The Sikkim mouse ( Mus pahari ) exhibits distinct spatial, circadian, and social behaviors compared to laboratory mice

While the laboratory mouse is one of the most studied organisms on the planet, comparative research on the spatial and social structures of closely related Mus species remains limited. Here, we characterize the spatial, circadian, and social behavior of the Sikkim mouse ( Mus pahari ) wild-derived inbred strain PAH/Eij in comparison to the laboratory mouse strain C57BL/6J ( Mus musculus domesticus , shortened to ‘B6’). Using a common garden approach, we monitored mice in replicate mixed-sex group social behavior trials within an indoor mesocosm using radiofrequency identification (RFID) antennae. M. pahari exhibited markedly reduced spatial exploration and highly stereotyped circadian activity that was strongly coupled to the dark phase of the light-dark cycle compared to B6 mice. Most strikingly, M. pahari displayed distinctive social behaviors characterized by strong male-male gregariousness and enhanced overall social tolerance, contrasting sharply with the relatively less social nature of B6 mice. These results demonstrate the genetic influence on social organization within the Mus genus and identify unique socio-spatial phenotypes in M. pahari , highlighting the considerable potential of this strain and species as a novel model for social behavior research.