Niels Daugbjerg

Marine and freshwater cryptophytes are highly valued for their nutritional content and are commonly used as live feed for copepods in aquaculture. Few studies have examined the impact of temperature and salinity on growth rates of several cryptophyte strains isolated from the same water sample. This study presents the first multi-strain autecological analysis of an Arctic marine cryptophyte species, using six strains of Rhodomonas marina and one temperate strain to explore intraspecific variation. Phylogenetic inference based on ITS revealed a close relationship among all R. marina strains (99.6–100 % sequence similarity). The autecological study used batch cultures, examining growth rates at three salinities and five temperatures in one-parameter experiments. One Arctic strain and the temperate strain were also examined at 20.1 and 23.2 °C. All strains grew over a wide range of temperatures and salinities, classifying them as eurythermal and euryhaline. However, the temperate strain exhibited higher phenotypic plasticity concerning temperature, while the Arctic strains showed greater plasticity regarding salinity. Thus, this study identified the presence of intraspecific variation within a confined Arctic marine water mass, highlighting an economic potential when selecting the fastest-growing isolates for biomass production and commercial applications.

Rhodomonas (Cryptophyceae) and species assigned to this genus have undergone numerous taxonomic revisions. This also applies to R. marina studied here as it was originally assigned as a species of Cryptomonas and later considered a variation of R. baltica, the type species. Despite being described more than 130 years ago, R. marina still lacks a comprehensive characterization. Light and electron microscopy were employed to delineate a strain from western Greenland. The living cells were 18 μm long and 9 μm wide, elliptical in shape with a pointed to rounded posterior and truncated anterior in lateral view. Two sub-equal flagella emerged from a vestibulum, where also a furrow extended. In transmission electron microscopy, the furrow was associated with a tubular gullet and the pyrenoid embedded in a deeply lobed chloroplast. The chloroplast contained DNA in perforations and was surrounded by starch grains. A tubular nucleomorph was enclosed within the pyrenoid matrix. In scanning electron microscopy, the inner periplast consisted of rectangular plates with rounded edges and posteriorly these were replaced by a sheet-like structure. The water-soluble pigment was Crypto-Phycoerythrin type I (Cr-PE 545). A phylogenetic inference based on SSU rDNA confirmed the identity of strain S18 as a species of Rhodomonas as it clustered with congeners but also Rhinomonas, Storeatula, and Pyrenomonas. These genera formed a monophyletic clade separated from a diverse assemblage of other cryptophyte genera. To further explore the phylogeny of R. marina a concatenated phylogenetic analysis based on the SSU rDNA-ITS1-5.8S rDNA-ITS2- LSU rDNA region was performed but included only closely related species. The secondary structure of nuclear internal transcribed spacer 2 was predicted and compared to similar structures in related species. Using morphological and molecular signatures as diagnostic features the description of R. marina was emended.

Recent molecular phylogenies that include species of Parvodinium revealed as its closest relatives the genera Peridiniopsis, Palatinus and Johsia. The clade containing these taxa is currently recognized as a family, Peridiniopsidaceae. The affinity between the members of Peridiniopsidaceae cuts across traditional boundaries based on features of the amphiesma, most notably the presence or absence of an apical pore complex. Detailed descriptions of the fine structure of Peridiniopsis and Palatinus are available from TEM studies of their type species. Here we provide a description in comparable detail of a species of the Parvodinium umbonatum–inconspicuum complex, which includes the type of the genus. The cells had an apical fibrous complex essentially similar to those described from other peridinioids prepared with comparable fixations. The pusular system was extensive and included areas with different aspects: an area with a sheet-like vesicle along the mid-right side of the cell, a ventral portion with ramified and anastomosed tubes and a somewhat flattened tube attached to the transverse flagellar canal. The most remarkable feature was the microtubular strand that extended from a ventral, protruding peduncle to the anterior part of the epicone, around an accumulation body, and came around along a more dorsal position toward the ventral side. This long microtubular strand of the peduncle (MSP) was reminiscent of the one described from Peridiniopsis borgei, both by its extension and looping path, and by the breaking up of the strand of microtubules into smaller portions with a wavy appearance; and contrasted with the reduced MSP of Palatinus apiculatus. The fine-structural features currently known from Peridiniopsidaceae are summarized. Members of the family include a flagellar apparatus with four microtubule-containing roots associated, the basal bodies inserted close to each other, nearly at right angles and a three-armed fibrous connective between root 1 and the transverse basal body.

Two strains of peridinioids were isolated from a flooded stream near Aveiro, central Portugal, and examined by light microscopy, scanning electron microscopy and serial-section transmission electron microscopy. The two strains showed the same tabulation and cell shape as Peridiniopsis cunningtonii. One of the strains had lightly reticulated plates and spines in most hypothecal plates, matching the features of typical P. cunningtonii. The other strain showed smooth plates and consistently lacked spines in the apiculate hypotheca. The strains were similar in fine structure and had a central pyrenoid with a starch sheath and perforated by cytoplasmic channels. Details of the flagellar apparatus matched those known from Parvodinium, as did the remarkably long microtubular strand leading to an extruded peduncle that was visible in serial sections. Phylogenetic analyses based on partial LSU rDNA and the concatenated ribosomal operon placed the strain with the smooth hypotheca in a clade with Parvodinium species. The two strains grouped as closely related sister taxa in the partial LSU rDNA phylogeny. A new combination is proposed, Parvodinium cunningtonii comb. nov. and a new variety, Parvodinium cunningtonii var. inerme var. nov., is described.

Nearly two decades ago a scaly quadriflagellate culture was established from a sample collected in Golden Horn Bay, eastern Russia. Here we present a comparative analysis of pheno- and genotypic characters and show that the isolate did not match any existing species of Pyramimonas and is therefore described as P. tatianae sp. nov. The species was probably identified as P. aff. cordata in previous studies on material from the same area. Based on an ultrastructural account of the cell and its external body scales it was found to belong to the subgenus Vestigifera. This was supported by a phylogenetic analysis using the chloroplast-encoded rbcL gene. The cell dimensions of P. tatianae were 6–7 µm long and 5–6 µm wide and it thus represented one of the smaller species of the genus. The cup-shaped chloroplast was divided into four lobes reaching from the middle to the anterior part of the cell. A single posterior eyespot was observed adjacent to an excentric pyrenoid. The ultrastructure of the body and flagellar scales were illustrated from material prepared for whole mounts and thin sections. The new species was compared with P. cordata and P. mitra, two other vestigiferans with which it shares some morphological features. The sequence divergence between P. tatianae and the most closely related species, P. mitra, was 2.5%. The phylogeny of Vestigifera revealed two lineages, one comprising cold-water species and the cosmopolitan P. orientalis, and the other species from temperate-subtropical waters. The tree topology suggested a southbound dispersal route. This was further supported by all antarctic Pyramimonas species having encystment stages as part of their life cycle. It was therefore probable that their ancestors also were capable of producing cysts allowing transportation over great distances. A formal description of the class Pyramimonadophyceae comprising both extant and extinct species was also provided.

Empirical evidence of the cost of producing toxic compounds in harmful microalgae is completely lacking. Yet costs are often assumed to be high, implying substantial ecological benefits with adaptive significance exist. To study potential fitness costs of toxin production, 16 strains including three species of the former Alexandrium tamarense species complex were grown under both carbon limitation and unlimited conditions. Growth rates, levels of intracellular paralytic shellfish toxins (PSTs), and effects of lytic compounds were measured to provide trade-off curves of toxicity for both PST and lytic toxicity under high light (300 μmol photons m⁻² s⁻¹) and under low light (i.e., carbon limited; 20 μmol photons m⁻² s⁻¹). Fitness costs in terms of reduced growth rates with increasing PST content were only evident under unlimited conditions, but not under carbon limitation, in which case PST production was positively correlated with growth. The cost of production of lytic compounds was detected both under carbon limitation and unlimited conditions, but only in strains producing PST. The results may direct future research in understanding the evolutionary role and ecological function of algal toxins. The intrinsic growth rate costs should be accounted for in relation to quantifying benefits such as grazer avoidance or toxin-mediated prey capture in natural food web settings.

SUMMARY: Phalacroma currently comprises 69 species of mostly marine heterotrophic dinophysoids. With a round cell body and short sulcal and cingular lists, Phalacroma spp. have a simple morphology compared to other dinophysoid genera. Therefore, species identification is not always a trivial matter. A few Arctic species have been described and, with the exception of Ph. rotundatum, they are not only infrequently recorded but also occur in low cell abundances. Here, we studied a Lugol fixed sample from Denmark Strait. From this sample 13 cells with a Phalacroma‐like morphology were isolated under a stereo microscope, photo documented, and used for single‐cell PCR determination of nuclear‐encoded LSU rDNA sequences. The sequences fell in three groups defined by their ribotype. A single ribotype sequence representing each group was added to an alignment containing a diverse assemblage of dinophysoids and analyzed using Bayesian analysis and maximum likelihood. Based on comparative light microscopy one of the ribotypes (ribotype 1) was similar but not identical to Ph. ruudi and ribotype 2 could not be matched to a known species of Phalacroma. In the phylogeny both clustered with other species of Phalacroma including the type species. The morphology of ribotype 3 was similar but not identical to Ph. braarudii. In the phylogeny ribotype 3 clustered outside the core group of Phalacroma species. Hence, ribotype 3 was designated ‘Phalacroma’ sp. 3 and has to be described as a new genus pending additional data. This study has revealed the existence of cryptic species diversity within the Phalacroma morphotype boundary. Two additional Phalacroma species (Ph. apicatum and Ph. cf. argus) also clustered outside Phalacroma sensu stricto further emphasizing the presence of cryptic species within the genus. Future studies with a polyphasic approach are needed to better address the taxonomy of Phalacroma and Phalacroma‐like dinophysoids.