Territorial Behavior and Social Stability in the Mouse Require Correct Expression of Imprinted .

Genomic imprinting, the epigenetic process by which transcription occurs from a single parental allele, is believed to influence social behaviors in mammals. An important social behavior is group living, which is enriched in Eutherian mammals relative to monotremes and marsupials. Group living facilitates resource acquisition, defense of territory and co-care of young, but requires a stable social group with complex inter-individual relationships. Co-occurring with increased group living in Eutherians is an increase in the number of imprinted loci, including that spanning the maternally expressed . Using a 'loss-of-imprinting' model of (), we demonstrated that twofold over expression of results in abnormal social behaviors. Although, our previous work indicated that male mice were more dominant as measured by tube test encounters with unfamiliar wild-type (WT) males. Building upon this work, using more ecologically relevant assessments of social dominance, indicated that within their normal social group, mice did not occupy higher ranking positions. Nevertheless, we find that presence of animals within a group leads to instability of the normal social hierarchy, as indicated by greater variability in social rank within the group over time and an increase in territorial behavior in WT cage-mates. Consequently, these abnormal behaviors led to an increased incidence of fighting and wounding within the group. Taken together these data indicate that normal expression of is required for maintaining stability of the social group and suggests that the acquisition of monoallelic expression of may have enhanced social behavior in Eutherian mammals to facilitate group living.