Several experimental studies for assessing the hierarchy of a group in non-human animals test pairs of subjects in isolation. Yet, evidence is growing that the dominance hierarchy differs among individuals when they are tested in groups versus pairs. In the present study, we compare the hierarchy of the same wild-type Norway rats when they are tested in a group versus in the classical dyadic Tube Test. We show that the dominance order derived in groups differed from that inferred in pairs and was less stable in groups. This difference may be due to the presence of bystanders when testing in groups and their absence in isolated pairs. This suggests that the dominance hierarchy in a group is not reliably inferred when testing isolated pairs, and the classic Tube Test should be reconsidered as a standard protocol for dominance assessments in rats.
Puentes-Escamilla, M.A., Schweinfurth, M.K. & Hemelrijk, C.K. (in press). Dominance relations of Norway rats in pairs versus in groups. Animal Behaviour