Abstract

Cooperative behavior can confer advantages to animals. This is especially true for cooperative foraging which provides fitness benefits through more efficient acquisition and consumption of food. While examples of group foraging have been widely described, the principles governing formation of such aggregations and rules that determine group membership remain poorly understood. Here, we take advantage of an experimental model system featuring cooperative foraging behavior in Drosophila. Under crowded conditions, fly larvae form coordinated digging groups (clusters), where individuals are linked together by sensory cues and group membership requires prior experience. However, fitness benefits of Drosophila larval clustering remain unknown. We demonstrate that animals raised in crowded conditions on food partially processed by other larvae experience a developmental delay presumably due to the decreased nutritional value of the substrate. Intriguingly, same conditions promote the formation of cooperative foraging clusters which further extends larval stage compared to non-clustering animals. Remarkably, this developmental retardation also results in a relative increase in wing size, serving an indicator of adult fitness. Thus, we find that the clustering-induced developmental delay is accompanied by fitness benefits. Therefore, cooperative foraging, while delaying development, may have evolved to give Drosophila larvae benefits when presented with competition for limited food resources.

Highlights

  • Group foraging is a major component of cooperative animal behavior (Allee 1927)

  • Our study tests the idea that cooperative foraging among fruit fly larvae has a fitness benefit that is measured as body size and developmental time

  • We find mixed results in that the duration of larval stage is increased but despite crowding, eclosed adults have normal size when raised in processed food, as opposed to their solitary digging counterparts that display lower fitness in similar conditions

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Summary

Introduction

Group foraging is a major component of cooperative animal behavior (Allee 1927). It can be defined as inter- and intraspecific cooperation in search, acquisition, defense and consumption of common food resources, and can provide benefits in survival and reproduction for a variety of animals (Sumpter 2005; Giraldeau and Caraco 2018). Aggregation can lead to a decreased risk of predation (Turchin and Kareiva 1989; Rohlfs and Hoffmeister 2004) All of these factors increase an individual’s chances of survival and reproductive success which serve as the main measures of fitness (Clark and Mangel 1986). Benefits of cooperative foraging often take effect under certain conditions when availability and distribution of food resources determine the advantage of cooperation (Monaghan and Metcalfe 1985; Scheel and Packer 1991; Eklöv 1992; Amor et al 2010) This may serve an example of Allee effect (Courchamp et al 1999) in context of cooperative feeding, where an individual’s fitness gains correlate with group size and density only to a certain limit, beyond which acquired benefits get leveled and are negatively outweighed by emerging complex non-trophic factors of group membership, such

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