Mice and Predator Urine: Familiarity Breeds Danger

In a possible argument against keeping one's enemies close, at least if one is a rodent, researchers at Russia's A. N. Severtsov Institute of Ecology and Evolution say that mice exposed to cat urine early in life will not fear it later, and are more likely to be caught. The research was presented at the Society for Experimental Biology 2015 meeting in Prague this week.

"Because the young mice (less than two weeks old) are being fed milk while being exposed to the odor, they experience positive reinforcement," Dr. Vera Voznessenskaya, a researcher at Russia's A. N. Severtsov Institute of Ecology and Evolution, said in a press release. "So they don't escape the cats when exposed to cat odor later on."

At the same time, the researchers say the mice are influenced not just by the milk, but by a certain molecule, L-Felinine, in cat urine. According to previous research led by Voznessenskaya and published in 2014 in the journal Neurobiology of Chemical Communication, the molecule influences mice reproduction -- lowering a female's ability to get pregnant and minimizing litter sizes.

Interestingly, while the mice may not realize they should escape the cats later in life, they still experience elevated hormone levels (corticosterone) in reaction to the cats, Voznessenskaya said, in a release