For Mice, the Smell of Urine Is Sexy
The smell of urine may be attractive to female mice when choosing a partner.
Credit: Kerstin Thonhauser / Vetmeduni Vienna

There might be a link between fatherhood and urine spraying for mice. 

In a new study, researchers found that male house mice that surpass their peers at marking their territory tend to have more offspring.

Many animals use scent marking as a form of communication, from elephants and dogs to fish and crustaceans. Male giant pandas even spray their urine while in a handstand to reach the widest odor field. An animal's pee can convey a host of information to a potential mate or rival, including social dominance, sexual receptivity and health.

This is true for mice, too. Researchers had observed that dominant males marked their territory more than their subordinate peers. For the new study, a team in Austria set out to investigate whether a male mouse's scent-marking success enhances its reproductive success (i.e., how many babies it has). The researchers found that, yes, it does. [7 Ways Animals Are Like Humans]

"Our study provides the first direct evidence that scent marking is maintained by sexual selection, as it enhanced males' reproductive success when females could choose their mates," study researcher Dustin Penn, of the University of Veterinary Medicine in Vienna, explained in a statement.

In their experiments, Penn and colleagues collected the male mice's urine on PVC tiles in the animals' individual compartments. The team then simulated territorial intrusion by swapping tiles in the enclosures. Males generally ramped up their scent marking when they perceived a competitor in their territory, the researchers found.

In a second part of the experiment, the scientists let female mice choose to interact and mate with either or both of two unrelated males, each in their own territory. 

Let's just be friends

To check on the reproductive success of the mice, the researchers performed paternity tests on the babies born throughout the course of the study. The researchers also observed the social interactions of the mice each day.

While male mice that were better scent-markers produced more offspring, surprisingly, the team found that female mice were more likely to socialize with the less flashy males that had less scent-marking success.

The researchers speculate that perhaps the females, by doing so, were trying to incite male-on-male competition. The scientists wrote that their findings emphasize that female social preferences don't necessarily reflect their mating preferences.

The researchers say they are investigating the biochemistry of mouse urine to get a closer look at the communication signals it contains.

The research is detailed in the November issue of the journal Animal Behaviour.

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