Scientists recently discovered something about male mice that is absolutely bananas: the distinctive smell of a banana stresses them out.
Researchers at McGill University in Montreal, Quebec, learned of this unusual aversion to fruit when they analyzed rising stress hormones in male mice when the males were around pregnant or lactating females. The scientists reported in a new study that the males’ hormonal changes were triggered by the presence of a compound called N-pentyl acetate in the females’ urine. It’s also the compound that gives bananas their distinctive smell.
“It all came as a surprise because we weren’t specifically looking for it and found it by accident,” said Jeffrey Mogil, senior author of the study and professor in the Department of Psychology at McGill University. “The pregnant females were in our lab for another experiment, and one of our students noticed that the males started acting weird,” Mogil told Live Science.
In the paper, the researchers wrote that “male mice, particularly virgin males, are known to engage in infanticidal aggression to improve their genetic fitness.” To keep these potential predators at bay, pregnant and lactating females rely on chemosignals, or sending chemical reactions through their bodies, to send messages to the males to stay away from their offspring.
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“Rodents and many mammals other than humans rely on their sense of smell,” Mogil said. “The odor mark in urine is well known, but what we found here is a new message that has never been described in mammals before. We’ve seen many olfactory messages sent from males to females, but there are fewer examples of females sending them to males. Most of these messages are related to sexual behavior, but in this case, sex has nothing to do with it at all. The women tell the men to stay away or else be prepared I’ll smack you if you touch my puppies.”
After observing that men’s stress levels increased in response to chemicals in women’s urine, Mogil and his team wondered if N-pentyl acetate from another source would elicit a similar response. They bought banana oil at a local supermarket and added the liquid to cotton balls, which they then placed in the cages of male mice. The presence of the smell measurably increased the males’ stress levels – just as the urine had done in previous experiments – and the researchers suspect that this hormonal spike is directly related to the stress one feels when faced with a potential fight.
Exposure to urine or banana oil also had an analgesic or pain-relieving effect and reduced the men’s sensitivity to pain, the study authors reported. Measured over time, the researchers found that pain resistance in the male mice developed as early as five minutes after smelling n-pentyl acetate and decreased 60 minutes after smelling it.
The study authors also discovered that the level of stress-induced analgesia was significantly higher in virgin male mice, suggesting that unrelated males posed a greater threat to pup survival than the fathers. The findings offer a glimpse into the invisible communication channels animals use to talk to each other, Mogil told Live Science.
“Mammals signal each other more messages than we originally thought,” he said. “We find that their communication is much richer than we give them credit for.”
The results were published in the journal on May 20 scientific advances.
Originally published on Live Science.
https://www.livescience.com/mice-fear-bananas Male mice are terrified of bananas. Here’s why.