Tvärminne Zoological Station, University of Helsinki, Hanko, Finland.
Marine Research Center, Finnish Environment Institute, Helsinki, Finland.
Mol Ecol. 2022 Jan;31(2):512-528. doi: 10.1111/mec.16257. Epub 2021 Nov 11.
Genetic diversity is the basis for evolutionary adaptation and selection under changing environmental conditions. Phytoplankton populations are genotypically diverse, can become genetically differentiated within small spatiotemporal scales and many species form resting stages. Resting stage accumulations in sediments (seed banks) are expected to serve as reservoirs for genetic information, but so far their role in maintaining phytoplankton diversity and in evolution has remained unclear. In this study we used the toxic dinoflagellate Alexandrium ostenfeldii (Dinophyceae) as a model organism to investigate if (i) the benthic seed bank is more diverse than the pelagic population and (ii) the pelagic population is seasonally differentiated. Resting stages (benthic) and plankton (pelagic) samples were collected at a coastal bloom site in the Baltic Sea, followed by cell isolation and genotyping using microsatellite markers (MS) and restriction site associated DNA sequencing (RAD). High clonal diversity (98%-100%) combined with intermediate to low gene diversity (0.58-0.03, depending on the marker) was found. Surprisingly, the benthic and pelagic fractions of the population were equally diverse, and the pelagic fraction was temporally homogeneous, despite seasonal fluctuation of environmental selection pressures. The results of this study suggest that continuous benthic-pelagic coupling, combined with frequent sexual reproduction, as indicated by persistent linkage equilibrium, prevent the dominance of single clonal lineages in a dynamic environment. Both processes harmonize the pelagic with the benthic population and thus prevent seasonal population differentiation. At the same time, frequent sexual reproduction and benthic-pelagic coupling maintain high clonal diversity in both habitats.
遗传多样性是生物在不断变化的环境条件下进行进化适应和选择的基础。浮游植物种群在基因型上具有多样性，可以在小的时空尺度内发生遗传分化，并且许多物种形成休眠阶段。休眠阶段在沉积物（种子库）中的积累预计将作为遗传信息的储存库，但迄今为止，它们在维持浮游植物多样性和进化中的作用仍不清楚。在这项研究中，我们以有毒甲藻亚历山大藻（Dinophyceae）为模型生物，研究了以下两个问题：（i）底栖种子库是否比浮游种群更具多样性；（ii）浮游种群是否存在季节性分化。在波罗的海的一个沿海繁殖地采集了休眠阶段（底栖）和浮游（浮游）样本，然后使用微卫星标记（MS）和限制位点相关 DNA 测序（RAD）进行细胞分离和基因分型。结果发现，高克隆多样性（98%-100%）与中等至低基因多样性（取决于标记，0.58-0.03）相结合。令人惊讶的是，尽管环境选择压力存在季节性波动，但底栖和浮游种群的组成部分同样具有多样性，并且浮游种群在时间上是同质的。这项研究的结果表明，持续的底栖-浮游耦合，加上频繁的有性繁殖，如持续的连锁平衡所表明的那样，防止了单一克隆谱系在动态环境中的主导地位。这两个过程协调了浮游种群和底栖种群，从而防止了季节性的种群分化。同时，频繁的有性繁殖和底栖-浮游耦合在两个栖息地中维持了高克隆多样性。
