Opponent assessment based on display rate in the Jacky dragon, Amphibolurus muricatus

Many animals signal their resource holding potential (RHP) to deter competitors from engaging them in potentially costly fights. Studies of this opponent assessment function have generated important insights into signal design and evolution. In the case of sounds, rate of production is often a salient feature. We used digital video playback to conduct analogous experiments exploring the importance of temporal variation in visual signals. Our study focused on the push-up display of male Jacky dragons, an Australian agamid lizard. This stereotyped movement-based signal is commonly performed during male-male contests. A previous study has shown that Jacky dragons are sensitive to the overall display rate of a video conspecific. We built upon this finding by investigating the effect of fine-scale changes in display rate. Each playback sequence varied systematically across a different combination of display parameters, while keeping the total number of push-ups constant. Other potential cues, such as morphology and the characteristics of individual motor patterns, were precisely controlled. The aggressive signalling and locomotor behaviour of subject males varied significantly between treatments. Most notably, performance of throat expansions, a typical agamid threat posture, was suppressed by video sequences in which the initial displays were concentrated into bouts. These results show that lizards were sensitive to differences in the temporal structure of display sequences and suggest that this assessment process is extremely rapid; variation during the first few minutes of a simulated interaction was critically important in determining the intensity of aggressive responses.