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.