Selectivity and Sociality: Aggression and Affiliation Shape Vole Social Relationships

Abstract

The formation of selective social relationships is not a requirement of group living; sociality can be supported by motivation for social interaction in the absence of preferences for specific individuals, and by tolerance in place of social motivation. For species that form selective social relationships, these can be maintained by preference for familiar partners, as well as by avoidance of or aggression toward individuals outside of the social bond. In this review, we explore the roles that aggression, motivation, and tolerance play in the maintenance of selective affiliation. We focus on prairie voles (Microtus ochrogaster) and meadow voles (Microtus pennsylvanicus) as rodent species that both exhibit the unusual tendency to form selective social relationships, but differ with regard to mating system. These species provide an opportunity to investigate the mechanisms that underlie social relationships, and to compare mechanisms supporting pair bonds with mates and same-sex peer relationships. We then relate this to the role of aggression in group composition in a comparative context.

Keywords: affiliation; aggression; meadow vole (Microtus pennsylvanicus); prairie vole (Microtus ochrogaster); selectivity; social motivation; tolerance.

FIGURE 1

Together with affiliation, aggression shapes the presence and nature of social groups. The vast majority of rodents are solitary, such as the Syrian hamster. Differences in the amount or extent of aggression (x-axis) shape group formation, with low aggression and territoriality promoting gregarious group structures (e.g., mice, rats, and spiny mice) that may be flexible in size and composition. The generality vs. specificity (y-axis) of how aggression is targeted shapes the selectivity of groups for specific known members. Selectivity may be maintained by “prosocial” factors such as motivation for social bonds, as well as by lack of aggression and intolerance toward group members vs. strangers. Highly selective species such as prairie voles exhibit both high levels of affiliation and stranger aggression, while less selective groups such as winter-phenotype meadow voles show preference for familiar individuals in the absence of social motivation or intense aggression. Photo credits: solitary rodent (Syrian hamster; The Rohit CC-BY NC 2.0), gregarious groups (Mice; Pixabay user Kapa65; Spiny mice; Aubrey Kelly by permission), selective groups (meadow voles and prairie voles; Beery Lab).