Abstract and Summary

To assess the influence of “littermate” characteristics on early social interactions, preweaning spiny mice (Acomys cahirinus) were raised in pairs consisting of pups differing in age by 15 days, or with a Mus musculus agemate. Whereas the older pups appeared to be relatively unaffected by the replacement of their original littermate with a younger pup, the frequencies of suckling and social contact by the younger pups differed as a function of the age of littermates with whom they were raised. Likewise, although the behaviour of Acomys pups raised with conspecifics vs. Mus agemates did not vary, Mus pups housed with a Mus littermate displayed more frequent interactions with their littermate and less contact with the foster mother than did Mus pups raised with an Acomys littermate. It was concluded that the effective preweaning social environment of Mus and A. cahirinus consists of more than the mother. In particular, littermate characteristics appear to influence interactions between the pups themselves as well as with other social partners.