title: The effect of changing topography on the coordinated marching of locust nymphs.
abstract: Collective motion has traditionally been studied in the lab in homogeneous, obstacle-free environments, with little work having been conducted with changing landscapes or topography. Here, the impact of spatial heterogeneity on the collective motion exhibited by marching desert locust nymphs was studied under controlled lab conditions. Our experimental circular arenas, incorporating a funnel-like narrowing followed by re-widening, did not constitute a major barrier to the locusts but, rather, mimicked a changing topography in the natural environment. We examined its effects on macroscopic features of the locust collective behavior, as well as the any changes in their marching kinematics. A major finding was that of the limited extent to which the changing topography affected system-level features of the marching locust group, such as the order parameter and the fraction of walking individuals, despite increased crowding at the funnel. Overall, marching kinematics was also very little affected, suggesting that locust marching bands adjust to the environment, with little effect on the overall dynamics of the group. These findings are in contrast to recent theoretical results predicting that environmental heterogeneities qualitatively alter the dynamics of collectively moving particles; and highlight the crucial role of rapid individual plasticity and adaptability in the dynamics of flocks and swarms. Our study has revealed other important features of the marching behavior of the desert locust in addition to its robustness: the locusts demonstrated both, clear thigmotaxis and a tendency to spread-out and fill the available space.
authors.affiliation: Department of Zoology, Tel Aviv University, Tel Aviv, Israel; Current affiliation:  The Department of Collective Behaviour at the University of Konstanz/Max Planck Institute of Ornithology, Konstanz, Germany.
authors.forename: Guy
authors.initials: G
authors.lastname: Amichay
authors.affiliation: Department of Mathematics, Bar-Ilan University , Ramat Gan , Israel.
authors.forename: Gil
authors.initials: G
authors.lastname: Ariel
authors.affiliation: Department of Zoology, Tel Aviv University, Tel Aviv, Israel; Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Amir
authors.initials: A
authors.lastname: Ayali
keywords: Collective motion; Environmental effects; Locust marching bands; Schistocerca gregaria; Spatial heterogeneity; Swarming; Topological changes