(ORDO NEWS) — Analyzing the release of stress hormones in male mice, the researchers found something strange: the stress response in the test subjects was caused by… the smell of bananas.
It turned out that the characteristic smell of these fruits is given by the same substance that is contained in the urine of pregnant and lactating females, who are forced to scare away male mice in order to prevent them from eating helpless mice.
Smells play a huge role in the lives of most mammalian species, and laboratory mice are no exception. These animals, even while in neighboring cages, constantly exchange odor information, informing their relatives about their state of health, readiness for mating, and even, to some extent, about their mood.
The main smellers in rodents are males: they more actively mark the territory, signaling themselves not only to potential partners, but also to rival males.
Females in this respect are much more passive: it is enough for them to inform about their readiness to conceive offspring, after which the males themselves will figure out who is in charge here. Therefore, most often, scientists fix odor signals from males to females, but not vice versa.
Quite by accident, researchers from Canada discovered the odor signal that females send – and not just any, but only pregnant and lactating mothers. Note that infanticide , or the killing of cubs, is not alien to male mice. To protect offspring, mother mice have to aggressively defend them from males, and they do this, including through smell.
The urine of pregnant and lactating female mice contains n-pentyl acetate , an odorous organic substance reminiscent of ripe apples and bananas.
For a person, this smell is quite pleasant and does not cause negative associations, but for a male mouse, it means that somewhere nearby there is a nest of a female, which, upon detecting a stranger, will immediately rush into battle.
Not surprisingly, the smell of bananas (and even banana oil bought at the supermarket) males reacted by releasing stress hormones, thereby preparing for a possible collision.
Curiously, the most striking reaction to the smell of urine (or bananas) was observed in sexually inexperienced males (in other words, virgins), who, purely physically, could not be fathers of mice.
The researchers suggest that this is probably due to the greater threat posed by unrelated males: if the father can still calmly treat his offspring, then the stranger is likely to try to kill the cubs and re-mate with their mother.
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