Abstract
Most research on extant planktonic foraminifera has been directed towards larger species (>0.150 mm) which can be easily manipulated, counted and yield enough calcite for geochemical analyses. This has drawn attention towards the macroperforate clade and created an impression of their numerical and ecological dominance. Drawing such conclusions from the study of such “giants” is a dangerous path. There were times in the evolutionary history of planktonic foraminifera when all species were smaller than 0.1 mm and indeed numerous small taxa, mainly from the microperforate clade, have been formally described from the modern plankton. The significance of these small, obscure and neglected species is poorly characterized and their relationship to the newly discovered hyperabundant but uncharacterized lineages of planktonic foraminifera in metabarcoding datasets is unknown. To determine, who is hiding in the metabarcoding datasets, we carried out an extensive sequencing of 18S rDNA targeted at small and obscure species. The sequences of the newly characterized small and obscure taxa match many of the previously uncharacterized lineages found in metabarcoding data. This indicates that most of the modern diversity in planktonic foraminifera has been taxonomically captured, but the role of the small and neglected taxa has been severely underestimated.
Highlights
Planktonic foraminifera are characterized by a modest diversity of ~50 morphologically defined species traditionally assigned to four clades [1,2]
Since the diversity of planktonic foraminifera is based on diagnostic characters of their calcite shells, and the barcoding effort covered all of the abundant lineages, it was assumed that barcode sequences from environmental samples would be assigned to the existing taxonomic backbone
We still cannot characterize all the environmental Operational Taxonomic Units (OTUs), we show that by adding only five additional morphological species to our barcode catalog and extending the coverage in the microperforate clade allowed us to reduce the unassigned diversity in the environmental dataset from Morard et al [4] from almost half to less than one fifth and the number of reads associated with the unassigned diversity from 43% to mere 11% (Fig 6)
Summary
Planktonic foraminifera are characterized by a modest diversity of ~50 morphologically defined species traditionally assigned to four clades [1,2]. Since the diversity of planktonic foraminifera is based on diagnostic characters of their calcite shells, and the barcoding effort covered all of the abundant lineages, it was assumed that barcode sequences from environmental samples would be assigned to the existing taxonomic backbone. It came as a surprise when the first metabarcoding survey [4] revealed abundant lineages of foraminifera occurring in small size fractions of the plankton that did not fit into the existing taxonomic. Is it possible that taxonomers working on the plankton for over a century completely missed apparently abundant taxa? Could there be planktonic foraminifera that escaped detection because they lost their shell? Or, could it be that we have underestimated the role and diversity among the taxa for which we have not yet generated barcodes? Perhaps, the taxa that are not yet genetically characterized are not just variants of the existing diversity, but represent, unexpectedly, distinct lineages?
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
