Ulvophycean Algae Research Articles

Characteristics of mitosis in the gametophyte cells of the marine green alga Monostroma angicava

BackgroundSome marine algae exhibit several characteristics of mitosis (e.g., the timing of mitosis such as diurnal periodicity) that are unique from those of land plants. Not only the timing but also other characteristics of mitosis, including the process itself and the number of chromosomes involved, are largely unknown in ulvophycean marine green algae. Effective mitotic inhibitors are useful for observing mitosis and identifying the number of chromosomes. However, few such inhibitors are available for ulvophycean algae. Here, we examined the timing and process of mitosis and the number of chromosomes with several mitotic inhibitors in the haploid gametophyte cells of the Ulvophyceae alga Monostroma angicava.ResultsMitosis did not occur during the light period but began immediately after the onset of the dark period. The typical process of mitosis was observed. The mitotic inhibitors colchicine and 8-hydroxyquinoline, which generally arrest mitosis in land plants, were ineffective in M. angicava. We found that three other mitotic inhibitors, amiprophos methyl, griseofulvin and oryzalin, are effective to arrest mitosis. With three-dimensional fluorescence microscopy, we demonstrated that there were nine chromosomes in each cell.ConclusionsIn the gametophyte cells of M. angicava, mitosis occurs diurnally. It is triggered by the onset of the dark period. We identified the number of chromosomes as N = 9. Our study shows effective inhibitors to observe mitosis in ulvophycean algae.

Ochlochaete incrustans sp. nov., a new species of freshwater ulvophycean algae from California, USA, with notes on Friedaea torrenticola

:During a broad survey of the stream algae of California, a rare and unusual green alga was encountered. Samples were collected in three sites, one 200 m from a stream outlet into the Pacific Ocean and the others 6–20 km inland from the ocean. We initially identified the alga as Friedaea torrenticola Schmidle, which had been previously reported from California by G.M. Smith in 1933. However, additional observations and analysis led us to conclude that the specimen represented a new species of the primarily marine genus Ochlochaete. Ochlochaete incrustans sp. nov. grows in dense, lime-encrusted mats in fast-flowing streams. The thallus is a branched filament terminating in slightly clavate cells. Some intercalary cells are furnished with long, colourless setae. Transmission electron microscopic analysis revealed that the pyrenoid is traversed by a single, straight thylakoid similar to the ulvophycean alga Phaeophila. Molecular phylogenetic analysis of the new species based on the nuclear-encoded 18S rDNA and chloroplast-encoded tufA gene sequences revealed that it is most closely related to Ochlochaete hystrix Thwaites (Ulvaceae, Ulvophyceae).

Phylogenetic Position and Morphological Observation of the Ctenocladus circinnatus Borzi, a rare green alga from Changtang Plateau, China

Two microfilamentous green algal specimens from Tibet were identified as Ctenocladus circinnatus Borzi, due to their unique morphology and saline habitat. The phylogenetic evidence based on DNA sequence data from the nucleus (SSU) and chloroplast elongation factor TU (tufA) sequences clearly revealed that the genus Ctenocladus, which has been classified in the Chaetophorales (Chlorophyceae) or Trebouxiophyceae incertae sedis by most phycologists, should be included in the Ulvales (Ulvophyceae) instead, and has a close relationship with the genera Pseudendoclonium and Phaeophila. We speculate that there may be undescribed or cryptic species especially in freshwater and other non-marine habitats. A phylogenetic re-evaluation based on large samples of microfilamentous ulvophycean algae especially freshwater specimens is needed.

Internal transcribed spacer 2 (nu ITS2 rRNA) sequence-structure phylogenetics: towards an automated reconstruction of the green algal tree of life.

BackgroundChloroplast-encoded genes (matK and rbcL) have been formally proposed for use in DNA barcoding efforts targeting embryophytes. Extending such a protocol to chlorophytan green algae, though, is fraught with problems including non homology (matK) and heterogeneity that prevents the creation of a universal PCR toolkit (rbcL). Some have advocated the use of the nuclear-encoded, internal transcribed spacer two (ITS2) as an alternative to the traditional chloroplast markers. However, the ITS2 is broadly perceived to be insufficiently conserved or to be confounded by introgression or biparental inheritance patterns, precluding its broad use in phylogenetic reconstruction or as a DNA barcode. A growing body of evidence has shown that simultaneous analysis of nucleotide data with secondary structure information can overcome at least some of the limitations of ITS2. The goal of this investigation was to assess the feasibility of an automated, sequence-structure approach for analysis of IT2 data from a large sampling of phylum Chlorophyta.Methodology/Principal FindingsSequences and secondary structures from 591 chlorophycean, 741 trebouxiophycean and 938 ulvophycean algae, all obtained from the ITS2 Database, were aligned using a sequence structure-specific scoring matrix. Phylogenetic relationships were reconstructed by Profile Neighbor-Joining coupled with a sequence structure-specific, general time reversible substitution model. Results from analyses of the ITS2 data were robust at multiple nodes and showed considerable congruence with results from published phylogenetic analyses.Conclusions/SignificanceOur observations on the power of automated, sequence-structure analyses of ITS2 to reconstruct phylum-level phylogenies of the green algae validate this approach to assessing diversity for large sets of chlorophytan taxa. Moreover, our results indicate that objections to the use of ITS2 for DNA barcoding should be weighed against the utility of an automated, data analysis approach with demonstrated power to reconstruct evolutionary patterns for highly divergent lineages.

Two new sacoglossan sea slug species (Opisthobranchia, Gastropoda): Ercolania annelyleorum sp. nov. (Limapontioidea) and Elysia asbecki sp. nov. (Plakobranchoidea), with notes on anatomy, histology and biology

Two new sacoglossan species, belonging to the genus Ercolania Trinchese, 1872 (Ercolania annelyleorum sp. nov.) and the genus Elysia Risso, 1818 (Elysia asbecki sp. nov.) are described from Lizard Island, Great Barrier Reef, Australia. Anatomy of both species was reconstructed by analyzing histological serial sections. Radula morphology was investigated by using light microscopy and scanning electron microscopy. Sequence analyses (NeighborNet; sequence divergence) and tree reconstructions showed for both species their distinction from con-generic species, but also two distinct mitochondrial lines in the new Ercolania species. Adults as well as freshly hatched juveniles of E. annelyleorum sp. nov. have been found in clusters of the ulvophycean alga Boodlea sp., which are sucked out by piercing the cell walls with their radular teeth. This new species differs from other, similar transparent, Ercolania species by its pattern of the green branches of the digestive gland and the presence of two distinct red patches, one in the anterior and the other in the posterior third of the dorsal body part. This coloration and furthermore the combination of following characters distinguishes the new species from all other described Ercolania species so far: rhinophores, elliptic in cross section, with one distinct branch of digestive gland running half way up; cerata not inflated; smooth cutting edge of sabot-shaped tooth; two-lobed prostate gland and presence of two allosperm receptacles with no re-opening of the receptaculum seminis to the outside. According to sequence divergence data of CO1, two mitochondrial lines seem to be present in the new species, which are clearly distinct from all other included Ercolania species. Elysia asbecki sp. nov. differs from other Elysia species by its whitish coloration with orange and dark brown dots and a distinct lighter spot in the neck region of the head. The rhinophores exhibit a black and yellow ribbon at the tip. The species has distinct reddish patches at the anterior base of the parapodia (at the conjunction with the head), one along the middle part of the parapodial edge on both sides and very distinct lateral patches at the end of the foot. CO1 sequences clearly distinguish this species from all closely related Elysia species. The food source of Elysia asbecki sp. nov. could not be verified yet. Measurements of photosynthetic activity within these two new species indicate that E. annelyleorum sp. nov. digests chloroplasts immediately after sequestration, whereas Elysia asbecki sp. nov. shows high maximum quantum yield values, similar to E. timida (Risso, 1818) and E. crispata (Mørch, 1863), both known as long term retention forms.

Erratum to: New insights into Lithocodium aggregatum Elliott 1956 and Bacinella irregularis Radoičić 1959 (Late Jurassic–Lower Cretaceous): two ulvophycean green algae (?Order Ulotrichales) with a heteromorphic life cycle (epilithic/euendolithic)

The Late Jurassic–Lower Cretaceous microorganisms incertae sedis Lithocodium aggregatum Elliott and Bacinella irregularis Radoicic are taxonomically studied based on material from the Lower Aptian of the western Maestrat Basin (Spain). This study is supplemented with detailed photographs from Elliot’s type-material. Given that the original description of Lithocodium aggregatum is ambiguous, a detail from the holotype is chosen as an epitype to serve as an interpretative type (article 9.7 ICBN). Lithocodium is re-interpreted as a filamentous-septate heterotrichale ulvophycean alga (?order Ulotrichales) exhibiting a heteromorphic life cycle consisting of two phases: an epilithic gametophytic and a euendolithic sporophytic (Gomontia stage). Bacinella irregularis is interpreted and redescribed as a purely euendolithic ulvophycean alga which bores into either Lithocodium aggregatum or the substrate below Lithocodium crusts. A small microendolith boring into Lithocodium crusts capable of cryptobiotically stretching within its filamentous network is tentatively assigned to the siphonal chlorophyte Ostreobium Bornet and Flahault. Another associated microfilamentous boring chlorophyte with characteristic long thin hairs (setae) is described as Phaeophila? sp. The euendolithic community comprises a variety of micro- and macroborings that affect the thalli of Lithocodium. Finally, the filaments of the outer zone of the Lithocodium crust are infested by calcimicrobes (cyanobacteria, ?fungi). The description made by Elliott in his original work of the “inner layer” of Lithocodium aggregatum as “confused” is explained here as a complex multitaxon chlorophyte-calcimicrobial assemblage overprinted by multiple bioerosion ichnofabrics.

Desmochloris mollenhaueri a new terrestrial ulvophycean alga from south-west African soils. (Molecular phylogeny and systematics of terrestrial Ulvophyceae I.)

Desmochloris mollenhaueri a new terrestrial ulvophycean alga from south-west African soils. (Molecular phylogeny and systematics of terrestrial Ulvophyceae I.)

Behavior of Flagella and Eyespot during Fertilization of Anisogametes in Caulerpa racemosa (Forsskal) J. Agardh var. laetevirens (Montagne) (Ulvophyceae, Chlorophyta) Revealed by Field Emission Scanning Electron Microscopy

Respective fates of male and female flagella and the eyespot during fertilization of ulvophycean alga Caulerpa racemosa (Forsskal) J. Agardh var. laetevirens (Montagne) were studied using field emission scanning electron microscopy (FE-SEM). FE-SEM allowed visualization of the eyespot of the biflagellate gamete. The female gamete has one eyespot on a posterior position of the cell body; the male gamete does not. The female gamete eyespot was oriented to the direction of the plane of the flagellar beat. The female gamete is larger than the male one and has the only eyespot. For those reasons, the author followed the fate of the flagella and eyespot during fertilization. When both gametes were mixed, the initial cytoplasmic contact and cell fusion between them usually took place at the anterior end slightly below the flagellar base. In most mating pairs, the female gamete fuses at the left side of the eyespot and male gamete at a cell surface that is perpendicular to the plane of the flagellar beat. As fusion proceeds, the gamete pair is transformed into a quadriflagellate planozygote in which two flagella each from the male and female gametes point in nearly the same direction. In particular, the no. 2 flagellum of the female gamete and one male flagellum were directed to the eyespot. These observations indicated that cell fusion at the particular area of the gamete is important for proper arrangement of the flagella and eyespot in the planozygote.

PHYLOGENY OF THE ULVOPHYCEAE (CHLOROPHYTA): CLADISTIC ANALYSIS OF NUCLEAR‐ENCODED rRNA SEQUENCE DATA1

ABSTRACTCladistic analysis of nuclear‐encoded rRNA sequence data provided us with the basis for some new hypotheses of relationships within the green algal class Ulvophyceae. The orders Ulotrichales and Ulvales are separated from the clade formed by the remaining orders of siphonous and siphonocladous Ulvophyceae (Caulerpales, Siphonocladales /Cladophorales [S/C] complex, and the Dasycladales), by the Chlorophyceae and Pleurastrophyceae. Our results suggest that the Ulvophyceae is not a monophyletic group. Examination of inter‐ and intra‐ordinal relationships within the siphonous and siphonocladous ulvophycean algae revealed that Cladophora, Chaetomorpha, Anadyomene, Microdictyon, Cladophoropsis and Dictyosphaeria form a clade. Thus the hypothesis, based on ultrastructural features, that the Siphonocladales and Cladophorales are closely related is supported. Also, the Caulerpales is a monophyletic group with two lineages; Caulerpa, Halimeda, and Udotea comprise one, and Bryopsis and Codium comprise the other. The Dasycladales (Cymopolia and Batophora) also forms a clade, but this clade is not inferred to be the sister group to the S/C complex as has been proposed. Instead, it is either the sister taxon to the Caulerpales or basal to the Caulerpales and S/C clade The Trentepohliales is also included at the base of the siphonous and siphonocladous ulvophycean clade. The Pleurastrophyceae, which, like the Ulvophyceae, posses a counter‐clockwise arrangement of flagellar basal bodies, are more closely related to the Chlorophyceae than to the Ulvophyceae based on rRNA sequences. Thus, the arrangement of basal bodies does not diagnose a monophyletic group. Previously reported hypotheses of phylogenetic relationships of ulvophycean algae were tested. In each case, additional evolutionary steps were required to obtain the proposed relationships. Relationships of ulvophycean algae to other classes of green algae are discussed.

LIGHT‐HARVESTING PIGMENT‐PROTEIN COMPLEXES OF THE ULVOPHYCEAE (CHLOROPHYTA):CHARACTERIZATION AND PHYLOGENETIC SIGNIFICANCE1

ABSTRACTPhotosystem II light‐harvesting complexes were isolated from a number of ulvophycean algae. Some of these light‐harvesting complexes displayed unusual features, most notably a high apparent molecular weight (ca. 58,000) when isolated by lithium doderyl sulfate polyarrylamide gel electrophoresis. Other ulvophycean light‐harvesting complexes had a low‐molecular weight (ca. 30,000). The distribution of the high‐molecular weight complex was limited to certain members of the Caulerpales and Blastophysa rhizopus (Siphanocladales). Within the Caulerpales, there were also spectral differences between the high‐molecular weight and low‐molecular weight light‐harvesting complex types. The differences in light‐harvesting complexes in the Ulvophyceae suggest that there are two lines of evolution in the Caulerpales and that Blastophysa may be an intermediate between the Siphon‐ocladales and the Caulerpales.