Christian Boedeker

Systematics of the marine microfilamentous green algae Uronema curvatum and Urospora microscopica (Chlorophyta)

The microfilamentous green alga Uronema curvatum is widely distributed along the western and eastern coasts of the north Atlantic Ocean where it typically grows on crustose red algae and on haptera of kelps in subtidal habitats. The placement of this marine species in a genus of freshwater Chlorophyceae had been questioned. Molecular phylogenetic analysis of nuclear-encoded small and large subunit rDNA sequences reveal that U. curvatum is closely related to the ulvophycean order Cladophorales, with which it shares a number of morphological features, including a siphonocladous level of organization and zoidangial development. The divergent phylogenetic position of U. curvatum, sister to the rest of the Cladophorales, along with a combination of distinctive morphological features, such as the absence of pyrenoids, the diminutive size of the unbranched filaments and the discoid holdfast, warrants the recognition of a separate genus, Okellya, within a new family of Cladophorales, Okellyaceae. The epiphytic Urospora microscopica from Norway, which has been allied with U. curvatum, is revealed as a member of the cladophoralean genus Chaetomorpha and is herein transferred to that genus as C. norvegica nom. nov.

MOLECULAR PHYLOGENY AND TAXONOMY OF THE AEGAGROPILA CLADE (CLADOPHORALES, ULVOPHYCEAE), INCLUDING THE DESCRIPTION OF AEGAGROPILOPSIS GEN. NOV. AND PSEUDOCLADOPHORA GEN. NOV.1

The Aegagropila clade represents a unique group of cladophoralean green algae occurring mainly in brackish and freshwater environments. The clade is sister to the species‐rich and primarily marine Cladophora and Siphonocladus lineages. Phylogenetic analyses of partial LSU and SSU nrDNA sequences reveal four main lineages within the Aegagropila clade, and allow a taxonomic reassessment. One lineage consists of two marine ‘Cladophora’ species, for which the new genus Pseudocladophora and the new family Pseudocladophoraceae are proposed. For the other lineages, the family name Pithophoraceae is reinstated. Within the Pithophoraceae, the earliest diverging lineage includes Wittrockiella and Cladophorella calcicola, occurring mainly in brackish and subaerial habitats. The two other lineages are restricted to freshwater. One of them shows a strong tendency for epizoism, and consists of Basicladia species and Arnoldiella conchophila. The other lineage includes Aegagropila, Pithophora and a small number of tropical ‘Cladophora’ species. The latter are transferred to the new genus Aegagropilopsis. Previously, polypyramidal pyrenoids had been suggested to be apomorphous for this clade, but we report the finding of both polypyramidal and bilenticular pyrenoids in members of the Pithophoraceae, and thus show that this character has no diagnostic value.

Cladophora rhodolithicola sp. nov. (Cladophorales, Chlorophyta), a diminutive species from European maerl beds

Cladophora rhodolithicola sp. nov., a small green macroalgal epiphyte on rhodoliths, is described from the Atlantic coasts of the British Isles, France and Spain, based on morphological and molecular evidence. Molecular phylogenetic analyses reveal that the rhodolith epiphyte is closely related to C. pygmaea, a dwarf species that also grows on maerl and small stones and whose systematic position was previously uncertain. The fact that both species, along with two other distinct Cladophora species (C. echinus and C. battersii), are resolved among species traditionally assigned to the Cladophora section Longi-articulatae, has implications for our understanding of the evolution of the genus. The section Longi-articulatae is one of the most distinctive groups in Cladophora, being characterized by coarse thalli with conspicuous basal cells, strict acropetal growth and the lack of intercalary rhizoids. Here we show that deviant character states such as reduced and irregular growth, and intercalary rhizoids have evolved independently several times within this clade.

Cladophoropsis brachyartra from southern South America is a synonym of Wittrockiella lyallii (Cladophorophyceae, Chlorophyta), previously regarded as endemic to New Zealand

Boedeker C., Ramírez M.E. and Nelson W.A. 2010. Cladophoropsis brachyartra from southern South America is a synonym of Wittrockiella lyalli (Cladophorophyceae, Chlorophyta), previously regarded as endemic to New Zealand. Phycologia 49: 525–536. DOI: 10.2216/09-98.1 Wittrockiella lyallii is a poorly known green macroalga that has been regarded as endemic to southern New Zealand. A herbarium specimen from southern Chile was discovered that conforms to the description of W. lyallii. Subsequently, it was realised that the South American species Cladophoropsis brachyartra is morphologically and ecologically equivalent to W. lyallii. Sequences of three ribosomal genes, including the internal transcribed spacer, from material collected in Chile and New Zealand are identical, suggesting recent long-distance dispersal from New Zealand to South America. The synonymisation of C. brachyartra with W. lyallii is presented here. Furthermore, the resulting disjunct distribution of the species is discussed in the light of sea surface temperatures, habitat availability in the Southern Ocean and winter sea ice extent during the last glacial maximum.

Global Decline of and Threats to Aegagropila linnaei, with Special Reference to the Lake Ball Habit

The freshwater macroalga Aegagropila linnaei can occur attached or unattached, but is best known for its free-floating spherical growth form (“lake balls,” “Cladophora balls,” or “marimo””). The worldwide distribution of this species was reconstructed using more than 1200 specimens from 28 herbaria, an extensive literature survey, and field observations. Aegagropila linnaei was found in 283 locations, with the majority located in central and northern Europe. Few records of A. linnaei exist from North America, but it is relatively widespread in Japan. The preferred habitat is inferred to be oligomesotrophic lakes with moderate to high calcium levels. In more than 50% of the known locations, A. linnaei has not been found in the last 30 years, and this decline is assumed to be correlated with changes in trophic conditions in those lakes. The unattached growth forms show a stronger decline than attached populations as a result of the habitat types in which they can occur.

Molecular phylogeny of the Cladophoraceae (Cladophorales, Ulvophyceae), with the resurrection of Acrocladus Nägeli and Willeella Børgesen, and the description of Lurbica gen. nov. and Pseudorhizoclonium gen. nov.

The taxonomy of the Cladophoraceae, a large family of filamentous green algae, has been problematic for a long time due to morphological simplicity, parallel evolution, phenotypic plasticity, and unknown distribution ranges. Partial large subunit (LSU) rDNA sequences were generated for 362 isolates, and the analyses of a concatenated dataset consisting of unique LSU and small subunit (SSU) rDNA sequences of 95 specimens greatly clarified the phylogeny of the Cladophoraceae. The phylogenetic reconstructions showed that the three currently accepted genera Chaetomorpha, Cladophora, and Rhizoclonium are polyphyletic. The backbone of the phylogeny is robust and the relationships of the main lineages were inferred with high support, only the phylogenetic position of both Chaetomorpha melagonium and Cladophora rupestris could not be inferred unambiguously. There have been at least three independent switches between branched and unbranched morphologies within the Cladophoraceae. Freshwater environments have been colonized twice independently, namely by the freshwater Cladophora species as well as by several lineages of the Rhizoclonium riparium clade. In an effort to establish monophyletic genera, the genera Acrocladus and Willeella are resurrected and two new genera are described: Pseudorhizoclonium and Lurbica.

Does the lack of mannitol accumulation in an isolate of Rhodella maculata (Rhodellophyceae, Rhodophyta) from the brackish Baltic Sea indicate a stressed population at the distribution limit?

The unicellular red alga Rhodella maculata Evans is reported for the first time from the central Baltic Sea (habitat salinity 5u2009psu). To evaluate whether this Baltic isolate is locally adapted to the brackish environment, its salt stress response was compared with a marine isolate (33u2009psu) by measuring growth rates, photosynthetic performance and the concentration of the osmolyte mannitol as a function of changing salinity between 1 and 60u2009psu. The brackish Baltic isolate grew between 5 and 40u2009psu, a narrower salinity range than in the marine isolate (1–60u2009psu). The marine isolate of R. maculata showed adaptations to an intertidal habitat with fluctuating salinities rather than to stable salinity conditions. The cells of the marine isolate performed a pronounced regulation of primary photosynthesis via non-photochemical quenching (NPQ), and accumulation of mannitol was involved in osmotic acclimation as intracellular concentrations increased considerably with rising salinities from 1 to 180u2009µmolu2009g−1u2009dry weight. At its habitat salinity (5u2009psu), the brackish isolate achieved only 39% of the growth rate measured at 33u2009psu; when exposed to higher salinities it lacked the ability to carry out substantial NPQ regulation, and it did not accumulate mannitol. However, when cultured at 33u2009psu for more than three months, the Baltic isolate showed a considerably improved salinity response in the higher salinity range (33–60u2009psu). Thus, the Baltic Sea isolate of R. maculata does not seem to be locally adapted to its brackish environment, and should be regarded as a stressed population at its distributional limit.

The Plastid Genome in Cladophorales Green Algae Is Encoded by Hairpin Chromosomes

Virtually all plastid (chloroplast) genomes are circular double-stranded DNA molecules, typically between 100 and 200 kb in size and encoding circa 80-250 genes. Exceptions to this universal plastid genome architecture are very few and include the dinoflagellates, where genes are located on DNA minicircles. Here we report on the highly deviant chloroplast genome of Cladophorales green algae, which is entirely fragmented into hairpin chromosomes. Short- and long-read high-throughput sequencing of DNA and RNA demonstrated that the chloroplast genes of Boodlea composita are encoded on 1- to 7-kb DNA contigs with an exceptionally high GC content, each containing a long inverted repeat with one or two protein-coding genes and conserved non-coding regions putatively involved in replication and/or expression. We propose that these contigs correspond to linear single-stranded DNA molecules that fold onto themselves to form hairpin chromosomes. The Boodlea chloroplast genes are highly divergent from their corresponding orthologs, and display an alternative genetic code. The origin of this highly deviant chloroplast genome most likely occurred before the emergence of the Cladophorales, and coincided with an elevated transfer of chloroplast genes toxa0the nucleus. A chloroplast genome that is composed only of linear DNA molecules is unprecedented among eukaryotes, and highlights unexpected variation in plastid genome architecture.

The occurrence of mycosporine-like amino acids in the gametophytic and sporophytic stages of Bangia (Bangiales, Rhodophyta)

C. Boedeker and U. Karsten. 2005. The occurrence of mycosporine-like amino acids in the gametophytic and sporophytic stages of Bangia (Bangiales, Rhodophyta). Phycologia 44: 403–408. Ultraviolet-absorbing mycosporine-like amino acids (MAAs) were identified and quantified in both the gametophytic and sporophytic life stages of the cosmopolitan intertidal genus Bangia. Field samples were compared with culture material originating from different biogeographic regions, including freshwater populations. All cultures were kept for a long time under low-irradiance conditions prior to MAA analysis. Within all isolates investigated, four distinct compounds were found which were identified as shinorine, porphyra-334, asterina-330 and palythine. Gametophytic filaments always exhibited high concentrations of MAAs, with porphyra-334 being the dominant compound. Field and culture material did not differ in the amount of MAAs, indicating that Bangia does not adjust the amount of sunscreens to environmental conditions. Freshwater isolates contained lower amounts of MAAs compared to marine strains. However, a biogeographical trend in MAA contents reflecting the origin of the samples from habitats with different climate and insolation was not observed. Even the shell-boring sporophytic conchocelis stage contained significant amounts of MAAs, but in lower concentrations than the gametophytes, raising the possibility of MAAs fulfiling different functions in the two life stages.

Molecular, biochemical and morphological data suggest an affiliation of Spongiochrysis hawaiiensis with the Trentepohliales (Ulvophyceae, Chlorophyta)

The aeroterrestrial, unicellular green alga Spongiochrysis hawaiiensis had been included in the ulvophycean order Cladophorales based on small subunit (SSU) rDNA sequence data, and represents so far the only fully terrestrial member of this order. Other characteristics of S.u2009hawaiiensis that are atypical for Cladophorales include the presence of large amounts of carotenoids and a budding‐like mode of cell division. As the position of this terrestrial, unicellular alga in an order of aquatic, multicellular green algae is unusual, we re‐evaluated the phylogenetic relationships of this enigmatic organism based on supplementary SSU rDNA sequences as well as novel large ribosomal subunit (LSU) rDNA and internal transcribed spacer (ITS rDNA) sequences. Additionally, we examined several morphological characters of S.u2009hawaiiensis, as well as low molecular weight carbohydrate (LMWC) patterns of S.u2009hawaiiensis and members of the Cladophorales and Trentepohliales as potential chemotaxonomic markers. We found S.u2009hawaiiensis to be uninucleate. The analysis of the LMWC content detected the presence of the polyol erythritol in S.u2009hawaiiensis and in the Trentepohliales, while this compound was missing in the Cladophorales. The phylogenetic analyses of the novel sequences placed S.u2009hawaiiensis in the terrestrial Trentepohliales. This placement is supported by the aeroterrestrial habitat, the presence of large amounts of carotenoids, the uninucleate cells, and the presence of the polyol erythritol as a protective compound against water loss.