Abstract
The nest architecture of social insects deeply impacts the spatial distribution of nestmates their interactions, information exchanges and collective responses. In particular, the number of nest entrances can influence the interactions taking place beyond the nest boundaries and the emergence of collective structures like foraging trails. Here, we investigated in the field how the number of nest entrances impacted the foraging dynamics of Myrmica rubra ant colonies. We located the nest entrances where recruitment occurred towards sugar feeders placed in their surroundings. The nests showed one or multiple entrance(s) aggregated in clusters spaced by at least 15 cm. Foragers from colonies with two clusters of entrances were distributed more homogeneously among the feeders than those of colonies with one cluster. In addition, foragers always returned to the first discovered feeder and demonstrated a high fidelity to their original entrance. Finally, a multi-agent model highlighted that additional entrances and clusters of entrances delayed the mobilisation of workers but favoured the simultaneous exploitation of several sources, which was further enhanced by the spatial fidelity of foragers. Multiple nest entrances seem to be a way for medium-sized colonies to benefit from advantages conferred by polydomy while avoiding associated costs to maintain social cohesion.
Highlights
Social foraging has been described in many species including fish, birds, mammals and insects
Collective foraging has been extensively studied in social insects as it raises challenging questions about the mechanisms underlying the coordination of hundreds of individuals in the absence of any task managers, or centralized decision-making [9,10]
In most ant species and in honeybees, collective foraging is based on the sharing of information through recruitment of naive individuals by informed ones [11,12] and on the transfer of food from foragers to workers, larvae, or queens that stay inside the nest. [13,14]
Summary
Social foraging has been described in many species including fish, birds, mammals and insects (reviewed in [1]). Collective foraging in social insects usually relies on self-organized processes in which individual behaviours are regulated through positive and negative feedbacks that amplify or dampen the emergent group behaviours [15]. The emergence of these collective behaviours requires a critical number of interactions among individuals to take place [10,16]. Reaching a threshold of interacting individuals implies that numerous trade-offs have to be solved or optimized by the colony These include (i) how to divide the workforce between scouts searching for food and recruits waiting in the nest for Insects 2020, 11, 317; doi:10.3390/insects11050317 www.mdpi.com/journal/insects
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