Abstract
Animals, from invertebrates to humans, stabilize the panoramic optic flow through compensatory movements of the eyes, the head or the whole body, a behavior known as optomotor response (OR). The same optic flow moved clockwise or anticlockwise elicits equivalent compensatory right or left turning movements, respectively. However, if stimulated monocularly, many animals show a unique effective direction of motion, i.e., a unidirectional OR. This phenomenon has been reported in various species from mammals to birds, reptiles, and amphibious, but among invertebrates, it has only been tested in flies, where the directional sensitivity is opposite to that found in vertebrates. Although OR has been extensively investigated in crabs, directional sensitivity has never been analyzed. Here, we present results of behavioral experiments aimed at exploring the directional sensitivity of the OR in two crab species belonging to different families: the varunid mud crab Neohelice granulata and the ocypode fiddler crab Uca uruguayensis. By using different conditions of visual perception (binocular, left or right monocular) and direction of flow field motion (clockwise, anticlockwise), we found in both species that in monocular conditions, OR is effectively displayed only with progressive (front-to-back) motion stimulation. Binocularly elicited responses were directional insensitive and significantly weaker than monocular responses. These results are coincident with those described in flies and suggest a commonality in the circuit underlying this behavior among arthropods. Additionally, we found the existence of a remarkable eye dominance for the OR, which is associated to the size of the larger claw. This is more evident in the fiddler crab where the difference between the two claws is huge.
Highlights
When an animal, regardless of being a fly, a mouse, a lizard or a human, rotates its vision tends to blur
We measured the optomotor response (OR) of 19 Neohelice evoked by clockwise (CW) or anticlockwise (ACW) rotations of the visual panorama in animals seeing with the two eyes, with the left eye reversibly occluded and with the right eye reversibly occluded
When assessed in monocular conditions, fiddler crabs displayed directional OR preferences similar to those of Neohelice: crabs seeing the stimulus with the left eye responded mostly to anticlockwise motion (p = 0.006), while crabs seeing it with the right eye tended to respond mainly when the panorama moved clockwise (p = 0.055; Figure 2B)
Summary
Regardless of being a fly, a mouse, a lizard or a human, rotates (or in the laboratory is exposed to the rotation of the visual panorama) its vision tends to blur. Animals stimulated with a pattern of high-contrast vertical strips moving clockwise (CW) or anticlockwise (ACW) perform OR in the corresponding direction with similar strength, but only if they are seeing the stimulus with the two eyes When this experiment is repeated occluding one eye, i.e., in a monocular condition, many animals show a marked directional preference. This happens when presenting the stimulus over one lateral visual field in a position that can only be seen by one eye in animals, like flies, fishes, etc., that possess a small field of binocular superposition This phenomenon is referred to as unidirectional optomotor response and has been reported in various species from mammals to birds, reptiles, amphibious, fishes, and flies (Mowrer, 1936; Fukuda, 1959; Tauber and Atkin, 1968; Collewijn, 1969; Easter, 1972; Jardon and Bonaventure, 1995; Duistermars et al, 2012). To our knowledge, no systematic studies have been performed to investigate whether there is a preferred direction of OR in monocularly seeing crabs
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
