Display rate and opponent assessment in the Jacky dragon (Amphibolurus muricatus): An experimental analysis

Honest signals allow animals to assess an opponent without the injury risk of fighting. Playback experiments have shown that call rate is an important parameter in the acoustic signals of several taxa. Here we describe an analogous study of a visual display. Male Jacky dragons, Amphibolurus muricatus, respond to intruding conspecifics with a stereotyped series of motor patterns, including a push-up. These displays are typically given in bouts and there is substantial individual variation in inter-bout interval. In a recent video playback experiment, we found that the display rate depicted in two sequences appeared to influence the type of signal response evoked. The present study was designed to systematically examine the importance of this cue, while controlling opponent morphology and all other aspects of signal structure. Male lizards were presented with five digital video stimuli, each depicting the same male conspecific, but with inter-bout intervals that varied over the full natural range. The duration of aggressive push-up responses changed significantly as a function of stimulus properties. Males tracked playback display rate from unusually slow to the population mean, but displayed less to stimuli with unusually fast rates. The interval between display bouts is hence salient to conspecifics, independent of other characteristics. These findings are consistent with the idea that energetically-expensive dynamic visual signals play a role in opponent assessment.