Air-breathing synchrony in juvenile Arapaima gigas reveals collective coordination under individual physiological constraints.

Animal collectives can exhibit striking synchrony in behavior even when members differ consistently among each other when alone. While synchrony in collective movements or signaling as found in schooling fish or flashing fireflies is well-studied, these behaviors typically do not require individuals to compromise physiological needs when adjusting direction, speed, or timing, as they are generally almost cost-free to produce. In contrast, less is known about how individuals coordinate state-dependent behaviors shaped by internal physiological needs that may limit their ability to conform. We address this question by combining agent-based modeling with empirical observations of a distinctive case of synchronization in fish - the collective air-breathing of juvenile Arapaima gigas. We show that individuals differ consistently in surfacing rhythms when alone, yet in a large shoal of about 200 same-aged individuals, a substantial portion of the group surfaces within the same second. Our analysis, supported by individual-based simulations of inherently non-periodic coupled oscillators (units that act stochastically in isolation), reveals a simple social interaction rule by which synchrony emerges despite individual variation in surfacing rhythms. The model, matched to our empirical data, suggests that assortative social responsiveness ("cluster synchrony") can buffer internal constraints, enabling coordination without overriding individual physiological limitations.