Spatial and social structure of rewilded laboratory mice

Abstract

AbstractAs an essential biomedical model organism, house mice have been studied intensely under laboratory conditions, yet they evolved to survive and reproduce in complex and dynamic natural environments. There has been recent interest in the study of ‘rewilded’ mice in outdoor environments, particularly for understanding the brain and behavior, yet little work has examined lab mouse behavior under free-living conditions. Here, we develop and implement a repeatable field assay to characterize the emergent spatial and social structure of mice. We examine populations of male and female of C57BL/6J (C57) mice over 10 days in large outdoor field enclosures and compare them to populations of recently wild-derived outbred house mice under the same conditions. We observed shared aspects of space use and social structure across all trials but found that C57 societies differed from those emerging from outbred mice across multiple dimensions. Males of both genotypes established and then defended territories, though multiple territorial behaviors are muted in C57 compared to outbred mice. Female C57 mice spent more time associating with other individuals, showed less bias towards interacting with their prior cage mates, and explored more space relative to all other groups. These behavioral differences resulted in C57 mice repeatedly forming more densely connected social networks than outbred wild-derived mice. This work establishes a high-throughput method for examining complex societies of lab mice under semi-natural conditions. Importantly this work demonstrates that C57 mice recapitulate many, but not all, aspects of social structures generated by wild-derived mice in outdoor conditions. Rewilding allows for tractable, replicable, and ecologically realistic approaches to studying mouse behavior and can facilitate the study of the biological basis of higher order social organization.HighlightsWe describe emergent spatial and social structures of rewilded C57BL/6J (C57) lab mice across replicated 10-day trials in outdoor field enclosures and compare them to wild-derived outbred mice in the same assay.Both C57 and outbred males rapidly establish and maintain territories, though the expression of many territorial behaviors are muted in C57 relative to outbred males.C57 females explore the field enclosures substantially more than any other group and do not show a bias toward associating with previous cage mates, whereas outbred females show a strong bias in favor of associating with previous cage mates.With the exception of C57 females, most mice spent the majority of their recorded time alone.We detect significant differences in social structure between the genotypes, highlighting the repeatability of social structure given the same initial starting conditions. The resulting societies formed by C57 mice are less modular and more densely connected than those formed by wild-derived outbred mice.