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.MicrosatGenotypes_Asterionella_formosaExcel spreadsheet of genotypic data of 224 individuals of Asterionella formosa (freshwater diatom), from seven lakes in Switzerland and four lakes in The Netherlands, scored for nine microsatellite markers.AFLP_data_Asterionella_formosaAFLP fingerprint data of 91 isolates of Asterionella formosa (freshwater diatom) at 121 loci, from seven lakes in Switzerland and tree lakes in The Netherlands.Microsatellite sequences Asterionella formosaMicrosatellite sequences of Asterionella formosa, containing the repeat units and forward and reverse primer sites.Microsatellitesequences_Asterionella_formosa.do