Social conformity and propagation of information in collective U-turns of fish schools
Social conformity and propagation of information in collective U-turns of fish schools
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DOI：
10.1098/rspb.2018.0251
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发表时间：
2018-04-25
影响因子：
4.7
通讯作者：
Theraulaz, Guy
中科院分区：
文献类型：
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作者：
Lecheval, Valentin;Jiang, Li;Theraulaz, Guy
移动的动物群体，如鱼群或鸟群，经常由于个体方向的随机波动而突然集体改变其行进方向。然而，这些行为波动在个人层面产生并在群体中传播的机制仍不清楚。在这项研究中，我们将实验和理论相结合的方法研究了在环形水箱中游泳的拉米鼻河豚（Hemigrammus rhodostomus）群体中的自发集体u型转弯。u型转弯意味着鱼在顺时针和逆时针方向之间切换它们的方向。我们重建了个体单独和不同大小的群体移动的轨迹。我们展示了群体在集体掉头前降低了游泳速度。这与先前的理论预测一致，即速度的降低促进了群体中航向波动的放大，这可能引发u型转弯。这些集体的180度大转弯大多是由站在群体前面的个人发起的。一旦一个人开始掉头，新的方向就会在整个群体中从前到后传播，没有放大或抑制，就像多米诺骨牌倒下的动力一样。集体掉头之间的平均时间随着群体规模的增加而急剧增加。我们开发了一个Ising自旋模型，将鱼类之间的各向异性和不对称相互作用及其非线性跟随大多数邻居（社会从众）的趋势整合在一起。该模型定量再现了实验中观察到的动力学和集体u型转弯频率的关键特征。
Moving animal groups such as schools of fishes or flocks of birds often undergo sudden collective changes of their travelling direction as a consequence of stochastic fluctuations in heading of the individuals. However, the mechanisms by which these behavioural fluctuations arise at the individual level and propagate within a group are still unclear. In this study, we combine an experimental and theoretical approach to investigate spontaneous collective U-turns in groups of rummy-nose tetra (Hemigrammus rhodostomus) swimming in a ring-shaped tank. U-turns imply that fish switch their heading between the clockwise and anticlockwise direction. We reconstruct trajectories of individuals moving alone and in groups of different sizes. We show that the group decreases its swimming speed before a collective U-turn. This is in agreement with previous theoretical predictions showing that speed decrease facilitates an amplification of fluctuations in heading in the group, which can trigger U-turns. These collective U-turns are mostly initiated by individuals at the front of the group. Once an individual has initiated a U-turn, the new direction propagates through the group from front to back without amplification or dampening, resembling the dynamics of falling dominoes. The mean time between collective U-turns sharply increases as the size of the group increases. We develop an Ising spin model integrating anisotropic and asymmetrical interactions between fish and their tendency to follow the majority of their neighbours nonlinearly (social conformity). The model quantitatively reproduces key features of the dynamics and the frequency of collective U-turns observed in experiments.