Sorbonne Université, CNRS, UMR7144 Adaptation et Diversité en Milieu Marin, Ecology of Marine Plankton (ECOMAP), Station Biologique de Roscoff SBR, 29680, Roscoff, France.
Sorbonne Université, CNRS, FR2424 ABIMS, Station Biologique de Roscoff SBR, 29680, Roscoff, France.
Sci Rep. 2020 Feb 13;10(1):2531. doi: 10.1038/s41598-020-59524-z.
As critical primary producers and recyclers of organic matter, the diversity of marine protists has been extensively explored by high-throughput barcode sequencing. However, classification of short metabarcoding sequences into traditional taxonomic units is not trivial, especially for lineages mainly known by their genetic fingerprints. This is the case for the widespread Amoebophrya ceratii species complex, parasites of their dinoflagellate congeners. We used genetic and phenotypic characters, applied to 119 Amoebophrya individuals sampled from the same geographic area, to construct practical guidelines for species delineation that could be applied in DNA/RNA based diversity analyses. Based on the internal transcribed spacer (ITS) regions, ITS2 compensatory base changes (CBC) and genome k-mer comparisons, we unambiguously defined eight cryptic species among closely related ribotypes that differed by less than 97% sequence identity in their SSU rDNA. We then followed the genetic signatures of these parasitic species during a three-year survey of Alexandrium minutum blooms. We showed that these cryptic Amoebophrya species co-occurred and shared the same ecological niche. We also observed a maximal ecological fitness for parasites having narrow to intermediate host ranges, reflecting a high cost for infecting a broader host range. This study suggests that a complete taxonomic revision of these parasitic dinoflagellates is long overdue to understand their diversity and ecological role in the marine plankton.
作为关键的初级生产者和有机物的再循环者，海洋原生生物的多样性已经通过高通量条码测序得到了广泛的探索。然而，将短的代谢条形码序列分类为传统的分类单元并不简单，特别是对于主要通过其遗传指纹来识别的谱系。广泛存在的 Amoebophrya ceratii 物种复合体就是这种情况，它是其甲藻同类的寄生虫。我们使用遗传和表型特征，对从同一地理区域采样的 119 个 Amoebophrya 个体进行了研究，构建了用于物种划分的实用指南，这些指南可应用于基于 DNA/RNA 的多样性分析。基于内部转录间隔区（ITS）区域、ITS2 补偿碱基变化（CBC）和基因组 k-mer 比较，我们在近缘核糖体 DNA 序列同一性小于 97%的情况下，明确定义了 8 个隐种。然后，我们在对亚历山大藻微囊藻爆发的为期三年的调查中跟踪了这些寄生物种的遗传特征。我们表明，这些隐生的 Amoebophrya 物种共同存在并共享相同的生态位。我们还观察到寄生范围狭窄到中等的寄生虫具有最大的生态适应性，这反映出感染更广泛的宿主范围的高成本。这项研究表明，对这些寄生甲藻进行全面的分类修订是理解它们在海洋浮游生物中的多样性和生态作用的当务之急。
