Abstract
Collective behavior may be elicited or can spontaneously emerge by a combination of interactions with the physical environment and conspecifics moving within that environment. To investigate the relative contributions of these factors in a small millimeter-scale swimming organism, we observed larval zebrafish, interacting at varying densities under circular confinement. If left undisturbed, larval zebrafish swim intermittently in a burst and coast manner and are socially independent at this developmental stage, before shoaling behavioral onset. Our aim was to explore the behavior these larvae as they swim together inside circular confinements. We report here our analysis of a new observation for this well-studied species: in circular confinement and at sufficiently high densities, the larvae collectively circle rapidly alongside the boundary. This is a new physical example of self-organization of mesoscale living active matter driven by boundaries and environment geometry. We believe this is a step forward toward using a prominent biological model system in a new interdisciplinary context to advance knowledge of the physics of social interactions.
Highlights
The emergence of complex collective behavior of natural and artificial motile agents has long been a question of interest to scientists in many disciplines
The transition from disordered to ordered collective motion can be seen across scales, from micron long bacteria and colloids, to millimeter long ants and bees, to centimeter long crickets and bristle-bots, and even to meter-long fish and humans [1,2,3]
Observing larval zebrafish behaving spontaneously at varying densities, from 5 to 130 individuals, in a 5.4 cm diameter arena (Figure 1), we found the animals moved freely within the arena in short bouts of swimming
Summary
The emergence of complex collective behavior of natural and artificial motile agents has long been a question of interest to scientists in many disciplines. For fluid-immersed micro-scale units such as motile bacteria and colloids, it has become clear that mechanical interactions often mediated through the liquid are paramount to the type of eventual patterns [5, 6]. For larger animals such as birds, mechanics are not the only factor as others may become more prominent, e.g., visual input for birds [7], environmental factors for bees [8], sensory stimuli or social cues for humans [9]
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