| Summary: | International Symposium on Foraminifera (FORAMS 2023), 26-30 June 2023, Perugia, Italy The sequencing of the ribosomal RNA gene of planktonic foraminifera has challenged the morphological species concept since the 1990s when specimens of a single morphospecies showed large divergences among their sequences, indicating the presence of several biological but morphologically cryptic species. Almost three decades of single-cell sequencing carried out by multiple research teams resulted in the publication of ~40 papers and the generation of thousands of single-cell rRNA gene sequences. In addition, the onset of global metabarcoding surveys in the mid-2010s generated a profusion of genetic data that are challenging to align with the first generation data derived of single-cell sequencing. This ultimately renders the global biodiversity assessment of planktonic foraminifera difficult. Here we developed an approach to bring the single-cell and metabarcoding data under the same taxonomic umbrella to assess the worldwide diversity of planktonic foraminifera. We assembled an observational dataset of ~10,000 single-cell foraminifera genetically characterized and queried a global metabarcoding dataset of ~2,000 samples and 2.42 billion reads to retrieve planktonic foraminifera environmental sequences, resulting in ~1100 oceanic stations distributed worldwide. Globally, we identified 94 “biological” species, which nearly doubles the diversity assessment based on exclusively morphological traits. However, our analysis revealed that only 16 morphotaxa carry more than one genotype. This means that the majority of the ~50 morphologically defined species of planktonic foraminifera do not have cryptic diversity. Morphotaxa inhabiting mid to high-latitude environments have the highest degree of cryptic diversity while low-latitude taxa are moderately affected pointing to a non-random distribution of the phenomenon. Overall, our analysis shows that despite a profusion of genetic data, planktonic foraminifera diversity is modest and ...
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