期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：51
页码：14615-14620
DOI：10.1073/pnas.1611509113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceWhen ants that cooperatively carry large food items encounter obstacles, they switch their collective motion from radial, nest-bound movement to nearly deterministic, tangential oscillations that facilitate obstacle circumvention. This oscillatory motion cannot be explained by a "wisdom-of-the-crowds" model in which all ants are informed of the direction to the nest and the collective motion reflects an average effort. Rather, oscillations emerge due to two, often conflicting, forces: Some ants pull the load toward the nest whereas others align their pull with the momentary direction of motion. Interestingly, these two forces suffice to generate both nest-bound and oscillatory motion without any requirement that individual ants directly sense the obstacle. This is an example of emergent problem solving at the group-level scale. Collective motion by animal groups is affected by internal interactions, external constraints, and the influx of information. A quantitative understanding of how these different factors give rise to different modes of collective motion is, at present, lacking. Here, we study how ants that cooperatively transport a large food item react to an obstacle blocking their path. Combining experiments with a statistical physics model of mechanically coupled active agents, we show that the constraint induces a deterministic collective oscillatory mode that facilitates obstacle circumvention. We provide direct experimental evidence, backed by theory, that this motion is an emergent group effect that does not require any behavioral changes at the individual level. We trace these relaxation oscillations to the interplay between two forces; informed ants pull the load toward the nest whereas uninformed ants contribute to the motions persistence along the tangential direction. The models predictions that oscillations appear above a critical system size, that the group can spontaneously transition into its ordered phase, and that the system can exhibit complete rotations are all verified experimentally. We expect that similar oscillatory modes emerge in collective motion scenarios where the structure of the environment imposes conflicts between individually held information and the groups tendency for cohesiveness.
关键词：collective motion ; animal groups ; emergent behavior ; statistical physics ; social insects
