BACKGROUND The ocean microbiota modulates global biogeochemical cycles and changes in its configuration may have large-scale consequences. Yet, the underlying ecological mechanisms structuring it are unclear. Here, we investigate how fundamental ecological mechanisms (selection, dispersal and ecological drift) shape the smallest members of the tropical and subtropical surface-ocean microbiota: prokaryotes and minute eukaryotes (picoeukaryotes). Furthermore, we investigate the agents exerting abiotic selection on this assemblage as well as the spatial patterns emerging from the action of ecological mechanisms. To explore this, we analysed the composition of surface-ocean prokaryotic and picoeukaryotic communities using DNA-sequence data (16S- and 18S-rRNA genes) collected during the circumglobal expeditions Malaspina-2010 and TARA-Oceans. RESULTS We found that the two main components of the tropical and subtropical surface-ocean microbiota, prokaryotes and picoeukaryotes, appear to be structured by different ecological mechanisms. Picoeukaryotic communities were predominantly structured by dispersal-limitation, while prokaryotic counterparts appeared to be shaped by the combined action of dispersal-limitation, selection and drift. Temperature-driven selection appeared as a major factor, out of a few selected factors, influencing species co-occurrence networks in prokaryotes but not in picoeukaryotes, indicating that association patterns may contribute to understand ocean microbiota structure and response to selection. Other measured abiotic variables seemed to have limited selective effects on community structure in the tropical and subtropical ocean. Picoeukaryotes displayed a higher spatial differentiation between communities and a higher distance decay when compared to prokaryotes, consistent with a scenario of higher dispersal limitation in the former after considering environmental heterogeneity. Lastly, random dynamics or drift seemed to have a more important role in structuring prokaryotic communities than picoeukaryotic counterparts. CONCLUSIONS The differential action of ecological mechanisms seems to cause contrasting biogeography, in the tropical and subtropical ocean, among the smallest surface plankton, prokaryotes and picoeukaryotes. This suggests that the idiosyncrasy of the main constituents of the ocean microbiota should be considered in order to understand its current and future configuration, which is especially relevant in a context of global change, where the reaction of surface ocean plankton to temperature increase is still unclear. Video Abstract.

中文翻译：

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解开形成表层海洋微生物群的机制。

背景技术海洋微生物群调节全球生物地球化学循环，其构造的变化可能具有大规模的后果。然而，构成它的潜在生态机制尚不清楚。在这里，我们研究了基本的生态机制（选择，扩散和生态漂移）如何塑造热带和亚热带表面海洋微生物群落的最小成员：原核生物和微小的真核生物（picoeukaryotes）。此外，我们调查了对这种组合以及从生态机制的作用中出现的空间格局发挥非生物选择作用的因子。为了探索这一点，我们使用环行全球探险活动Malaspina-2010和TARA-Ocean收集的DNA序列数据（16S和18S-rRNA基因），分析了表面海洋原核和微核生物群落的组成。结果我们发现，热带和亚热带表面海洋微生物区系的两个主要成分，原核生物和微核生物，似乎是由不同的生态机制构成的。皮原核生物群落主要由分散限制构成，而原核对应物似乎由分散限制，选择和漂移共同作用形成。在少数几个选择的因素中，温度驱动的选择似乎是一个主要因素，它影响原核生物而不是皮真核生物的物种共现网络，这表明关联模式可能有助于理解海洋微生物群的结构和对选择的反应。其他测量的非生物变量似乎对热带和亚热带海洋的群落结构具有有限的选择性影响。与原核生物相比，微型真核生物在群落之间表现出更高的空间分异性，并且距离衰减程度更高，这与考虑环境异质性的前者更高的扩散限制情况一致。最后，随机动力学或漂移似乎在构造原核生物群落中比在真核生物中更为重要。结论在热带和亚热带海洋中，在最小的浮游生物，原核生物和微核生物中，生态机制的差异作用似乎引起了生物地理学上的对比。这表明，应考虑海洋微生物群主要成分的特质，以便了解其当前和未来的结构，这在全球变化的背景下尤其重要，尚不清楚海洋浮游生物对温度升高的反应。录像摘要。