Mixotrophy in nanoflagellates across environmental gradients in the ocean
Mixotrophy in nanoflagellates across environmental gradients in the ocean
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DOI：
10.1073/pnas.1814860116
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发表时间：
2019-03-26
影响因子：
11.1
通讯作者：
Edwards, Kyle F.
中科院分区：
文献类型：
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作者：
Edwards, Kyle F.
混合营养是自养营养和异养营养的结合，是海洋单细胞真核生物的常见营养策略。关于选择混合营养的条件有许多假设，实地研究已经记录了混合营养在各种环境中的流行。然而，目前几乎没有证据表明混合营养如何随环境梯度变化，以及经验模式是否支持理论预测。在这里，我综合了量化光养、混合营养和异养纳米鞭毛虫丰度的实验，以询问混合营养的流行是否存在广泛的模式（相对于纯自养和异养），并询问观察到的模式是否与基于性状的营养策略模型一致。数据表明，在低纬度地区，混合营养生物的丰度增加，而自养生物和异养生物则没有，这可能是由于光可用性的增加所致。在生产力较高的沿海环境中，混合营养生物和自养生物都会大幅增加，而异养生物仅略有增加。这些模式与资源竞争模型一致，其中营养物和碳都可以限制生长，并且混合营养生物在将生物量分配给吞噬功能与自养功能方面经历权衡。重要的是，由于光合作用产生的碳和猎物产生的营养物质之间的协同作用，即使混合营养体因使用通用营养策略而受到惩罚，混合营养体也会在一系列条件下被选择。因此，通过增加辐照度，混合营养相对于专业策略更受青睐，同时增加的营养供应增加了混合营养对异养生物的竞争能力。
Mixotrophy, the combination of autotrophic and heterotrophic nutrition, is a common trophic strategy among unicellular eukaryotes in the ocean. There are a number of hypotheses about the conditions that select for mixotrophy, and field studies have documented the prevalence of mixotrophy in a range of environments. However, there is currently little evidence for how mixotrophy varies across environmental gradients, and whether empirical patterns support theoretical predictions. Here I synthesize experiments that have quantified the abundance of phototrophic, mixotrophic, and heterotrophic nanoflagellates, to ask whether there are broad patterns in the prevalence of mixotrophy (relative to pure autotrophy and heterotrophy), and to ask whether observed patterns are consistent with a trait-based model of trophic strategies. The data suggest that mixotrophs increase in abundance at lower latitudes, while autotrophs and heterotrophs do not, and that this may be driven by increased light availability. Both mixotrophs and autotrophs increase greatly in productive coastal environments, while heterotrophs increase only slightly. These patterns are consistent with a model of resource competition in which nutrients and carbon can both limit growth and mixotrophs experience a trade-off in allocating biomass to phagotrophy vs. autotrophic functions. Importantly, mixotrophy is selected for under a range of conditions even when mixotrophs experience a penalty for using a generalist trophic strategy, due to the synergy between photosynthetically derived carbon and prey-derived nutrients. For this reason mixotrophy is favored relative to specialist strategies by increased irradiance, while at the same time increased nutrient supply increases the competitive ability of mixotrophs against heterotrophs.