photo: Mr. Universe Leo Robert and his son Norman, 1955.Credit: Alan Oxley /Hulton Archive / Ge

Machismo, an ephemeral concept — or is it? Ten to one, somebody reading this will invent a men’s cologne with the aroma of mouse balls, though if they finish the story they might finesse the source of the idea.

The story is that male dominance isn’t just about beating the competition, then one’s hairy chest, then impregnating the lady. It turns out that macho males smell better to females, say Viennese researchers, having checked the matter in mice.

In mice, machismo is measurable by dominance. The study from Vetmeduni, the University of Veterinary Medicine, Vienna, shows that female house mice in heat are attracted to the scent of dominant males more than to the scent of the more retiring sort. When the female mice weren’t in heat, they couldn’t care less how the male smelled, by the way, the team reported in Nature on Friday.

The team, led by Dustin Penn, also demonstrated that dominant male mice produce higher levels of certain pheromones than subordinate males.

Dominant mice smell betterCredit: © K. Thonhauser/Vetmeduni Vienn

Pheromones are a primordial method of sexual signaling. They cause all kinds of biological cascades, and may go back to near the dawn of life. These chemicals exist in all animals, from fish to lizards, where their function was demonstrated in skinks and crocodiles, for instance, to insects.

While the universal existence of pheromones has been proved, this study sheds fresh light on their role in sexuality. It isn’t just that dominant male mice beat off the other males and conquer the female. It seems that even if she hasn’t been reading Harlequin romances, as mice do, she would like him to, because the macho male smells better to her.

“Male house mice produce several pheromones, which are volatile and non-volatile chemical signals that have potent effects on the reproductive physiology and behavior of females,” the team explains.

Where do female mice encounter the macho miasma? Mice are territorial. Like, say, cats, they mark their territories with urine — and the pee of male mice that conquered a territory turns out to have more than double the excretion of certain proteins, some of which are pheromones, and some of which cause the release of pheromones.

As Penn explains: “We also conducted olfactory tests and found that sexually receptive female mice were more attracted by the scent of dominant than subordinate males, whereas non-receptive females did not show this olfactory preference... This finding is a fascinating example of how changes in social behavior can affect gene expression.”

When the research team delved into the biochemical aspect, they found that dominant male mice were producing, among other things, more of a volatile pheromone that attracts females and influences their reproductive physiology.

Finally, the scientists wondered why the females would be attracted to macho males. “Since social status of male house mice is influenced by phenotypic and genetic quality (e.g., inbreeding), these findings suggest that [major urinary protein] excretion may provide a reliable indicator of the quality of potential mates,” they wrote. In other words, females don’t feel biologically attracted to the shrinking violets, but to the ones likely to survive better. If they can find a mouse that beats its hairy chest too, the race is over.