Department of Biological Sciences, Dartmouth College, 78 College Street, Hanover, NH, 03755, USA.
Graduate Program in Ecology, Evolution, Environment, and Society, Dartmouth College, Hanover, NH, 03755, USA.
Sci Rep. 2022 May 7;12(1):7508. doi: 10.1038/s41598-022-11469-1.
Collective movement may emerge if coordinating one's movement with others produces a greater benefit to oneself than can be achieved alone. Experimentally, the capacity to manoeuvre simulated groups in the wild could enable powerful tests of the impact of collective movement on individual decisions. Yet such experiments are currently lacking due to the inherent difficulty of controlling whole collectives. Here we used a novel technique of experimentally simulating the movement of collectives of social hermit crabs (Coenobita compressus) in the wild. Using large architectural arrays of shells dragged across the beach, we generated synchronous collective movement and systematically varied the simulated collective's travel direction as well as the context (i.e., danger level). With drone video from above, we then tested whether focal individuals were biased in their movement by the collective. We found that, despite considerable engagement with the collective, individuals' direction was not significantly biased. Instead, individuals expressed substantial variability across all stimulus directions and contexts. Notably, individuals typically achieved shorter displacements in the presence of the collective versus in the presence of the control stimulus, suggesting an impact of traffic. The absence of a directional bias in individual movement due to the collective suggests that social hermit crabs are individualists, which move with a high level of opportunistic independence, likely thanks to the personal architecture and armour they carry in the form of a protective shell. Future studies can manipulate this level of armour to test its role in autonomy of movement, including the consequences of shell architecture for social decisions. Our novel experimental approach can be used to ask many further questions about how and why collective and individual movement interact.
如果与他人协调行动能给自己带来比独自行动更大的好处，那么集体行动就有可能出现。在实验中，模拟野外群体运动的能力可以有力地检验集体行动对个体决策的影响。然而，由于完全控制整个群体的固有困难，目前还缺乏这样的实验。在这里，我们使用了一种新颖的技术，在野外实验模拟群居寄居蟹（Coenobita compressus）的集体运动。我们利用大型建筑贝壳阵列在海滩上拖动，产生同步的集体运动，并系统地改变模拟群体的行进方向和环境（即危险水平）。然后，我们用无人机从上方拍摄视频，测试焦点个体是否会受到集体运动的影响。我们发现，尽管个体与集体有密切的互动，但它们的运动方向并没有明显的偏向。相反，个体在所有刺激方向和环境下都表现出了相当大的可变性。值得注意的是，与控制刺激相比，个体通常在集体存在的情况下移动距离较短，这表明存在交通影响。由于集体的存在，个体运动没有明显的方向偏向，这表明群居寄居蟹是个体主义者，它们以高度机会主义的独立性运动，这可能要归功于它们携带的个人建筑和盔甲，即保护壳。未来的研究可以操纵这种盔甲水平来检验其对运动自主性的作用，包括外壳结构对社会决策的影响。我们新颖的实验方法可以用来进一步探讨集体和个体运动是如何相互作用的，以及为什么会相互作用。
