Sensory and environmental influences on display form in Anolis auratus, a grass anole from Panama

SummaryIt is hypothesized that the head movements which make up the introductory portion of the territorial “assertion” display of Anolis auratus function to draw the gaze of conspecifics. Earlier experiments showed that two features of a motion pattern were critical in making it effective at gaining the attention of an anole: (1) it should consist of high acceleration and velocity, and (2) a Fourier transform of the motion pattern should reveal sinusoidal frequency components distinct from those present in motion patterns commonly present in the environment. The most common source of motion in the environment is windblown vegetation. Motion of vegetation typical of the A. auratus habitat was quantified and analyzed by Fourier transform. Assertion displays of a number of individual lizards were filmed and quantified. It was found that the first 3.6 s of the displays consisted of high acceleration/high velocity movements which contained, at certain sinusoidal frequencies, amplitude several times greater than what was present in the vegetation movement. Thus, motion detection properties of the visual system and movement properties of windblown vegetation combine to influence the physical form of this visual display.