Project Summary The social environment has profound effects on organismal biology, including human health. Individuals vary in their physiological and behavioral responses to social stimuli, and this variation can manifest as difficulties in social perception, learning, and behavior in everyday life, or as increased risk for specific neuropsychiatric symptoms in response to social adversity. Previous work has focused predominantly on discovering the mechanisms of specific forms of social perception, learning, and behavior, but less attention has been devoted to understanding how these processes vary among individuals. This proposal leverages the strong genetic, neurobiological, and behavioral variation within prairie voles to investigate how integrated levels of biological organization generate individual variation in responses to social stimuli. Briefly, prairie voles exhibit a suite of unique social behaviors, including pair bonding, consoling, extensive alloparental and biparental care, and selective aggression toward opposite-sex conspecifics following pair bonding. These behaviors vary among individuals, and in some instances this behavioral variation has been linked to genetic and neuroendocrine variation, although the underlying molecular and cellular mechanisms are unknown. This proposal has three main objectives: 1) improve methods for measuring social behaviors in prairie voles; 2) identify cell populations that respond to specific forms of social stimuli; and 3) determine genetic and neuroendocrine factors underlying variation in cell type-specific and behavioral responses to social stimuli. These objectives will be accomplished by integrating behavioral analysis tools, genomics, single cell omics, spatial transcriptomics, and pharmacological manipulation in a powerful model for social behavioral variation. Completion of these projects will bridge knowledge gaps between genomics, neuroendocrinology, and circuit neuroscience; address untested models of social neural processing; and reveal specific genes, molecular systems, and cell populations underlying social behavioral variation.