Annenkova Nataliia V, Giner Caterina R, Logares Ramiro
Limnological Institute Siberian Branch of the Russian Academy of Sciences 3, Ulan-Batorskaya St., 664033 Irkutsk, Russia.
Institute of Marine Sciences (ICM), CSIC, Passeig Marítim de la Barceloneta, 37-49, ES08003 Barcelona, Spain.
Microorganisms. 2020 Apr 9;8(4):543. doi: 10.3390/microorganisms8040543.
Ancient lakes are among the most interesting models for evolution studies because their biodiversity is the result of a complex combination of migration and speciation. Here, we investigate the origin of single celled planktonic eukaryotes from the oldest lake in the world-Lake Baikal (Russia). By using 18S rDNA metabarcoding, we recovered 1414 Operational Taxonomic Units (OTUs) belonging to protists populating surface waters (1-50 m) and representing pico/nano-sized cells. The recovered communities resembled other lacustrine freshwater assemblages found elsewhere, especially the taxonomically unclassified protists. However, our results suggest that a fraction of Baikal protists could belong to glacial relicts and have close relationships with marine/brackish species. Moreover, our results suggest that rapid radiation may have occurred among some protist taxa, partially mirroring what was already shown for multicellular organisms in Lake Baikal. We found 16% of the OTUs belonging to potential species flocks in Stramenopiles, Alveolata, Opisthokonta, Archaeplastida, Rhizaria, and Hacrobia. Putative flocks predominated in Chrysophytes, which are highly diverse in Lake Baikal. Also, the 18S rDNA of a number of species (7% of the total) differed >10% from other known sequences. These taxa as well as those belonging to the flocks may be endemic to Lake Baikal. Overall, our study points to novel diversity of planktonic protists in Lake Baikal, some of which may have emerged in situ after evolutionary diversification.
古代湖泊是进化研究中最有趣的模型之一，因为它们的生物多样性是迁移和物种形成复杂组合的结果。在这里，我们研究了世界上最古老的湖泊——俄罗斯贝加尔湖中的单细胞浮游真核生物的起源。通过使用18S rDNA代谢条形码技术，我们获得了1414个操作分类单元（OTU），它们属于生活在表层水（1 - 50米）中的原生生物，代表了微微型/微型细胞。所恢复的群落类似于在其他地方发现的其他湖泊淡水组合，特别是那些分类学上未分类的原生生物。然而，我们的结果表明，贝加尔湖的一部分原生生物可能属于冰川遗迹，并且与海洋/咸淡水物种有密切关系。此外，我们的结果表明，一些原生生物类群可能发生了快速辐射，部分反映了贝加尔湖多细胞生物已经显示出的情况。我们发现16%的OTU属于不等鞭毛类、囊泡虫类、后鞭毛生物、原始色素体生物、根足虫类和Hacrobia中的潜在物种群。假定的物种群在金藻门中占主导地位，金藻门在贝加尔湖高度多样化。此外，一些物种（占总数的7%）的18S rDNA与其他已知序列的差异>10%。这些分类群以及属于物种群的分类群可能是贝加尔湖特有的。总体而言，我们的研究指出了贝加尔湖浮游原生生物的新多样性，其中一些可能是在进化多样化后原地出现的。
