Nonapeptide mechanisms of social cognition, behavior and species-specific social systems

Nonapeptide functions have been explored in a diverse literature that has burgeoned in recent years, particularly in relation to affiliation, bonding and human social cognition. However, brain distributions of the oxytocin-like and vasopressin-like peptides are fundamentally similar across all vertebrate animals, including many species that do not exhibit social bonds, grouping, or even parent-offspring interaction. Hence, unifying principles extend beyond, and may even constrain, nonapeptide effects on social cognition and behavior. Conversely, nonapeptide receptor distributions are highly species-specific, suggesting almost limitless functional variation. Drawing on the vast recent literature, we here present a phylogenetically integrated review of both ubiquitous vertebrate features and species diversity, highlighting important nonapeptide effects on socially relevant physiology, sensorimotor integration, assignment of valence, and functional connectivity.