Social bonds and cooperative assortment in a fast-living species: insights from laboratory rats

Background: Differentiated and stable affiliative relationships (social bonds) are typically expected in slow-living species, where long lifespans allow delayed social benefits to be realised. Fast-living species, in contrast, are predicted to rely on immediate payoffs and show fewer enduring partnerships. Evolutionary theory further predicts that assortative associations among cooperative individuals can stabilise cooperation within groups. Laboratory rats (Rattus norvegicus), despite being fast-living, exhibit complex social behaviours, providing an ideal system to test these predictions.

Materials and Methods: We conducted six months of continuous observations of six stable groups of 16 rats, recording affiliative interactions to construct social networks. Individual cooperative tendencies were assessed using an experimental allogrooming paradigm, allowing us to evaluate whether cooperative individuals preferentially associate.

Results: Preliminary analyses indicate that rats form selective and stable social bonds, with patterns of repeated affiliative interactions persisting over time. Analyses of assortative mixing by cooperative tendencies are ongoing.

Conclusions: Our findings provide initial evidence that stable social bonds can emerge in fast-living species. Continued analyses will clarify whether cooperative assortment further contributes to social structure, offering insight into the conditions under which social complexity arises.