A taxonomic review of the genus Phaeocystis

Abstract

Phaeocystis is recognized both as a nuisance and as an ecologically important phytoplankton species. Its polymorphic life cycle with both colonial and Xagellated cells causes many taxonomic problems. Sequence variation among 22 isolates representing a global distribution of the genus has been compared using three molecular markers. The ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) spacer is too conserved to resolve species. The most conserved 18S ribosomal deoxyribonucleic acid (rDNA) analysis suggests that an undescribed unicellular Phaeocystis sp. (isolate PLY559) is a sister taxon to the Mediterranean unicellular Phaeocystis jahnii; this clade branched prior to the divergence of all other Phaeocystis species, including the colonial ones. The internal transcribed spacer (ITS) region shows suYcient variation that some spatial population structure can be recovered, at least in P. antarctica. P. globosa and P. pouchetii have multiple diVerent ITS copies, suggestive of cryptic species that are still able to hybridize. A molecular clock has been constructed that estimates the divergence of the cold water colonial forms from the warm-water colonial forms to be about 30 Ma and the divergence of P. antarctica and P. pouchetii to be about 15 Ma. A short description of the colonial stage and the Xagellated stage for each formally recognized species is provided. Morphological information is also provided on a number of undescribed species. These include the strain Ply 559, consisting of non-colonial cells with peculiar tubular extrusomes, a second non-colonial species from the north western Mediterranean Sea producing a lot of mucus, and a colonial species with scale-less Xagellates found in Italian waters. In addition, three Xagellated morphotypes with scales diVerent from those of P. antarctica were reported in the literature from Antarctic waters. The picture emerging from both molecular and morphological data is that the number of species in the genus is still underestimated and that cryptic or pseudocryptic diversity requires a sound assessment in future research of this genus. Based on all published observations, an emended description of the genus is provided.

Haptophyte Diversity and Vertical Distribution Explored by 18S and 28S RibosomalRNAGene Metabarcoding and Scanning Electron Microscopy

“…Of the most OTU‐rich groups, the group with the highest proportion of OTUs matching environmental sequences was Phaeocystaceae and Chrysochromulinaceae (Table S4a). Within both of these groups, several morphological forms have been recognized that are not yet in culture and genetically characterized (Jensen ; Medlin and Zingone ). Our result, that several OTUs had best match with DNA sequences or reads from environmental samples, supports previous studies showing that there is a large diversity of haptophytes that remains to be cultured and DNA sequence determined (e.g.…”

Intraspecific variability in Phaeocystis antarctica's response to iron and light stress

“…antarctica has different biogeographical ecotypes [30, 31] and it was recently shown that the species’ genetic variability is high over space and time, even among clones isolated from the same P . antarctica bloom [29].…”

CRYPTIC AND PSEUDO‐CRYPTIC DIVERSITY IN DIATOMS—WITH DESCRIPTIONS OF PSEUDO‐NITZSCHIA HASLEANA SP. NOV. AND P. FRYXELLIANA SP. NOV.1

“…2005, Boenigk et al. 2006, Medlin and Zingone 2007). In an evolutionary context, cryptic and pseudo‐cryptic species may represent species that (i) have not evolved evident morphological differences because there is no selective pressures on morphology (Bickford et al.…”