Title: Behavioral, physiological, and neurobiological plasticity of mice living in social hierarchies
Description: The ability to modulate behavior and physiology when encountering novel social contexts is essential for the survival and fitness of socially living species. During social interactions, individuals must assess their current social environment and integrate this information with their own internal state and past social experiences to facilitate appropriate social behavior. This process leads to adaptive modulation of behavior and physiology. The behavioral dynamicswithin social dominance hierarchies are an exemplar of how individuals adaptively modulate theirsocial behaviors and physiology. However, much remains unknown about the behavioral, physiological, and neurobiological underpinnings of plasticity among individuals living in social hierarchies within complex social environments. This dissertation is composed of several studies aimed at investigating the behavioral and physiological plasticity and associated neurobiological characteristics of group-living mice as they form stable and consistent social relationships with unfamiliar social partners to achieve a social hierarchy.

In Chapter 2, I analyze how the patterns of both aggressive and non-aggressive social behaviors change as unfamiliar male mice establish social relationships in dyads, providing new statistical methods to define the resolution of a dominance relationship. In Chapter 3, I use an ethologically relevant experimental paradigm to investigate social hierarchies in large groups and explore how mice change their urination pattern (scent-marking) and metabolic investment in major urinary proteins as they acquire dominance status. In Chapter 4, I demonstrate the association between individual social ranks and foraging dynamics of mice living in social hierarchies. Collectively, the results of these studies suggest thatmaintaining high social status, particularly alpha status, can be energetically costly. Investment byalpha males in reproduction and territorial defense may come at the cost of resources available topromote long-term health, particularly responses to immune challenges. To explore thishypothesized trade-off, inChapter 5, I test the hypothesis that individuals of different socialstatus vary significantly in immune system functioning.

I demonstrate that dominant males are primed to utilize adaptive immunity while subordinate males invest more in innate immunity. In Chapter 6, I explore the neurobiological characteristics of social dominance, with a particular focus on the association between the oxytocin and vasopressin neuropeptide systems and social status. I idenfity several brain regions, such as nucleus accumbens and lateral preoptic area, inwhich alpha, subdominant and subordinate mice show significant differences in the levels ofoxytocin receptors and vasopressin 1a receptors. To better understand how the brain responds to social cues, in Chapter 7, I identify brain regions in dominant and subordinate mice that respond to cues regarding social status and familiarity. I demonstrate that brain regions in the social decision-making network respond distinctively depending on the social cue types sensory information and the internal state. Finally, in Chapter 8, I explore brain transcriptomic profiles associated with behavioral differences among alpha, subdominant, and subordinate male mice.

Overall, this dissertation contributes significantly to our understanding of how an individual’s social context leads to plastic and adaptive changes in the brain, behavior and physiology.