Alloparental care in social muroid rodents

The article concerns fitness effects of alloparental care, or helping (i.e., assistance of young individuals in rearing offspring that are not their own) in social muroid rodents (Meriones unguiculatus, Mi-crotus ochrogaster, Microtus pinetorum, Lasiopodomys mandarinus, Peromyscus polionotus, and Rhabdomys pumilio) that are characterized by a family-group lifestyle and biparental care. According to inclusive fitness theory, alloparenting may alter both direct and indirect fitness. In particular, helpers may benefit indirectly if breeders that receive assistance subsequently produce more offspring. In laboratory studies, however, neither the presence of alloparents nor greater numbers of alloparents affected litter size at weaning. The results of the experimental studies also provide little support to the hypothesis that breeders benefit directly by increasing their lifetime reproductive success. In some species, helpers may decrease the workload of breeders, but the effects of alloparenting were found to be slight and often mixed. However, there is evidence that alloparental care yields direct benefits to helpers by providing experience that allow them to become more successful par-ents. It seems unlikely that helping behavior evolved merely to kin selection in consistence with 'Hamilton's rule'. A more appropriate explanation is that helping behavior in rodents is a by-product of the evolution of sociality, i.e. the transition to a family-group lifestyle with biparental care. Extended family groups with help-ers form due to delayed dispersal of offspring, and the latter may gain direct and/or indirect fitness benefits from staying within their natal groups. Alloparenting could be considered a form of cooperation due to which both breeding pairs and their older offspring being helpers may gain direct or indirect fitness benefits.