Size and shape profoundly influence an organism's ecophysiological performance and evolutionary fitness, suggesting a link between morphology and diversity. However, not much is known about how body shape is related to taxonomic richness, especially in microbes. Here we analyse global datasets of unicellular marine phytoplankton, a major group of primary producers with an exceptional diversity of cell sizes and shapes and, additionally, heterotrophic protists. Using two measures of cell shape elongation, we quantify taxonomic diversity as a function of cell size and shape. We find that cells of intermediate volume have the greatest shape variation, from oblate to extremely elongated forms, while small and large cells are mostly compact (e.g., spherical or cubic). Taxonomic diversity is strongly related to cell elongation and cell volume, together explaining up to 92% of total variance. Taxonomic diversity decays exponentially with cell elongation and displays a log-normal dependence on cell volume, peaking for intermediate-volume cells with compact shapes. These previously unreported broad patterns in phytoplankton diversity reveal selective pressures and ecophysiological constraints on the geometry of phytoplankton cells which may improve our understanding of marine ecology and the evolutionary rules of life.

中文翻译：

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形状很重要：浮游植物细胞几何形状与多样性之间的关系

大小和形状深刻影响生物体的生态生理性能和进化适应性，表明形态与多样性之间存在联系。但是，人们对人体形状与生物分类丰富性之间的关系知之甚少，尤其是在微生物中。在这里，我们分析了单细胞海洋浮游植物的全球数据集，这是一类主要的主要生产者，其细胞大小和形状以及异养原生生物异常丰富。使用细胞形状伸长的两种度量，我们将分类学多样性量化为细胞大小和形状的函数。我们发现，中等体积的单元格具有最大的形状变化，从扁圆形到极长的形式，而小型和大型单元格大多是紧凑的（例如球形或立方）。分类学多样性与细胞伸长率和细胞体积密切相关，一起解释高达92％的总方差。分类学多样性随细胞伸长呈指数衰减，并且对细胞体积显示出对数正态依赖性，对于形状紧凑的中等体积细胞则达到峰值。这些以前未报道的浮游植物多样性的广泛模式揭示了浮游植物细胞几何结构的选择性压力和生态生理约束，这可能会增进我们对海洋生态学和生命进化规则的理解。