Fostering house mice onto rats and deer mice: effects on response to species odors

Newborn wild house mice (Mus musculus) were fostered upon maternal conspecifics, prairie deer mice (Peromyscus maniculatus bairdi) or laboratory rats (Rattus norvegicus). Male subjects were weaned into individual cages, in which they remained until testing commenced. At 35 days of age, subjects were given a four-choice test in which they had the opportunity to investigate tunnels scented with clean wood chips or with chips soiled by an adult male conspecific, deer mouse or rat. Compared to the Mus-nursed and Peromyscus-nursed mice, Rattus-nursed mice were more active during the test and less reluctant to investigate the Rattus-scented tunnel. These results were replicated in a two-choice test (Mus- vs. Rattus-scented tunnels) that included a group of mice fostered onto conspecifics, but with Rattus scents present in the maternity cage throughout the nursing period. Early exposure to the scent of Rattus had no significant effects on the responses of Mus-nursed mice to the scent of Rattus.