Data from: Hidden diversity in the freshwater planktonic diatom Asterionella formosa

Many freshwater and marine algal species are described as having cosmopolitan distributions. Whether these widely distributed morphologically similar algae also share a similar gene pool remains often unclear. In the context of island biogeography theory, stronger spatial isolation deemed typical of freshwater lakes should restrict gene flow and lead to higher genetic differentiation among lakes. Using nine microsatellite loci, we investigate the genetic diversity of a widely distributed freshwater planktonic diatom, Asterionella formosa, across different lakes in Switzerland and the Netherlands. We applied a hierarchical spatial sampling design to determine the geographical scale at which populations are structured. A subset of the isolates was additionally analysed using amplified fragment length polymorphism (AFLP) markers. Our results revealed complex and unexpected population structure in A. formosa with evidence for both restricted and moderate to high gene flow at the same time. Different genetic markers (microsatellites and AFLPs) analysed with a variety of multivariate methods consistently revealed that genetic differentiation within lakes was much stronger than among lakes, indicating the presence of cryptic species within A. formosa. We conclude that the hidden diversity found in this study is expected to have implications for the further use of A. formosa in biogeographical, conservation and ecological studies. Further research using species-level phylogenetic markers is necessary to place the observed differentiation in an evolutionary context of speciation.

诸多淡水与海洋藻类物种被报道具有广布的地理分布范围。然而这些分布广泛、形态相似的藻类是否共享同一基因库，目前仍不明确。基于岛屿生物地理学理论（island biogeography theory），淡水湖泊普遍存在更强的空间隔离效应，这应当会限制基因流，并导致湖泊间更高水平的遗传分化。本研究采用9个微卫星位点（microsatellite loci），对瑞士与荷兰境内不同湖泊中广泛分布的淡水浮游硅藻美丽星杆藻（Asterionella formosa）的遗传多样性展开调查。我们采用分层空间采样方案，以明确种群结构形成的地理尺度。我们还选取部分分离株，采用扩增片段长度多态性（AFLP）标记进行了额外分析。研究结果显示，美丽星杆藻的种群结构复杂且出乎意料：同时存在受限基因流与中等到高强度基因流的现象。采用多种多元统计方法分析不同遗传标记（微卫星与AFLP）后，结果均一致表明：湖泊内部的遗传分化程度远高于湖泊之间，这暗示美丽星杆藻类群中存在隐性物种（cryptic species）。综上，本研究发现的隐秘多样性，有望对后续利用美丽星杆藻开展生物地理学、保护生物学与生态学相关研究产生重要启示。未来需采用物种水平的系统发育标记开展进一步研究，以将本次观测到的遗传分化置于物种形成的进化框架中进行解读。