Abstract

How animals use sensory information to weigh the risks vs. benefits of behavioral decisions remains poorly understood. Inter-male aggression is triggered when animals perceive both the presence of an appetitive resource, such as food or females, and of competing conspecific males. How such signals are detected and integrated to control the decision to fight is not clear. For instance, it is unclear whether food increases aggression directly, or as a secondary consequence of increased social interactions caused by attraction to food. Here we use the vinegar fly, Drosophila melanogaster, to investigate the manner by which food influences aggression. We show that food promotes aggression in flies, and that it does so independently of any effect on frequency of contact between males, increase in locomotor activity or general enhancement of social interactions. Importantly, the level of aggression depends on the absolute amount of food, rather than on its surface area or concentration. When food resources exceed a certain level, aggression is diminished, suggestive of reduced competition. Finally, we show that detection of sugar via Gr5a+ gustatory receptor neurons (GRNs) is necessary for food-promoted aggression. These data demonstrate that food exerts a specific effect to promote aggression in male flies, and that this effect is mediated, at least in part, by sweet-sensing GRNs.

Highlights

  • Metazoan organisms in nature constantly face behavioral choices

  • Fly aggression assays are typically performed in the presence of a small central food patch [26,50] or an elevated cup containing food [3,22,27,51,52], placed in a larger chamber (Figure 1c, left and Figure S4a)

  • As aggressive interactions between males depend on non-volatile cuticular hydrocarbon pheromones that are detected by contact chemoreceptors [1,3,4,10,12,14,18,22,27,55,56,57], an increase in encounters might enhance aggression indirectly, by promoting pheromone detection

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Summary

Introduction

Metazoan organisms in nature constantly face behavioral choices. Depending on the actions selected, an animal may gain access to potential resources or risk starvation, predation or agonistic interactions. Aggression is an ideal system in which to study how the nervous system makes value-based decisions, as the decision to fight comes with apparent costs and benefits, and requires the assessment of a potential conflict: the detection of attractive resources and competitors who limit access to such resources. As in many other species, Drosophila males exhibit a genderspecific repertoire of stereotyped aggressive behaviors [1,2,3,4,5,6,7,8,9]. The detection of cues from conspecific males is a necessary but not sufficient condition for aggression: male flies will not fight unless a resource, such as food or females, is present [1,3,4,9,22,23,24,26,27,28,29,30,31,32]

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