Taxonomic revision of Dictyosiphon (Ectocarpales s.l., Phaeophyceae) from the north-western Pacific, with descriptions of D. asiaticus sp. nov. and D. sparsus sp. nov

ABSTRACT

Dictyosiphon asiaticus sp. nov. and D. sparsus sp. nov. are newly described from Japan and the north-western Pacific. Molecular phylogenies based on the mitochondrial cox1 and cox3 and chloroplast atpB, psaA, psbA and rbcL DNA sequences revealed that Dictyosiphon comprises at least seven lineages worldwide. Japanese Dicytosiphon species formed two clades with high support and were sister to a clade including specimens from the cold-water regions of the northern Pacific, the Arctic, and the north-western Atlantic. Specimens of one of the Japanese clades (= D. asiaticus sp. nov.) were morphologically similar to D. foeniculaceus (generitype described from Scotland, UK), having densely branched thalli with fine branches, and were epiphytic on Scytosiphon spp. and Chordaria spp. Specimens of the other Japanese clade (= D. sparsus sp. nov.) were morphologically similar to D. chordaria, having somewhat thicker, sparse branches with blunt tips, and were epiphytic on Chordaria spp. We assign the third clade distributed on both sides of the North Pacific to D. sinicola, which was described from Washington, USA, for the following reasons: Dictyosiphon specimens in the region having relatively densely branched thalli with fine tips have been identified as D. foeniculaceus, and D. sinicola was distinguished from them by its remarkably larger thallus, while anatomically they are very similar. However, D. foeniculaceus is not widely distributed in the region, with only one genetic lineage (species) reported, so that those two taxa are considered to be ecotypes of the same species, and D. sinicola is the valid name for the taxon.

KEYWORDS:

• Dicytosiphon, D. asiaticus; D. sinicola, D. sparsus, molecular phylogeny, taxonomy

Acknowledgements

We are grateful to Dr Eric Henry for critically reading and improving the manuscript, Dr Sandra Lindstrom for providing specimens, and Drs Poul Møller Pedersen^(†), Bob Hooper and Renato Westermeier for their essential assistance in field collections by AFP.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.1959653

Supplementary fig. S1. Maximum likelihood (ML) molecular phylogeny based on concatenated DNA sequences of mitochondrial cox1 genes (783 bp). Numbers on the branches indicate the bootstrap values (BP, right) and Bayesian posterior probabilities (PP, left). Asterisk (*) indicates 100% BP and 1.00 PP in ML and BI analyses. Only the BP (≥ 70%) and PP (≥ 0.95) are shown.

Supplementary fig. S2. Maximum likelihood (ML) molecular phylogeny based on concatenated DNA sequences of mitochondrial cox1 and cox3 genes (1519 bp). Numbers on the branches indicate the bootstrap values (BP, right) and Bayesian posterior probabilities (PP, left). Asterisk (*) indicates 100% BP and 1.00 PP in ML and BI analyses. Only the BP (≥ 70%) and PP (≥ 0.95) are shown.

Supplementary fig. S3. Maximum likelihood tree based on the concatenated DNA sequences of chloroplast atpB, psaA, psbA and rbcL genes (total 4624 bp). Numbers on branches indicate bootstrap values (%) from ML analysis (left) and posterior probabilities from Bayesian analysis (right). Asterisk (*) indicates 100% bootstrap (ML) and 1.00 posterior probability (Bayesian) values. Only bootstrap values ≥ 70% and posterior probabilities ≥ 0.90 are shown.

Supplementary figs S4–8. Morphology of holotype (UC229735) and isotype (UC98952) specimens of Dictyosiphon tenuis. fig. S4. Opposite branching of the thallus (isotype). figs S5–S7. Surface view showing anatomy of the thallus in different focal planes: large innermost cell (fig. S5, arrowhead); subcortical cells probably derived from the innermost cell (fig. S6, arrowheads); cortical cells probably derived from the subcortical cells (fig. S7, arrowheads). fig. S8. Surface view showing unilocular zoidangia (arrowheads). Note that they are not embedded in the cortical layer. figs S4, S8. UC98952; figs S4–S7. UC229735.

Supplementary table S1. Origin of samples and sequence data used for molecular analyses of chloroplast and mitochondrial genes, including their database accession numbers. Sample codes in [KU-####] correspond to KU-MACC (Kobe University Macroalgal Culture Collection) strain codes, and [KU-d####] corresponds to silica gel dried specimens housed at Kobe University Research Center for Inland Seas. [SAP####] corresponds to herbarium specimens housed at the Hokkaido University. [GWS####] correspond to herbarium/silica gel-dried specimens of Dr G.W. Saunders. Accession codes in bold were newly determined for this study.

Author contributions

H. Kawai: Original concept, collection of specimens, morphological studies, drafting and editing manuscript; T. Hanyuda: genetic analyses; Q. Cheng: genetic analyses; K. A. Miller: collection of specimens and manuscript editing; A. F. Peters: collection of specimens and manuscript editing.

Additional information

Funding

Part of the study was supported by a JSPS Grant-in-Aid for Scientific Research (No. 16H04832) to HK. Collections by AFP in Newfoundland and South America were funded by Newfoundland Institute for Cold Ocean Science and Deutsche Forschungsgemeinschaft (Grant Pe 346/1-1), respectively.