Cooperative foraging during larval stage affects fitness inDrosophila

Abstract

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