An experimental test of kin association in the house mouse

Studies of genetic markers have suggested that female house mice (Mus muscu lus domesticus) prefer spatial association and nest sharing with close kin. Further, observations of mothers in single and communal nests suggest a po tential advantage of association with kin, namely, improved reproductive su ccess through cooperative defense of young against infanticide. In semi-nat ural enclosures, we tested for spatial association of female mice in small groups of sisters versus small groups of virtually unrelated females. We al so examined success in producing and weaning litters by sisters versus moth ers that were not close kin. Sisters exhibited greater spatial association than expected, although some groups of nonsisters showed close associations as well. All 14 sisters in the enclosures produced and weaned young in com munal nests. Among 15 mothers that did not have sisters available, 4 did no t produce litters, 2 shared a nest, and only 3 weaned young. Although infan ticide occurred for both kinds of mothers, it was significantly more common in the single nests of nonsister mothers than for sisters. Thus, sisters w ere more successful at weaning young, probably owing to advantages of commu nal nesting. These results suggest that close female kin may associate spat ially, and that there are distinct reproductive advantages due to the prese nce of close kin. The society of house mice is generally described as male dominated, but association of female kin may constitute the basis of social grouping in house mice.