Behavioral and neuronal underpinnings of safety in numbers in fruit flies

Clara H Ferreira,Marta A Moita

doi:10.1038/s41467-020-17856-4

Abstract

Living in a group allows individuals to decrease their defenses, enabling other beneficial behaviors such as foraging. The detection of a threat through social cues is widely reported, however, the safety cues that guide animals to break away from a defensive behavior and resume alternate activities remain elusive. Here we show that fruit flies display a graded decrease in freezing behavior, triggered by an inescapable threat, with increasing group sizes. Furthermore, flies use the cessation of movement of other flies as a cue of threat and its resumption as a cue of safety. Finally, we find that lobula columnar neurons, LC11, mediate the propensity for freezing flies to resume moving in response to the movement of others. By identifying visual motion cues, and the neurons involved in their processing, as the basis of a social safety cue this study brings new insights into the neuronal basis of safety in numbers.

Highlights

Living in a group allows individuals to decrease their defenses, enabling other beneficial behaviors such as foraging
The decrease in persistent freezing with the increase in group size suggests that there is a signal conveyed by the other flies that increases in intensity with the increase in the number of flies tested together
In this study, we show that flies in groups display a reduction in freezing responses that scales with group size

Summary

Introduction

Living in a group allows individuals to decrease their defenses, enabling other beneficial behaviors such as foraging. It has been suggested that seismic waves produced by fast running in elephants promote vigilance in conspecifics[15] This form of social detection of threat may be advantageous as it does not require the active production of a signal that may render the emitter more conspicuous and vulnerable. Because living in a group allows individuals to decrease their defenses, it enables other globally beneficial behaviors such as foraging. These selective forces on the evolution of social behavior have been demonstrated in a wide range of animals, from invertebrates to mammals[1,2]. The identification of the sensory neurons responsible for social regulation of freezing opens up the possibility to gain mechanistic insight into the safety in numbers effect

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Conclusion