The integration of function and ontogeny in the evolution of status signals

We review functional and developmental hypotheses regarding signals of status, traits that provide only information about an individual's ability to win in contests over a resource. The evidence that status signals are true badges (i.e., conventional signals with no production or maintenance costs) is relatively weak, and is based more on the lack of evidence for handicap signaling. We nevertheless review possible use costs that might preserve honesty in a true badge system. One type of a dominant-imposed cost has been well-tested, but we discuss other possibilities and some potential costs imposed by non-dominants. In general, we find that while recent theory has established a clear basis for stable signaling involving true badges, empirical work is mixed and in no system is there convincing evidence that costs and benefits combine to establish a stable signaling system. Costs are also integral to development. The ontogeny of conventional signals by definition cannot involve any costs, yet ability should somehow be incorporated into signal development. We review two possible mechanisms that could accomplish this, the dual-effect of hormones and social feedback. The evidence supporting the first is suggestive but weak and needs refining. No study has explicitly tested for social feedback, yet this seems the most likely mechanism to appropriately link the use costs maintaining reliability with signal development. Status-signals continue to provide opportunities for novel research, and they provide good test cases for broader ideas about the ecology and evolution of communication.