Abstract
Considerable progress has been made over the past few decades on how animals use social information. In the case of species relying on visual social information to make decisions, studies have often assessed the effects of different manipulated sources of information one at a time. In this study, we assessed whether zebrafish modified its spacing behavior and interaction time in an additive or multiplicative way relative to multiple sources of visual social information using video playbacks. We manipulated simultaneously: (a) the magnitude of the social cues (by varying the size of the virtual fish), (b) the level of social risk (low, high based on the position of the virtual fish in the water column), and (c) the perceived depth of the social cues (visual horizon absent or present). Each of these factors independently affected spacing behavior (zebrafish increased the separation distance with larger virtual fish, with lower visual social risk, and when depth perception was enhanced), but they did not affect interaction time. However, some of these factors interacted significantly, such that their effects on social behavior depended on each other. For instance, zebrafish decreased their separation distance under high vs. low risk conditions when the virtual fish was the same or smaller size, but this risk effect disappeared with larger virtual fish likely to avoid aggression. Also, zebrafish decreased their separation distance when perceived depth was enhanced under low risk, but the perceived depth effect became less pronounced under high risk probably due to dilution effects. Overall, the effects of certain visual social parameters depend on the intensity of other visual social parameters, ultimately tuning up or down different social behavioral responses in a 3D environment. We discuss the implications for the spatial organization of fish schools.
