Data from: Density-dependent movement and the consequences of the Allee effect in the model organism Tetrahymena

1. Movement and dispersal are critical processes for almost all organisms in natural populations. Understanding their causes and consequences is therefore of high interest. While both theoretical and empirical work suggests that dispersal, more exactly emigration, is plastic and may be a function of local population density, the functional relationship between the underlying movement strategies and population density has received less attention. 2. We here present evidence for the shape of this reaction norm and are able to differentiate between three possible cues: the relative number of individuals, the presence of metabolites (chemical cues) and resource availability. 3. We performed microcosm experiments with the ciliate model organism Tet-rahymena in order to understand the plasticity of movement strategies with respect to local density while controlling for possible confounding effects mediated by the availability of different cues. In addition, we investigated how an Allee effect can influence movement and dispersal plasticity. 4. Our findings suggest that movement strategies in Tetrahymena are plastic and density-dependent. The observed movement reaction norm was ushaped. This may be due to an Allee effect which led to negative densitydependence at low population densities and generally positive density-dependence at high population densities due to local competition. This possibly adaptive density-dependent movement strategy was likely mediated by chemical cues. 5. Our experimental work in highly controlled conditions indicates that both environmental cues as well as inherent population dynamics must be considered to understand movement and dispersal.

1. 自然种群中几乎所有生物的移动与扩散均为关键生命过程，因此解析其成因与后果具有重要研究价值。现有理论与实证研究均表明，扩散（更确切地说是迁出(emigration)）具有表型可塑性，且可能受局域种群密度调控，但潜在移动策略与种群密度间的功能关系却未得到足够关注。2. 本研究提供了该反应规范(reaction norm)形态的相关证据，并可区分三类潜在调控线索：个体相对数量、代谢物（化学线索(chemical cues)）以及资源可获得性。3. 本研究以纤毛虫模式生物四膜虫(Tetrahymena)为研究对象开展微宇宙实验，旨在解析局域密度梯度下移动策略的表型可塑性，同时控制由不同线索可获得性介导的潜在混淆效应。此外，本研究还探究了阿利效应(Allee effect)如何影响移动与扩散的表型可塑性。4. 研究结果表明，四膜虫的移动策略具有表型可塑性且呈密度依赖特性。观测到的移动反应规范呈现U型分布，这可能源于阿利效应：在种群密度较低时表现为负密度依赖，而在高密度环境下由于局域竞争作用通常呈现正密度依赖。这种可能具有适应性的密度依赖型移动策略，大概率由化学线索介导。5. 本研究在高度可控的实验条件下开展的工作表明，若要解析移动与扩散过程，需同时考虑环境线索与内在种群动态两方面因素。