Early experience, reproductive success, and development of parental behaviour in Mongolian gerbils

Extended residence by non-breeding subadult 'helpers' within families or communal groups has traditionally been explained by the theory of inclusive fitness. However, the theory of inclusive fitness does not account for cases in which helpers do not promote the survival of siblings or in cases where helpers are unrelated or only distantly related to offspring. We investigated the hypothesis that Mongolian gerbils, Meriones unguiculatus, contribute to their individual fitness while living as non-breeders in their natal family group. Breeding pairs of gerbils were constituted so that the male, female, neither, or both members of the breeding pair received experience with younger siblings while in the natal group. Prior experience with younger siblings affected reproductive performance. Pairs in which males were experienced produced their first litter significantly sooner than pairs with inexperienced males. Pairs with at least one experienced member were also more likely to produce a litter within 50 days of pairing (16 of 26 pairs) than pairs in which neither member was experienced (one of seven pairs). Pups born to pairs with experienced males gained weight more rapidly and had earlier eye opening for the first litter than pups born to pairs with inexperienced males. Extended residence in breeding groups by non-breeders could contribute to individual reproductive success through enhanced breeding performance.