Mosquitofish use the past experiences of others with risk to make shoaling decisions

In social species, individuals can use a variety of cues to inform their association patterns. For example, individuals might use information about the rank, recent diet and disease state of potential partners to make association decisions. However, whether individuals use the past experiences of others with predation risk to inform their association decisions remains unknown. Associating with experienced individuals might enable social transmission of predator information and prepare individuals for dangers they have not yet encountered personally. Alternatively, individuals might avoid such predator-experienced individuals and the potential high predation risk nearby. Here, I manipulated the exposure to predation risk of laboratory-born mosquitofish, Gambusia affinis, creating high-risk individuals (exposed to alarm cues 9 x over 18 days) and low-risk individuals (exposed to water only). I tested preference of naive laboratory-born focal fish to associate with these high-risk and low-risk individuals, allowing both visual and chemical cues, in a choice test. Under safe conditions, focal fish associated equally with the high-risk and low-risk individuals. I then added alarm cue to the testing tank and again measured association preferences. Under these risky conditions, the focal fish increased their time spent associating with the low-risk partner. Importantly, high-risk and low-risk partners did not differ in swimming activity. These results suggest that during interactions, individuals can not only detect the past experiences of others with predation risk, but that they use this information to alter their shoaling decisions under certain conditions, specifically when they themselves encounter cues of predation risk. (C) 2019 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.