• The development of calcification by the coccolithophores had a profound impact on ocean carbon cycling, but the evolutionary steps leading to the formation of these complex biomineralized structures are not clear. Heterococcoliths consisting of intricately shaped calcite crystals are formed intracellularly by the diploid life cycle phase. Holococcoliths consisting of simple rhombic crystals can be produced by the haploid life cycle stage but are thought to be formed extracellularly, representing an independent evolutionary origin of calcification.
• We use advanced microscopy techniques to determine the nature of coccolith formation and complex crystal formation in coccolithophore life cycle stages.
• We find that holococcoliths are formed in intracellular compartments in a similar manner to heterococcoliths. However, we show that silicon is not required for holococcolith formation and that the requirement for silicon in certain coccolithophore species relates specifically to the process of crystal morphogenesis in heterococcoliths.
• We therefore propose an evolutionary scheme in which the lower complexity holococcoliths represent an ancestral form of calcification in coccolithophores. The subsequent recruitment of a silicon-dependent mechanism for crystal morphogenesis in the diploid life cycle stage led to the emergence of the intricately shaped heterococcoliths, enabling the formation of the elaborate coccospheres that underpin the ecological success of coccolithophores.

中文翻译：

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硅在球石藻复杂晶体形状发展中的作用

• 球石藻钙化的发展对海洋碳循环产生了深远的影响，但导致这些复杂生物矿化结构形成的进化步骤尚不清楚。由形状复杂的方解石晶体组成的杂球藻是通过二倍体生命周期阶段在细胞内形成的。由简单的菱形晶体组成的全球藻可以在单倍体生命周期阶段产生，但被认为是在细胞外形成的，代表钙化的独立进化起源。
• 我们使用先进的显微镜技术来确定在球石藻生命周期阶段中球石形成和复杂晶体形成的性质。
• 我们发现 holococcoliths 在细胞内的隔室中形成的方式与异粒虫类似。然而，我们表明，硅不是 holococcolith 形成所必需的，并且某些颗石藻物种对硅的需求与异颗石中晶体形态发生的过程特别相关。
• 因此，我们提出了一种进化方案，其中较低复杂性的 holococcoliths 代表了球石藻中钙化的祖先形式。随后在二倍体生命周期阶段对晶体形态发生的硅依赖性机制的补充导致了形状复杂的杂球石的出现，从而形成了支撑球石藻生态成功的复杂球球。