Abstract
The common chameleon, Chamaeleo chameleon, is an arboreal lizard with highly independent, large-amplitude eye movements. In response to a moving threat, a chameleon on a perch responds with distinct avoidance movements that are expressed in its continuous positioning on the side of the perch distal to the threat. We analyzed body-exposure patterns during threat avoidance for evidence of lateralization, that is, asymmetry at the functional/behavioral levels. Chameleons were exposed to a threat approaching horizontally from the left or right, as they held onto a vertical pole that was either wider or narrower than the width of their head, providing, respectively, monocular or binocular viewing of the threat. We found two equal-sized sub-groups, each displaying lateralization of motor responses to a given direction of stimulus approach. Such an anti-symmetrical distribution of lateralization in a population may be indicative of situations in which organisms are regularly exposed to crucial stimuli from all spatial directions. This is because a bimodal distribution of responses to threat in a natural population will reduce the spatial advantage of predators.
Highlights
Changes in body orientation in response to external stimuli are fundamental to animal motion and locomotion and require the perception of one’s location in relation to the relevant stimuli
Body position corrections are often observed in avoidance, such as in the case of locusts (Locusta migratoria)
The angular velocity of 15u/s was the velocity used in the main experiment, as well as in control experiment (a). The results of both control experiments demonstrated that the avoidance response of the chameleons is related to the motion of the visual threat and is not elicited by inertia
Summary
Changes in body orientation in response to external stimuli are fundamental to animal motion and locomotion and require the perception of one’s location in relation to the relevant stimuli. Frequent examples are provided by visually guided responses, including cases in which animals perform highly accurate spatiotemporal corrections of their body or organ position relative to a moving stimulus. Such position corrections, often referred to as ‘‘station keeping’’ [1,2,3,4,5], are observed, for example, in bees maintaining position in front of their hives, or hoverflies closely tracking females in courtship [1,2,3,4,5,6]. When holding onto a twig or branch and exposed to a threat, a locust will respond by actively positioning itself so as to keep on the far side of its perch Such behavior is performed only while the threat is in motion, resulting in minimizing its exposure to that threat [7]. Similar behavior patterns are observed in grasshoppers and cicadas and may well reduce the chances of detection
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