Sociability genetically separable from social hierarchy in amniotes

The emergence of social structure and organization is essential for the evolution of amniotes, including human beings. Sociability and social hierarchy are two key features to form a social group. However, it remains unknown whether sociability and social hierarchy are genetically separable. In this study, we examined the social hierarchy, social and social novelty preference of PAS1 (placental-accelerated sequence 1) knock-out and knock-in mice. PAS1 is a social enhancer that modulates social hierarchy. We found that PAS1 knock-out mice lack social hierarchy while wallaby/chicken PAS1 knock-in mice establish stable social ranks. Moreover, social and social novelty preference was observed in all PAS1-mutated mice. PAS1 knock-in mice have stronger preference to interact with other mice than wild-type mice (C57BL/6). No aggressive alteration was found in PAS1-mutated mice. Overall, our results showed that PAS1 is an indispensable regulatory element in the formation of social hierarchy while PAS1 regulates one of pathways modulating sociability. Therefore, sociability is genetically separable from social hierarchy in amniotes, providing insights into how social structure and organization evolved.