Avoidance of a moving threat in the common chameleon (Chamaeleo chamaeleon): rapid tracking by body motion and eye use
A chameleon (Chamaeleo chamaeleon) on a perch responds to a nearby threat by moving to the side of the perch opposite the threat, while bilaterally compressing its abdomen, thus minimizing its exposure to the threat. If the threat moves, the chameleon pivots around the perch to maintain its hidden position. How precise is the body rotation and what are the patterns of eye movement during avoidance? Just-hatched chameleons, placed on a vertical perch, on the side roughly opposite to a visual threat, adjusted their position to precisely opposite the threat. If the threat were moved on a horizontal arc at angular velocities of up to 85°/s, the chameleons co-rotated smoothly so that (1) the angle of the sagittal plane of the head relative to the threat and (2) the direction of monocular gaze, were positively and significantly correlated with threat angular position. Eye movements were role-dependent: the eye toward which the threat moved maintained a stable gaze on it, while the contralateral eye scanned the surroundings. This is the first description, to our knowledge, of such a response in a non-flying terrestrial vertebrate, and it is discussed in terms of possible underlying control systems.
KeywordsVisually guided tracking Threat avoidance Eye movement Chameleon Role-dependent eye movement
The research was supported by the Israel Science Foundation (ISF). We thank Ido Izhaki for statistical advice and Nina Dinov and Nir Keshales for support throughout the research. The thorough comments of the two anonymous referees were of extreme help.
Monocular gaze under three different threat angular velocities. An overhead view of four individuals performing an avoidance response under low (counterclockwise [CCW] and clockwise [CW]), medium (CCW) and high (CW) threat angular velocities. (WMV 13861 kb)
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