Data from: Social synchronization of circadian rhythmicity in female mice depends on the number of cohabiting animals

Communal animals often engage in group activities that require temporal synchrony among its members, including synchrony on the circadian timescale. The principles and conditions that foster such collective synchronization are not understood, but existing literature hints that the number of interacting individuals may be a critical factor. We tested this by recording individual circadian body temperature rhythms of female house mice housed singly, in twos (pairs), or in groups of five (quintets) in constant darkness; determining the daily phases of the circadian peak for each animal; and then calculating the cycle-to-cycle phase relationship between cohabiting animals over time. Significant temporal coherence was observed in quintets: the proportion of quintets (4/7), but not pairs (2/8), that became synchronized was greater than could be achieved by the complete simulated reassortment of all individuals. We speculate that the social coupling of individual circadian clocks of group members may be adaptive under certain conditions, and we propose that optimal group sizes in nature may depend not only on species-specific energetics, spatial behaviour and natural history but also on the mathematics of synchronizing assemblies of weakly coupled animal oscillators.

群居动物常开展需要群体成员间实现时间同步的集体活动，其中包括昼夜节律（circadian）时间尺度上的同步性。目前学界尚未阐明促成此类集体同步的原理与条件，但已有研究文献暗示，互动个体的数量可能是关键影响因素。我们将雌性家鼠饲养于持续黑暗环境中，分别设置单笼饲养、成对饲养（2只，pairs）以及5只群居饲养（五鼠组，quintets）三组，以此验证上述假设：记录各组个体的昼夜体温节律（circadian body temperature rhythm），测定每只小鼠的昼夜节律峰值的每日相位，并随时间跨度计算同居个体间逐周期的相位关系。研究在五鼠组中观察到显著的时间一致性：同步化的五鼠组占比为4/7，而成对饲养组的同步占比仅为2/8，该比例高于完全模拟重组所有个体所能达到的同步概率。我们推测，群居成员个体的昼夜节律钟（circadian clock）之间的社交耦合在特定条件下可能具有适应性；并提出，自然界中最优的群体规模不仅取决于物种特异性的能量代谢、空间行为与自然历史特征，还依赖于弱耦合动物振子集合同步化的数学原理。