Why Do Phytoplankton Evolve Large Size in Response to Grazing?
Why Do Phytoplankton Evolve Large Size in Response to Grazing?
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DOI：
10.1086/706251
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发表时间：
2020-01-01
影响因子：
2.9
通讯作者：
Huisman, Jef
中科院分区：
文献类型：
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作者：
Branco, Pedro;Egas, Martijn;Huisman, Jef
浮游植物是地球上最小的初级生产者之一，但它们的细胞大小却多种多样。通常，小型浮游植物物种比大型浮游植物物种具有更强的营养竞争者，但它们也更容易被吃掉。相比之下，大型浮游植物的进化通常被解释为针对放牧的物理防御。然而，从概念上讲，这种解释是有问题的，因为浮游动物可以共同进化出更大的体型，以应对这种依赖于体型的逃食行为。在这里，我们假设大型浮游植物的进化还有另一个不容易克服的优势：较大的浮游植物通常为浮游动物提供较低的营养质量。我们通过分析生态进化模型来研究这一假设，该模型将浮游植物-浮游动物相互作用的生态化学计量与浮游植物和浮游动物大小的共同进化结合起来。在我们的模型中，细胞大小的进化根据已知的异速生长关系改变了浮游植物的营养吸收动力学，这反过来又影响了浮游植物的营养质量。通过这种基于大小的机制，该模型预测浮游动物的低放牧压力或非选择性放牧有利于高营养质量的小型浮游植物细胞的进化。相比之下，选择性放牧有利于营养质量低的大型浮游植物的进化，而这些浮游植物被中型到大型浮游动物捕食。这种与大小相关的食物质量变化可能解释了常见的现象：从低放牧压力的贫营养水域中的小型超微型浮游植物的优势转向高放牧压力的营养丰富的水域中的大型浮游植物的优势。
Phytoplankton are among the smallest primary producers on Earth, yet they display a wide range of cell sizes. Typically, small phytoplankton species are stronger nutrient competitors than large phytoplankton species, but they are also more easily grazed. In contrast, evolution of large phytoplankton is often explained as a physical defense against grazing. Conceptually, this explanation is problematic, however, because zooplankton can coevolve larger size to counter this size-dependent escape from grazing. Here, we hypothesize that there is another advantage for the evolution of large phytoplankton size not so readily overcome: larger phytoplankton often provide lower nutritional quality for zooplankton. We investigate this hypothesis by analyzing an eco-evolutionary model that combines the ecological stoichiometry of phytoplankton-zooplankton interactions with coevolution of phytoplankton and zooplankton size. In our model, evolution of cell size modifies the nutrient uptake kinetics of phytoplankton according to known allometric relationships, which in turn affect the nutritional quality of phytoplankton. With this size-based mechanism, the model predicts that low grazing pressure or nonselective grazing by zooplankton favors evolution of small phytoplankton cells of high nutritional quality. In contrast, selective grazing for nutritious food favors evolution of large phytoplankton of low nutritional quality, which are preyed on by medium- to large-sized zooplankton. This size-dependent change in food quality may explain the commonly observed shift from dominance by small picophytoplankton in oligotrophic waters with low grazing pressure to large phytoplankton species in nutrient-rich waters with high grazing pressure.