Aggressive signal design in the Jacky dragon (Amphibolurus muricatus): display duration affects efficiency

Design characteristics of signals, such as their duration, may have evolved to maximize signal efficiency. It is commonly assumed that constraints on signal design have usually shaped the most optimal display characteristics to improve signal transmission and information transfer of the signaller, and detection by intended receivers. In this study, we tested whether the characteristics (duration, speed and frequency) of an aggressive display, the push-up body rock, exhibited by the Jacky dragon (Amphibolurus muricatus) have likely evolved for optimal signal efficiency, as it is able to draw attention to the signaller. We performed two video playback experiments using high-resolution 3D animations testing the effect of variation in push-up body rock structure. In experiment 1, we manipulated push-up body rock display structure. We gradually increased the number of push-ups exhibited by a digitally animated Jacky dragon increasing the overall display duration. In experiment 2, we developed four stimuli based on population-typical push-up body rock display for duration (short and long), and frequency of push-ups (1 or 5 consecutive push-ups) by manipulating push-ups' speed. In both experiments, we measured the probability of an orienting response and response latency of focal lizards when being exposed to the different stimuli. Our results showed that display duration is critically important for signal efficiency in the aggressive push-up body rock display. If we are to understand the design characteristics of signals used in animal communication, then it appears important to consider the possible trade-off between signal efficiency and costs.