In the ongoing cat-and-mouse game of feline hunter versus rodent prey, cats have evolved chemical warfare using their own urine to improve their hunting success, scientists have found.

Mice exposed to the smell cat urine early in their life are less likely to be aware of the same odor later in life, and thus less likely to successfully escape when stalked by a cat, Russian researchers are reporting.

Scientists from the AN Severtov Institute of Ecology and Evolution in Moscow have reported their findings in Prague ad the annual meeting of the Society of Experimental Biology.

They say they've identified a molecule in cat urine, dubbed L-Felinine, which has a number of physiological effect on mice.

"We already knew that odor affects reproduction in mice: in fact, this molecule (L-Felinine) is capable of blocking pregnancy in females and reducing the size of the litter," says lead researcher Vera Voznessenskaya.

After birth the molecule can still affect the mice, resulting in an effect that will not serve them will later in life when a cat is on the prowl for dinner, she says.

"Because the young mice (less than 2 weeks old) are being fed milk while being exposed to the odor, they experience positive reinforcement," she explains. "So they don't escape the cats when exposed to cat odor later on."

Mice who grow up around the unmistakable odor of cat urine are less likely to display signs of fear or to flee when they encounter the odor as adults, the researchers, even though their physical sensitivity to it is increased by their youthful exposure.

Although seemingly a negative, it may be an evolutionary adaption on the part of the mice that has a beneficial element, Voznessenskays says.

"You get a higher response, but less behavior," she says, "and habituating like this is probably useful for the mice; they can't run away, because they need to live around humans and food. And cats [also] live around humans."

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