WATT*, M.J.; FORSTER, G.L.; JOSS, J.M.P.; University of South Dakota; University of South Dakota; Macquarie University, Australia: Perception of Honest Signals mediates Aggressive Responses of Male Jacky Dragons

Male Jacky Dragons (Amphibolurus muricatus) utilize stereotyped motor displays to convey aggression and territoriality. Individual variation exists within one component of this display, such that the frequency and duration of forelimb pushups co-vary with body size (g/cm), suggesting that pushup characteristics convey information about individual body size that could mediate the course of aggressive interactions. This hypothesis was tested directly using video playback. Pushup frequency and duration were manipulated within video footage of an average-sized aggressively displaying lizard to produce three video stimuli, representing males of smaller than average body size, average body size, and larger than average body size. All other behavioral variables and importantly, actual body size itself, were held constant across stimuli. The three video stimuli were presented at life-size to territory-holding male subjects of varying body size in a random order. Subjects responded most aggressively to the stimulus in which manipulated pushup characteristics conveyed an apparent body size most closely matching their own, and decreased aggression towards stimuli where a larger or smaller body size than the subject was conveyed. These results fit the sequential assessment model of aggressive communicative exchange, which suggests that the production rates of signals revealing body size or fighting ability increase during encounters where opponents are most closely matched in these attributes. Moreover, results support the hypothesis that the duration and number of pushups within A. muricatus displays are honest signals of body size, which may allow opponents to assess each other effectively without constant recourse to physical combat.