Abstract
Visual recognition of conspecifics is necessary for a wide range of social behaviours in many animals. Medaka (Japanese rice fish), a commonly used model organism, are known to be attracted by the biological motion of conspecifics. However, biological motion is a composite of both body-shape motion and entire-field motion trajectory (i.e., posture or motion-trajectory elements, respectively), and it has not been revealed which element mediates the attractiveness. Here, we show that either posture or motion-trajectory elements alone can attract medaka. We decomposed biological motion of the medaka into the two elements and synthesized visual stimuli that contain both, either, or none of the two elements. We found that medaka were attracted by visual stimuli that contain at least one of the two elements. In the context of other known static visual information regarding the medaka, the potential multiplicity of information regarding conspecific recognition has further accumulated. Our strategy of decomposing biological motion into these partial elements is applicable to other animals, and further studies using this technique will enhance the basic understanding of visual recognition of conspecifics.
Highlights
Recognition of conspecifics is necessary for a wide range of social behaviours, as it allows effective discrimination among self, kin, predator, prey, competitors, friends, and potential mates[1]; notably, this recognition can be facilitated by various mechanisms, including scent[2,3], auditory recognition[4,5,6], and visual recognition[7]
In addition to appearance information involving conspecifics, it has been suggested that medaka can recognise motion information alone[15], as medaka are attracted by biological motion, represented as point-light stimuli that are produced via motion tracking of real medaka
We decomposed the biological motion of live medaka into posture and motion-trajectory elements and found that each element exhibited significant effects on attraction without significant interaction between the elements; this suggests that medaka can rely separately on information in both of these partial motion elements to identify conspecifics
Summary
Recognition of conspecifics is necessary for a wide range of social behaviours, as it allows effective discrimination among self, kin, predator, prey, competitors, friends, and potential mates[1]; notably, this recognition can be facilitated by various mechanisms, including scent[2,3], auditory recognition[4,5,6], and visual recognition[7]. Multiple taxa of animals can recognise biological motion, including humans[11], primates[13], birds[14], and fish[15,16] This suggests that motion recognition is important for conspecific recognition and that the neurological mechanism is evolutionarily conserved. Three-dimensional (3D) computer graphic animations that imitate real medaka have demonstrated that medaka can be attracted by various elements of appearance information, such as colour and shape, and by elements of motion information, such as global motion trajectory and body-shape-level motion of conspecifics; these aspects have been revealed by subtracting each element from the complete 3D medaka animation[41] These findings suggest that conspecific recognition requires various elements of information, and that medaka can extract information regarding abstract features, even from a portion of the typical elements (i.e., biological motion alone). It has not yet been determined what element(s) of biological motion constitute the minimum components of attractiveness
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