硅藻防御：Grazer诱导和增壳成本,Functional Ecology

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硅藻防御：Grazer诱导和增壳成本
Functional Ecology ( IF 4.6 ) Pub Date : 2020-07-31 , DOI: 10.1111/1365-2435.13635
Josephine Grønning ₁ , Thomas Kiørboe ₁

Affiliation

硅藻占海洋初级生产量的40％，并且在海洋封存碳的能力中起着关键作用。硅藻在进化上的成功及其在海洋生物地球化学中的作用与硅质壳有关，硅质壳为草食提供了部分保护。
浮游植物群落的结构和功能受环境限制和有机物权衡的制约。防御机制可能有助于解释海洋中浮游植物（包括硅藻）的高度多样性，但前提是防御必须付出代价。众所周知，在海洋浮游植物中很难证明和量化国防成本。
在这里，我们证明了对于7种浮游硅藻，当细胞暴露于co足类（硅藻的重要捕食者）的化学提示下时，它们的壳变厚，并且其生长速率下降。响应与放牧线索的浓度成正比，但在物种之间和物种内部变化也很大。
在我们的标准实验条件下，典型的增长率下降为10％，而细胞生物二氧化硅的典型增长率为16％。后者的值对应于由于小small足类的放牧死亡率下降了11％。因此，完全有必要对食草动物进行硅化处理。
硅化的成本和收益的数量级相似，表明沿着竞争防御轴的健身态势平坦。这可能有助于解释海洋中共存硅藻的高度多样性。
硅藻对海洋中有机碳的向下通量的显着但可变的贡献在很大程度上取决于细胞中二氧化硅的含量。这较少归因于二氧化硅的压载作用，而主要归因于或多或少受保护的细胞的不同生活史，这些细胞受进化适应和对食草动物的塑性反应所控制（如此处所示）。

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Diatom defence: Grazer induction and cost of shell‐thickening

Diatoms account for 40% of the ocean primary production and play a key role in the oceans’ ability to sequester carbon. The evolutionary success of diatoms and their role in ocean biogeochemistry are related to the siliceous shell that provide partial protection against grazing.
The structure and function of phytoplankton communities are governed by environmental constraints and organismal trade‐offs. Defence mechanisms may help explain the high diversity of phytoplankton (incl. diatoms) in the ocean, but only if the defence comes at a cost. Defence costs have been notoriously difficult to demonstrate and quantify in marine phytoplankton.
Here, we demonstrate for seven species of planktonic diatoms that their shell thickens and their growth rate declines when cells are exposed to chemical cues from copepods, important predators of diatoms. The responses are proportional to the concentration of grazer cues, but are also highly variable, both between and within species.
At our standard experimental condition, the typical decline in growth rate is 10%, and the typical increase in cellular biogenic silica is 16%. The latter value corresponds to a decline in grazing mortality due to small copepods of 11%. Thus, silification in response to grazers is exactly warranted.
The similar magnitude of the costs and benefits of silification suggests a flat fitness landscape along the competition‐defence axis. This may help explain the high diversity of coexisting diatoms in the ocean.
The significant but variable contribution of diatoms to the downward flux of organic carbon in the ocean depends to a large extent on the silica content of the cells. This is due less to the ballasting effect of silica, but mainly to the different life histories of more or less defended cells that are governed by evolutionary adaptations and—as demonstrated here—plastic responses to grazers.

更新日期：2020-07-31

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