The function, development, and evolutionary stability of conventional signals of fighting ability

Abstract Many animals minimize the costs of aggressive conflict by using conventional signals of agonistic ability to assess rivals prior to interacting. Conventional signals are a subset of signals of agonistic ability that appear “arbitrary”, as there is no logical, a priori , link between the signal phenotype and the information the signal conveys. Examples include the black chest patches called “badges of status” in many sparrows and the facial spots in Polistes dominulus wasps. Although there has been consistent interest in conventional signaling over the last 30 years, the area remains surprisingly underexplored. This review addresses previous theoretical and empirical works on agonistic conventional signals and considers three key areas for future research. First, future work that considers a greater diversity of traits will be useful, as many different types of visual, acoustic, and chemical ornaments likely function as conventional agonistic signals. Second, testing the signal value of conventional signals has been a challenge, as responses to conventional signals vary based on factors such as rival-advertised quality, the cost of the contested resource, and the timing or extent of interactions with rivals. As a result, studies assessing the context-dependence of receiver responses will be important, as well as experiments that account for variation in receiver responses across contexts. Finally, the costs that maintain the evolutionary stability of conventional signals have been a persistent source of controversy. Considering multiple costs, especially the interplay between social and physiological costs, may provide new insight into the evolutionary stability of conventional signals.