https://orcid.org/0000-0002-7850-6031
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ABSTRACT
Fragilariaceae is a paraphyletic family of araphid diatoms commonly used as bio-indicators, in environmental assessments and in paleoenvironmental reconstructions, and with various potential industrial applications. Recent molecular taxonomic research has highlighted significant limitations in traditional morphology-based investigations of these diatom species. Most descriptions of species and genera of the Fragilariaceae present broad morphological character definitions and many diagnostic characters are indistinguishable by light microscopy. In this sense, taxon misidentification is common and could have serious implications for environmental surveys and laboratory experiments. To better understand the diversity of the Fragilariaceae, we (1) performed phylogenetic analyses of the small subunit ribosomal RNA (18S rRNA), rbcL and psbC gene sequences, (2) inferred a cladogram from key morphological features used in the traditional identification of Fragilariaceae, (3) tested if the topologies of the tree recovered from the molecular phylogeny, of the tree based on morphology and of the trees constraining to monophyly the genera Sarcophagodes, Pseudostaurosira and Nanofrustulum (together and separately) were significantly different and (4) mapped morphological character states on the ML tree and inferred their evolution based on maximum parsimony. Our results supported the monophyly of a group of Fragilariaceae within small araphid diatoms including the genera Cratericulifera, Plagiostriata, Castoridens, Opephora, Staurosira, Staurosirella, Punctastriata, Psammotaenia, Hendeyella, Stauroforma, Pseudostaurosira sensu Li, Nanofrustulum sensu Li, Serratifera sensu Li and Gedaniella sensu Li. Molecular phylogeny and topology tests suggested that the latest circumscriptions of the genera Sarcophagodes, Pseudostaurosira and Nanofrustulum sensu Morales were not monophyletic. Analyses of the Antarctic strain IMA070A collected during the XXXIV Italian Antarctic Expedition using fine structural features of the frustule and molecular data revealed that this diatom belongs to a distinct lineage within Gedaniella, which we describe here as Gedaniella antarctica sp. nov.
Highlights
Fragilariaceae diversity was revealed combining molecular data and morphology.
Fragilariaceae displayed cryptic diversity.
Gedaniella antarctica represent a new araphid diatom from Antarctica.
Acknowledgements
We wish to thank Dr Federico Zorzi (CEASC, Center for Analyses and Certification Services, University of Padova) for his assistance with the SEM analysis.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary material
The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2024.2366340
Supplementary table S1: Voucher identity and GenBank accession numbers for the taxa used in the DNA dataset. GenBank accession numbers listed in order: 18S rDNA, rbcL and psbC.
Supplementary table S2: Results of topology test. Scores of constrained trees: (BMOL) = ML unconstrained tree using molecular data, (SAR) = Sarcophagodes sensu Morales, (PSE) = Pseudostaurosira sensu Morales, (NAN) = Nanofrustulum sensu Morales, (SAR+PSE+NAN) = Sarcophagodes, Pseudostaurosira and Nanofrustulum sensu Morales and (BMORPH) = ML unconstrained tree using morphological data + = 95% confidence. − = significant exclusion. All tests performed 10 000 resamplings using the RELL method.
1deltaL: logL difference from the maximal logl in the set. 2bp–RELL: bootstrap proportion using RELL method (Kishino et al. 1990). 3p–KH: p–value of one–sided Kishino–Hasegawa test (1989). 4p–SH: p–value of Shimodaira–Hasegawa test (2000). 5p–WKH: p–value of weighted KH test. 6p–WSH: p–value of weighted SH test. 7c–ELW: Expected likelihood weight (Strimmer & Rambaut Citation2002). 8p–AU: p–value of approximately unbiased (AU) test.
Supplementary table S3: Morphological characters of small araphid diatoms belonging to the monophyletic Fragilariaceae.
Supplementary table S4: Characters and their states used in the phylogenetic analysis.
Supplementary table S5: Phylogenetic signal for each character. Including: δ–values, random δ–values, and p–values and significance codes: (p < 0.05 ‘*’), (0.05 ≤ p < 0.1 ‘•’), (p ≥ 0.1 ‘n.s.’).
Supplementary fig. S1: Maximum likelihood (ML) phylogeny of the concatenated 18S rDNA, rbcL and psbC focusing on Gedaniella genus. Approximate likelihood ratio tests based on Shimodaira–Hasegawa‐like procedures (SH‐aLRT) values (%), Bayesian posterior probabilities (PP) and ML bootstrap values (%) are shown above branches (SH‐aLRT supports ≥ 80%, posterior probabilities ≥ 0.70 and bootstrap values ≥ 50%).
Data availability statement
The 18S rRNA, rbcL and psbC gene sequences have been submitted to GenBank (accession numbers: OR162449, OR166366 and OR166367, respectively). The data that support the findings of this study (concatenated 18S rDNA, rbcL and psbC sequence alignment, ‘.fasta’ format, and morphological matrix, ‘.nexus’ format) are available from the corresponding author [I. Moro], upon reasonable request.
Author contributions
R. Trentin: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing – original draft; E. Moschin: Data curation, Formal analysis, Investigation, Validation, Writing – review & editing; S. Schiaparelli: Funding acquisition, Writing – review & editing; I. Moro: Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Resources, Supervision, Validation, Visualization, Writing – review & editing.