title: Symmetry breaking on density in escaping ants: experiment and alarm pheromone model.
abstract: The symmetry breaking observed in nature is fascinating. This symmetry breaking is observed in both human crowds and ant colonies. In such cases, when escaping from a closed space with two symmetrically located exits, one exit is used more often than the other. Group size and density have been reported as having no significant impact on symmetry breaking, and the alignment rule has been used to model symmetry breaking. Density usually plays important roles in collective behavior. However, density is not well-studied in symmetry breaking, which forms the major basis of this paper. The experiment described in this paper on an ant colony displays an increase then decrease of symmetry breaking versus ant density. This result suggests that a Vicsek-like model with an alignment rule may not be the correct model for escaping ants. Based on biological facts that ants use pheromones to communicate, rather than seeing how other individuals move, we propose a simple yet effective alarm pheromone model. The model results agree well with the experimental outcomes. As a measure, this paper redefines symmetry breaking as the collective asymmetry by deducing the random fluctuations. This research indicates that ants deposit and respond to the alarm pheromone, and the accumulation of this biased information sharing leads to symmetry breaking, which suggests true fundamental rules of collective escape behavior in ants.
authors.affiliation: School of Systems Science, Beijing Normal University, Beijing, China.
authors.forename: Geng
authors.initials: G
authors.lastname: Li
authors.affiliation: School of Systems Science, Beijing Normal University, Beijing, China.
authors.forename: Di
authors.initials: D
authors.lastname: Huan
authors.affiliation: Institute for Theoretical and High Energy Physics, University of Paris 6 (Pierre and Marie Curie), F-75005, Paris, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Roehner
authors.affiliation: The College of Natural Resources and Environment of South China Agricultural University, Guangzhou, China.
authors.forename: Yijuan
authors.initials: Y
authors.lastname: Xu
authors.affiliation: The College of Natural Resources and Environment of South China Agricultural University, Guangzhou, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Zeng
authors.affiliation: School of Systems Science, Beijing Normal University, Beijing, China.
authors.forename: Zengru
authors.initials: Z
authors.lastname: Di
authors.affiliation: School of Systems Science, Beijing Normal University, Beijing, China.
authors.forename: Zhangang
authors.initials: Z
authors.lastname: Han
mesh_terms: D000818:Animals; D001000:Ants / Q000187:drug effects* / Q000502:physiology; D004924:Escape Reaction / Q000187:drug effects*; D008954:Models, Biological; D010675:Pheromones / Q000494:pharmacology*
chemical_list: D010675:Pheromones