Bisnorgammacerane traces predatory pressure and the persistent rise of algal ecosystems after Snowball Earth
Bisnorgammacerane traces predatory pressure and the persistent rise of algal ecosystems after Snowball Earth
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DOI：
10.1038/s41467-019-08306-x
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发表时间：
2019-01
影响因子：
16.6
通讯作者：
Lennart M. van Maldegem;P. Sansjofre;J. Weijers;K. Wolkenstein;P. Strother;L. Wörmer;J. Hefter;B. N
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文献类型：
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作者：
Lennart M. van Maldegem;P. Sansjofre;J. Weijers;K. Wolkenstein;P. Strother;L. Wörmer;J. Hefter;B. N
真核藻类在新元古代雪球地球冰期后上升到生态相关性，但这种相应的进化过渡的原因仍然是谜。全球范围内的碳酸盐岩都是在这些冰川作用之后直接沉积的，但它们通常是有机贫瘠的或热叠印的。在这里，我们发现，保存完好的盖层白云岩的阿拉拉斯组包含异常丰富的新鉴定的生物标志物：25，28-bisnorgammacerane。它的长期发生，碳同位素系统学和与其他脱甲基萜类化合物的共存表明在细菌占主导地位的生态系统中广泛的微生物降解纤毛虫衍生的生物量的机械连接。下降的25，28-bisnorgammacerane浓度，和平行上升的甾烷对藿烷，表明从细菌到真核生物占主导地位的生态系统的过渡后的马里诺冰川消退。营养水平在低温期已经增加了，这是一个先决条件，但不是藻类增长的最终驱动力。食菌原生生物强烈的捕食压力可能已经清除了自我维持的蓝藻生态系统，从而创造了生态机会，使真核藻类持续上升到全球重要性。
Eukaryotic algae rose to ecological relevance after the Neoproterozoic Snowball Earth glaciations, but the causes for this consequential evolutionary transition remain enigmatic. Cap carbonates were globally deposited directly after these glaciations, but they are usually organic barren or thermally overprinted. Here we show that uniquely-preserved cap dolostones of the Araras Group contain exceptional abundances of a newly identified biomarker: 25,28-bisnorgammacerane. Its secular occurrence, carbon isotope systematics and co-occurrence with other demethylated terpenoids suggest a mechanistic connection to extensive microbial degradation of ciliate-derived biomass in bacterially dominated ecosystems. Declining 25,28-bisnorgammacerane concentrations, and a parallel rise of steranes over hopanes, indicate the transition from a bacterial to eukaryotic dominated ecosystem after the Marinoan deglaciation. Nutrient levels already increased during the Cryogenian and were a prerequisite, but not the ultimate driver for the algal rise. Intense predatory pressure by bacterivorous protists may have irrevocably cleared self-sustaining cyanobacterial ecosystems, thereby creating the ecological opportunity that allowed for the persistent rise of eukaryotic algae to global importance.