When Female Mice Are Pregnant, They Expel Banana-scented Urine To Discourage Males.

Female mice who are pregnant or breastfeeding emit a banana-scented material in their urine, which is thought to stress males and prevent infanticide.

Male mice’s stress levels were examined when they were placed in the same cage as another male mouse or a female that was either not pregnant, newly pregnant, significantly pregnant, had recently given birth and was breastfeeding, or had already given birth and were no longer lactating.

When male mice were confined near female mice who were highly pregnant or nursing, they showed diminished pain sensitivity and raised corticosteroid levels, both of which are symptoms of stress, but not when they were caged near the other animals.

The researchers determined that this was due to extremely pregnant and nursing females producing a substance called amyl acetate in their urine, which smelled like bananas. When the men sniffed it, it floated into their cages and stressed them out.

Females probably emit this chemical to alert males when they are going to have pups or have recently had them. This is due to male mice attempting to murder pups fathered by other males.

In keeping with this, pregnant and breastfeeding females produced more urine markings when exposed to stranger males than when exposed to their pups’ fathers.