Motion cues tune social influence in shoaling fish

Abstract

Social interactions have important consequences for individual fitness. Collective actions, however, are notoriously context-dependent and identifying how animals rapidly weigh the actions of others despite environmental uncertainty remains a fundamental challenge in biology. By exposing zebrafish (Danio rerio) to virtual fish silhouettes in a maze we isolated how the relative strength of a visual feature guides individual directional decisions and, subsequently, tunes social influence. We varied the relative speed and coherency with which a portion of silhouettes adopted a direction (leader/distractor ratio) and established that solitary zebrafish display a robust optomotor response to follow leader silhouettes that moved much faster than their distractors, regardless of stimulus coherency. Although recruitment time decreased as a power law of zebrafish group size, individual decision times retained a speed-accuracy trade-off, suggesting a benefit to smaller group sizes in collective decision-making. Directional accuracy improved regardless of group size in the presence of the faster moving leader silhouettes, but without these stimuli zebrafish directional decisions followed a democratic majority rule. Our results show that a large difference in movement speeds can guide directional decisions within groups, thereby providing individuals with a rapid and adaptive means of evaluating social information in the face of uncertainty.

The visual social environment affects non-additively neighbor spacing and interaction time in zebrafish

“…Many vertebrates (fish and birds) interact socially in 3D space. Previous findings (Larsch & Baier 2018;Lemasson et al 2018) and ours suggest that the rules underlying these 3D interactions are likely affected by multiple parameters acting simultaneously. In other words, the effects of some visual social parameters may depend on the intensity of other visual social parameters tuning up or down different social behavioral responses.…”

“…The presence of a threat could be quickly transmitted across the group via social information, leading to rapid changes in the spatial configuration of the school ending in spatially tighter (e.g., higher density) schools. More work along the lines of Lemasson et al (2018) should establish the relative relevance of the different sources of visual social information in triggering these spatial structure changes as the number of group members increases (and their position in 3D space changes) in environments with different levels of habitat complexity and visibility.…”

“…The availability of virtual playbacks and robotic animals has allowed for manipulating these social cues to assess their role in tuning 5 social behavior (e.g., Gerlai 2017, Bierbach et al 2018Kim et al 2018). Several studies have manipulated single social cue types at a time (e.g., Butail et al 2015, Bartolini et al 2016; however, we know relatively less about the effects of simultaneous different social cues types on an individual's ability to gather social information and respond to variations in its visual social environment (but see Larsch & Baier 2018;Lemasson et al 2018). This is particularly relevant because understanding how animals respond to variations in the social environment can allow us to identify the rules underlying social interactions (Arganda et al 2012).…”

“…We only considered interactions with a single conspecific as a first attempt to identify some of the simplest rules underlying pairwise social interactions. Future studies should consider how these rules scale up in larger groups (e.g., Lemasson et al 2018).…”

Behavioral traits that define social dominance are the same that reduce social influence in a consensus task

“…In the association task, informed individuals swam quickly and directly towards the 'correct' feeder, inducing following behavior in other group members. Such a rapid change in speed is also known to be an important social cue influencing collective behavior in zebrafish (29). However, this mode of swimming -rapid and straight -was a rare behavior for subordinate males, who typically moved at slow speeds, stayed with the group, and moved without abrupt changes in speed.…”