Fasting or feasting in a fish social hierarchy

Understanding why and how subordinates of many social animals remain consistently smaller than dominants is important for determining the mechanisms underlying the structure and stability of hierarchical societies. Here we show that competition over food and conflict over social rank are ultimately responsible for the regulation of subordinate growth in the group-living reef fish, Paragobiodon xanthosomus (Gobiidae). Subordinates benefit from reducing their own food intake, and hence growth, when they approach a size where they risk conflict with dominants. Dieting appears to be a behavioural mechanism ensuring that subordinates remain smaller than dominants within the hierarchy.