Stress in groups: Lessons from non-traditional rodent species and housing models

Abstract

A major feature of life in groups is that individuals experience social stressors of varying intensity and type. Social stress can have profound effects on health, social behavior, and ongoing relationships. Relationships can also buffer the experience of exogenous stressors. Social stress has most commonly been investigated in dyadic contexts in mice and rats that produce intense stress. Here we review findings from studies of diverse rodents and non-traditional group housing paradigms, focusing on laboratory studies of mice and rats housed in visible burrow systems, prairie and meadow voles, and mole-rats. We argue that the use of methods informed by the natural ecology of rodent species provides novel insights into the relationship between social stress, behavior and physiology. In particular, we describe how this ethologically inspired approach reveals how individuals vary in their experience of and response to social stress, and how ecological and social contexts impact the effects of stress. Social stress induces adaptive changes, as well as long-term disruptive effects on behavior and physiology.

Stress Varies Along the Social Density Continuum

“…Indeed, empirical and theoretical work portrays social stressors at typical social density as being net-positive for the individual when they are administered acutely, contributing positively to adaptive social dynamics (McEwen, 2000;McEwen and Wingfield, 2003;Korte et al, 2005). Social stress at typical densities is a well-studied subject that has been reviewed thoroughly and recently (Tamashiro et al, 2005;Beery et al, 2020). Briefly, animals in conspecific groups experience social stress in the context of interactions such as fighting, courtship, and territory defense.…”

“…When group housed, both male and female mice form social hierarchies (Van Den Berg et al, 2015;Varholick et al, 2019;Williamson et al, 2019), and topranking positions are associated with reduced plasma CORT, decreased initiation of aggression, and increased reception of aggression (Louch and Higginbotham, 1967;Williamson et al, 2019; but see cases where CORT in top-ranking positions does not differ from that of lower ranks: Schoech et al, 1997;Pravosudov et al, 2003;Poisbleau et al, 2005). Hierarchy formation is typically associated with increased stress for all members, which can be reduced after a hierarchy becomes established (Beery et al, 2020). Results of studies that find changes in stress under social isolation may be clarified by accounting for social rank of individuals.…”

“…Stressors in this category are often regular occurrences in the lives of animals, and they have the ability to adaptively guide behavioral development. However, when allostatic load, the strain on the body due to the physiological response to stress (McEwen and Stellar, 1993), is chronically high, such stressors can inflict severe and persistent abnormal behavioral syndromes (McEwen, 2000;McEwen and Wingfield, 2003;Tamashiro et al, 2005;Beery et al, 2020). Through allostasis, such social stressors together contribute to an overall increase in fitness, keeping an individual on track for success in its social environment (McEwen, 2000;Korte et al, 2005).…”

The Contribution of Environmental Enrichment to Phenotypic Variation in Mice and Rats

“…While this can serve to increase social enrichment, its implementation must also keep the needs of each species and sex in mind. For example, issues of social hierarchy and dominance are more likely to occur in males of some species and social stress experiences can greatly affect overall health and disposition (Beery et al, 2020;Larrieu et al, 2017;Zhou et al, 2018). Species such as CD-1 mice will become territorial when enrichment devices are introduced into the environment, disrupting their established hierarchy (McQuaid et al, 2012).…”

Comparative Assessment of Familiarity/Novelty Preferences in Rodents

“…Mice, like rats, can be found in high density groups in areas of human habitation, and these groups are both flexible and gregarious. Mice form dominance hierarchies based on repeated interactions (reviewed in Beery et al, 2020), but did not display selective preferences for familiar same-sex peers, and exhibited low social contact overall.…”