Study shows that mice ‘eavesdrop’ on rats’ tears

In the animal kingdom of olfactory cues, smells signposting sex and danger tend to be the most potent. Sometimes, as a new study reveals, a scent can relate to both at the same time.

Research published today in Current Biology, shows that mice can “eavesdrop” on pheromones in the tears of rats trying to attract a mate, alerting the smaller animals that there’s a predator nearby. The study claims to be the first report of a prey eavesdropping on its predator’s pheromones.

Examining male rats, the researchers behind the study identified a compound in the rodents’ tear fluid, which they dub cystatin-related protein 1 (CRP1). This protein is picked up by female rats and, in what the study describes as “typical sexual behavior”, causes them to stop moving and assume a crouching posture.

Mice that “eavesdrop” on CRP1, however, interpret the signal very differently. Instead of setting off a sexual response, they pheromones activate a defensive circuit in the rodents’ brains, causing their heart rate and temperature to drop. Previous studies have found evidence of predators sniffing out their prey’s pheromones, but what’s unique about the finding is how the prey species has evolved to flag a predator’s sex pheromones.

“It has been known that in some combinations of predator and prey, such as between birds and insects, snakes and lizards, or weasels and voles, predators eavesdrop on the odorants of their prey so that predators can find and eat them,”  Kazushige Touhara, a professor at the University of Tokyo and lead researcher on the project, tells Alphr. “But our study is the first to report that prey eavesdrops on pheromones utilised in their predators, so that they can get alarm information before they get into trouble.”

The discovery opens a new way of thinking about the evolution of predator-prey communications, with a millenia-old dance around pheromones allowing mice and rats to “eavesdrop” on each other’s signals. The researchers plan to investigate this relationship further, examining the ways rats and mice read the other species’ body signals.

“This is the ‘game’ of animal kingdom or a kind of ‘trade’ or ‘diplomacy’ for both predators and preys to survive, which is acquired during the course of evolution,” says Touhara.