If a mouse Zuckerberg were to craft a social network, he could do worse than to build his Facebook out of pee. Mice use urine the way we use status updates - not only as markers that indicate identity, kinship and sex, but also as signals that give passersby a sense of what's going on vis-a-vis health, social dominance and babies.
Two molecular experts at the University of Parma, Italy, recently dove into the world of mouse pee signals, which are primarily made up of little barrel-like molecules called major urinary proteins. Or, more charmingly, MUPs.
MUPs aren't simply an aromatic blend of molecules. They're much closer to a communication system than to a Yankee Candle or bowl of potpourri. Depending on the way these MUPs are mixed together, mice are able to achieve a sort of pee-based grammar, the Italian scientists write in the journal Animal Behaviour. A MUP's shape - as well as any attached pheromones - dictate its meaning. Creating and sensing MUPs engage a set of organs all over the rodent body: the brain, the liver, the nose, the bladder and a host of glands.
Mice aren't shy about communicating with their urine. To hear writer Lisa Margonelli at Pacific Standard say it, there's no escaping the reach of mouse pee: "Most of our homes are soaked in mouse urine," with evidence of mice pee in four-fifths of American houses.
Spreading MUPs into the environment also comes at a cost to the mouse. As the researchers point out: "Voiding a huge amount of proteins ... should be a waste of nitrogen and energy." The scent of pee, likewise, can also alert predators to a mousey presence. But considering the information MUPs convey between mice, these smelly status updates are worth the risk.