Diatoms are the most recent major algal lineage added to the geological record, appearing more than 200 million years ago. They are stramenopile protists resulting from a secondary endosymbiotic event that yielded the only photosynthetic protistan lineage expressing external siliceous cell wall structures called frustules. Many diatoms also have large internal vacuoles, and a common assumption in the literature is that success of the diatoms is largely attributable to these two morphological inventions: the frustule for defense and vacuole for luxury nutrient uptake. Here, we revisit the evolution of these inventions, propose sequential steps in frustule development, replace luxury nutrient uptake with predator defense and buoyancy control as the driver of vacuole expansion, and suggest that perhaps the greatest significance of the frustule for diatom evolution is the secondary consequence of enhancing sexual reproduction. In this synthesis, we emphasize a distinction between the “general” success of diatoms and the success of “bloom-forming” species, as the physiological and morphological drivers of these successes differ. Importantly, the bloom-forming species are responsible for the major role of diatoms in aquatic biogeochemical cycles. The bloom-forming habit we ascribe to specific physiological attributes that, at their core, revolve around influencing the balance between diatom growth and losses to predators. We propose that these physiological adaptations are linked to size-dependent maximum division rates in bloom-forming diatoms, because of size scaling of predator–prey interactions. The existence of these bloom-forming species yields an apparent allometric relationship that has previously been interpreted in terms of nutrient acquisition. Our analysis yields insights into species successions during blooms, considers the fundamental benefit of blooming (and subsequent sinking) from a reproductive standpoint, and provides some reinterpretation of diatoms success over geologic time and in the modern ocean.

中文翻译：

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硅藻演化与生态位的思考

硅藻是地质记录中最新添加的主要藻类谱系，出现于 2 亿多年前。它们是原生藻菌原生生物，由二次内共生事件产生，产生唯一的光合原生生物谱系，表达称为硅藻壳的外部硅质细胞壁结构。许多硅藻也有很大的内部液泡，文献中的一个普遍假设是，硅藻的成功很大程度上归功于这两个形态发明：用于防御的硅藻壳和用于奢侈营养吸收的液泡。在这里，我们重新审视了这些发明的演变，提出了藻壳发育的连续步骤，用捕食者防御和浮力控制取代了奢侈的营养吸收，作为液泡扩张的驱动力，并建议硅藻进化的硅藻壳的最大意义可能是增强有性繁殖的次要结果。在此综合中，我们强调硅藻的“一般”成功与“开花形成”物种的成功之间的区别，因为这些成功的生理和形态驱动因素不同。重要的是，形成水华的物种负责硅藻在水生生物地球化学循环中的主要作用。我们归因于特定生理属性的开花形成习惯，其核心是影响硅藻生长和捕食者损失之间的平衡。我们提出，由于捕食者-猎物相互作用的大小缩放，这些生理适应与形成水华的硅藻中依赖于大小的最大分裂率有关。这些形成花朵的物种的存在产生了一种明显的异速生长关系，之前已根据养分获取对其进行了解释。我们的分析产生了对开花期间物种演替的见解，从繁殖的角度考虑了开花（和随后下沉）的基本好处，并提供了对地质时间和现代海洋中硅藻成功的一些重新解释。