Components of lifetime reproductive success in communally and solitarily nursing house mice — a laboratory study

Abstract

Under laboratory conditions, communal nursing among familiar and closely related female house mice (Mus domesticus) improved lifetime reproductive success compared to females rearing litters alone or females living with a previously unfamiliar, unrelated partner (reproductive success was measured within an experimental “lifespan” of 6 months, standardized as 120 days after mating at the age of about 2 months). An analysis of the contribution of three multiplicatively combined components to variation in reproductive success among breeding females revealed that, in all three social groups, survival of young until weaning contributed most to differences in lifetime reproduction (46–64% of the total variance). Females living with a sister had a significantly higher probability of reproducing successfully than females in the other groups, and also reared significantly more litters communally than females sharing nests with an unrelated partner. Weaning probabilities of young were highest in litters cared for by sisters and lowest in nests of unrelated females. Young were found dead either directly after birth (within the first 2 days of lactation) or after they had been cared for and nursed for at least 1 day. The loss of an entire litter typically occurred directly after birth. In monogamous females rearing litters alone the death of almost all young coincided with such early entire-litter mortality. In polygynous groups, however, offspring died at an older age and more litters suffered the loss of some young. Still, rearing young with a sister improved survival directly after birth and fewer litters were lost entirely in comparison with females in the other groups. In polygynous groups, pregnant females were observed to kill some of their partner's dependent young shortly before they gave birth themselves. As a consequence, individual young had reduced survival when they were firstborn in a communal nest (another litter was born within 16 days). Analyzed over a lifetime, communal care among familiar and closely related female house mice seems to be an adaptation to maximize the survival of offspring until weaning.