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Stigmergic construction and topochemical information shape ant nest architecture
Edited by William Bialek, Princeton University, Princeton, NJ, and approved December 4, 2015 (received for review May 19, 2015)

Significance
Social insects build some of the most complex nests found in the animal kingdom. Here, we use experiments and modeling to decipher the mechanisms involved in the coordination of nest building in the ant Lasius niger: we first characterize nest architecture and its growth with 3D imaging techniques; then, we test the building responses of individual ants to artificial stimuli. A model entirely based on experimental data confirms that the individual level interactions and building rules are sufficient to reproduce the nest growth dynamics and the spatial patterns observed for real ant nests. Our results show that a pheromone added by ants to the building material is a key factor that controls the growth and form of nest architecture.
Abstract
The nests of social insects are not only impressive because of their sheer complexity but also because they are built from individuals whose work is not centrally coordinated. A key question is how groups of insects coordinate their building actions. Here, we use a combination of experimental and modeling approaches to investigate nest construction in the ant Lasius niger. We quantify the construction dynamics and the 3D structures built by ants. Then, we characterize individual behaviors and the interactions of ants with the structures they build. We show that two main interactions are involved in the coordination of building actions: (i) a stigmergic-based interaction that controls the amplification of depositions at some locations and is attributable to a pheromone added by ants to the building material; and (ii) a template-based interaction in which ants use their body size as a cue to control the height at which they start to build a roof from existing pillars. We then develop a 3D stochastic model based on these individual behaviors to analyze the effect of pheromone presence and strength on construction dynamics. We show that the model can quantitatively reproduce key features of construction dynamics, including a large-scale pattern of regularly spaced pillars, the formation and merging of caps over the pillars, and the remodeling of built structures. Finally, our model suggests that the lifetime of the pheromone is a highly influential parameter that controls the growth and form of nest architecture.
Footnotes
↵1Present address: Unit of Social Ecology, Université Libre de Bruxelles, 1050 Bruxelles, Belgium.
- ↵2To whom correspondence should be addressed. Email: guy.theraulaz{at}univ-tlse3.fr.
Author contributions: G.T. designed research; A.K. and J.G. developed the 3D model; A.K., A.P., C.S., C.J., and G.T. performed research; M.C. and P.K. contributed new reagents/analytic tools; A.K., J.G., A.P., C.S., M.C., P.K., C.J., and G.T. analyzed data; and J.G., C.J., and G.T. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1509829113/-/DCSupplemental.
Freely available online through the PNAS open access option.
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