The Effect of Familiarity Among Social Partners on the Jumping Behavior of Amazon Mollies

ABSTRACT Fish often jump to avoid a risky situation, without having any knowledge about the consequences that can follow. With this work, we set out to understand the decision‐making process behind such behaviors and determine how they are socially modulated. Social species often rely on information from conspecifics to navigate their environment, but for an observer it can be difficult to pin‐point the exact time at which a decision is made by an individual. Here, we utilize the fact that Amazon molly ( Poecilia formosa ), a naturally clonal, livebearing fish, spontaneously performs discrete jumping behavior. In this study, we test the hypothesis that jumping behavior is socially mediated by experimentally creating familiar and non‐familiar pairs and assessing the evasive jumps in a novel environment. Our results suggest that the fish are more likely to jump in order to follow an unfamiliar social partner into unknown surroundings, whereas familiar partners tend to remain in place together. We propose jumping behavior as a biologically relevant and easily quantifiable action, which enables us to address social contagion and decision‐making under uncertainty in animal groups.