Female mice who mate for life seem to take longer to get over the loss of their partner than male mice. The females are slower to begin a sexual relationship with a new partner – perhaps because life experience has taught them to be sceptical that a new male will stick around and help care for pups.
California mice (Peromyscus californicus) are monogamous rodents that form lifelong relationships with a partner, sharing a home and parenting duties. But if the partner dies or disappears, the bereaved mouse often finds a new life partner and reproduces.
Amber Valentino at Saint Joseph’s University in Pennsylvania and her colleagues discovered that this process happens more quickly if the bereaved mouse is male. A bereaved female might be “choosier” and so take longer to find a new partner, says Valentino.
The scientists speculate that this may be because the loss of a first mate leaves a female questioning the reliability of a new one.
“They need that extra paternal component, a male who will be there and who will actively engage in the successful rearing of offspring,” says Valentino. “So we suspect their decision to go ahead and have pups with another male takes longer based on the previous experiences they have faced.”
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Valentino and her colleagues examined the birth records of 59 California mice couples in their laboratories in which one was a virgin and the other had lost a partner within the preceding 24 hours (usually because the partner mouse had died of natural causes).
The team found that approximately 85 per cent of these mice couples had a litter of pups. This is about the same success rate as the researchers reported from a connected experiment involving 525 virgin-virgin mouse couples, says Valentino.
However, the pups typically came sooner when it was the male getting a new partner, she says. In fact, bereaved males entered a sexual relationship with a virgin female just as fast as they did with their first partner, with pups being born on average 55 days after the first meeting.
When it was a bereaved female mouse being offered a virgin partner, though, pups were born on average 65 days after the adult mice first met. This indicates that the females took about 10 days to decide to accept the new mate and enter a sexual relationship.
The scientists think females wait longer than males because their reproductive investment is greater, through pregnancy and nursing, and because of the price they pay for an absent father. Previous research suggests there is up to a 35 per cent reduction in pup survival when the father goes missing, says Valentino.
“Females need that extra paternal component to help make sure that offspring and reproduction will actually be successful,” she says.
Journal reference: Behavioural Processes, DOI: 10.1016/j.beproc.2021.104415