Visually Guided Avoidance in the Chameleon (Chamaeleo chameleon): Response Patterns and Lateralization

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

Relating lateralization of eye use to body motion in the avoidance behavior of the chameleon (Chamaeleo chameleon).

Lateralization is mostly analyzed for single traits, but seldom for two or more traits while performing a given task (e.g. object manipulation). We examined lateralization in eye use and in body motion that co-occur during avoidance behaviour of the common chameleon, Chamaeleo chameleon. A chameleon facing a moving threat smoothly repositions its body on the side of its perch distal to the threat, to minimize its visual exposure. We previously demonstrated that during the response (i) eye use and body motion were, each, lateralized at the tested group level (N = 26), (ii) in body motion, we observed two similar-sized sub-groups, one exhibiting a greater reduction in body exposure to threat approaching from the left and one--to threat approaching from the right (left- and right-biased subgroups), (iii) the left-biased sub-group exhibited weak lateralization of body exposure under binocular threat viewing and none under monocular viewing while the right-biased sub-group exhibited strong lateralization under both monocular and binocular threat viewing. In avoidance, how is eye use related to body motion at the entire group and at the sub-group levels? We demonstrate that (i) in the left-biased sub-group, eye use is not lateralized, (ii) in the right-biased sub-group, eye use is lateralized under binocular, but not monocular viewing of the threat, (iii) the dominance of the right-biased sub-group determines the lateralization of the entire group tested. We conclude that in chameleons, patterns of lateralization of visual function and body motion are inter-related at a subtle level. Presently, the patterns cannot be compared with humans' or related to the unique visual system of chameleons, with highly independent eye movements, complete optic nerve decussation and relatively few inter-hemispheric commissures. We present a model to explain the possible inter-hemispheric differences in dominance in chameleons' visual control of body motion during avoidance

Self-irrigation in the desert rhubarb Rheum palaestinum – a response to Khammash

Khammash (2016) argued that self-irrigation occurs in the desert plant Rheum palaestinum Feinbrun, by collecting dew with its unique 3D leaf morphology and its extremely large leaves rather than collecting rainfall. We agree that collecting dew indeed has a theoretical potential to improve the plant's water economy. However, we suggest that collecting dew can act as an additional mechanism for collecting water rather than an exclusive one. The unknown relative contribution of these two parallel functioning self-irrigation mechanisms to the water economy of the desert rhubarb should be further studied

Self-irrigation in the desert rhubarb Rheum palaestinum – a response to Khammash

Khammash (2016) argued that self-irrigation occurs in the desert plant Rheum palaestinum Feinbrun, by collecting dew with its unique 3D leaf morphology and its extremely large leaves rather than collecting rainfall. We agree that collecting dew indeed has a theoretical potential to improve the plant's water economy. However, we suggest that collecting dew can act as an additional mechanism for collecting water rather than an exclusive one. The unknown relative contribution of these two parallel functioning self-irrigation mechanisms to the water economy of the desert rhubarb should be further studied

Multifocal lenses in coral reef fishes

The optical properties of crystalline lenses were studied in eleven species of coral reef fish from the Red Sea in Eilat, Israel. Three species each of diurnal planktivores, nocturnal planktivores and diurnal herbivores constituted three groups of animals with little within-group variability. In addition we studied two predators, which differed with respect to body size, prey preference, hunting method and diel activity period. All species studied have multifocal lenses. There were statistically significant differences in the optical properties of the lenses between the first three groups and between the predatory species. The properties of the lenses correlate well with known complements of visual pigments and feeding habits. Lenticular zones focusing ultraviolet light were found in two diurnal planktivores. The optical properties of the lens seem to be specifically adapted to the visual needs of each species

Eye durations (proportions) of the Leading Eye or the Following Eye in viewing categories FV or NV.

<p>The durations as a function of threat approach direction. Provided are ANOVA test results.</p