Introductory tail-flick of the Jacky dragon visual display: signal efficacy depends upon duration

Abstract

SUMMARY Many animal signals have introductory components that alert receivers. Examples from the acoustic and visual domains show that this effect is often achieved with high intensity, a simple structure and a short duration. Quantitative analyses of the Jacky dragon Amphibolurus muricatusvisual display reveal a different design: the introductory tail-flick has a lower velocity than subsequent components of the signal, but a longer duration. Here, using a series of video playback experiments with a digitally animated tail, we identify the properties responsible for signal efficacy. We began by validating the use of the computer-generated tail, comparing the responses to digital video footage of a lizard tail-flick with those to a precisely matched 3-D animation (Experiment 1). We then examined the effects of variation in stimulus speed, acceleration, duration and period by expanding and compressing the time scale of the sequence (Experiment 2). The results identified several variables that might mediate recognition. Two follow-up studies assessed the importance of tail-flick amplitude (Experiment 3),movement speed and signal duration (Experiment 4). Lizard responses to this array of stimuli reveal that duration is the most important characteristic of the tail-flick, and that intermittent signalling has the same effect as continuous movement. We suggest that signal design may reflect a trade-off between efficacy and cost.

Active space of a movement-based signal: response to the Jacky dragon(Amphibolurus muricatus) display is sensitive to distance, but independent of orientation

“…Our strategy for analyzing movement-based signals combines quantitative analyses of the structure of signals and noise (Peters and Evans, 2003a) with signal-detection experiments (Peters and Evans, 2003b). We use a native Australian agamid lizard, the Jacky dragon (Amphibolurus muricatus), as a model system.…”

“…We began by considering the properties responsible for signal efficacy in the Jacky dragon tail-flick (Peters and Evans, 2003b). We found that duration was more important than speed in evoking an orienting response, with long signals being most successful.…”

“…This is the first experimental analysis of this type for any class of dynamic visual signals. We adapted a strategy analogous to those used in acoustic studies (for a review, see Dooling et al, 2000) and techniques developed in our previous work in the Jacky dragon system (Peters and Evans, 2003b). Signal properties were manipulated using video playback of highly detailed 3D animations.…”

Silent tidbitting in male fowl,Gallus gallus: a referential visual signal with multiple functions

“…3), suggesting that none of them has evolved specifically to have an alerting function (i.e. design for particular efficacy in engaging a visual grasp reflex), as in some other dynamic visual signals (Peters and Evans, 2003). One possible explanation for this may be that the displays contain far more motion in the vertical plane than in the horizontal.…”

Assessment of repeated displays: a test of possible mechanisms

“…Displays can occur in rapid succession, forming a bout. Lizards often modify their displays by adding introductory tail-flicks (Peters and Evans, 2003), or increasing their profile through lateral compression, gular expansion and nuchal crest erection. Previous video playback experiments found that males were sensitive to 'moment-to-moment' variation in the display rate of simulated opponents and the social contingencies governing interactions .…”