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Issue Title: Phytoplankton and Equilibrium Concept: The Ecology of Steady-State Assemblages The cryptomonads sampled frequently from pelagial of large freshwater bodies, lakes and ponds, but also found in littoral regions and in small water bodies covered with vegetation, are often characterized by the sigmoid (S-shaped) form of their cells. According to the quoted findings of electron microscopy it seems that these species should be incorporated into the new genus Campylomonas Hill. Because the EM characteristics have not been proved so far for all species, and the following nomenclatural combinations accomplished, the traditional classification into the genus Cryptomonas is kept here. The correct name for the largest of sigmoid cryptomonads is Cryptomonas curvataEhr. em. Penard. Contrarily, C. rostrata Troitz. em. Kisel. is to be held for later synonyms. The existence of the species C. rostratiformis Skuja remains uncertain. The smaller species of sigmoid shape, i.e. C. reflexa (Marss.) Skuja and C. marssonii Skuja, may also easily be discerned under the light microscope. From the small puddles with H^sub 2^S in water, shortened forms of both these species are documented, one of them under the published name C. anas Javorn. The pelagic assemblage of the above sigmoid cryptomonads frequently is completed by Plagioselmis nannoplanctica (Skuja) Novar., Lucas et Morr. and by P. lacustris (Pasch. et Ruttn.) Javorn. These flagellates so far are currently determined as the species of the genus RhodomonasKarsten. In addition to the EM characteristic, they differ from Rhodomonas by the absence of a true gullet (pseudopharynx) having only the ventral furrow with rows of superficial ejectosomes (similar to the genus Cryptochrysis Pascher). The ellipsoidal or ovoid cryptomonads are sampled more frequently from peat pools and small water bodies covered with vegetation than from open pelagial of lakes. An erroneous determination of them causes confusion. Because some strains are wrongly labeled, electron-microscopic characteristics are vaguely determined species. For example, some EM features of Cryptomonas ovata in fact belong to C. pyrenoidifera Geitl. or to C. phaseolus Skuja. Cryptomonas ovata Ehr. em. Stein is not a collective species with a wide dimensional range of ellipsoid cells. It is a large species the typical morphology which is described here in detail. C. splendida Czosn. differs from C. ovata only by the transversal orientation of the cell. Similar to C. ovata but smaller species is C. tatrica Czosn. These species are further compared with the well-defined species C. obovata Skuja and the particularly small C. phaseolus Skuja.[PUBLICATION ABSTRACT]

Microalgae can stimulate antioxidant defense systems as adaptive responses to oxidative stress. Therefore, these organisms can be a potential source of natural antioxidants. In this work, forty-two strains of microalgae and cyanobacteria were selected within major groups held in the Coimbra Collection of Algae (ACOI). The antioxidant capacity of ethanolic extracts was determined by two spectrophotometric methods: the 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assay and the 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH) assay. Raspberry extract was used as a reference for comparison purposes. The ABTS assay showed an antioxidant capacity range of 16.61 ± 0.15 to 258.20 ± 0.65 mg Trolox (TE) (100 g) −1 fresh biomass (FW). High antioxidant capacity was observed in Eustigmatophyceae and Chlorophyta, with high results achieved for Vischeria helvetica ACOI 299, Characiopsis aquilonaris ACOI 2424, and Micrasterias radiosa var. elegantior ACOI 1568. The DPPH assay revealed that the eustigmatophytes Characiopsis sp. ACOI 2428, Characiopsis minima ACOI 2426, and V. helvetica ACOI 299, the cryptophyte Cryptomonas pyrenoidifera ACOI 1850, and the chlorophyte Mychonastes homosphaera ACOI 1850 had the highest scavenging activity. Cyanophytes revealed low antioxidant capacity, and mucilagineous strains of different taxa remained undetermined. The assessment of these strains and the broadening of a screening survey of the ACOI Culture Collection are expected to reveal very promising antioxidant-producing strains that may be applied in the field of human nutrition.

Abstract In many lineages of algae and land plants, photosynthesis was lost multiple times independently. Comparative analyses of photosynthetic and secondary nonphotosynthetic relatives have revealed the essential functions of plastids, beyond photosynthesis. However, evolutionary triggers and processes that drive the loss of photosynthesis remain unknown. Cryptophytes are microalgae with complex plastids derived from a red alga. They include several secondary nonphotosynthetic species with closely related photosynthetic taxa. In this study, we found that a cryptophyte, Cryptomonas borealis, is in a stage just prior to the loss of photosynthesis. Cryptomonas borealis was mixotrophic, possessed photosynthetic activity, and grew independent of light. The plastid genome of C. borealis had distinct features, including increases of group II introns with mobility, frequent genome rearrangements, incomplete loss of inverted repeats, and abundant small/medium/large-sized structural variants. These features provide insight into the evolutionary process leading to the loss of photosynthesis.

A new species, Cryptomonas tropica sp. nov., is described from Cat Tien National Park (Vietnam) based on morphological and molecular data. Strains of the new species were isolated from soil, which is an unusual environment for photosynthetic cryptomonads. This species has elliptical cells in ventral view and a single plastid notched into several irregular lobes without microscopically visible pyrenoids. Phylogenetic relationships inferred from nuclear-encoded SSU, LSU, ITS2 rDNA and psbA cpDNA show that the new species forms an independent branch on the phylogenetic tree of the genus Cryptomonas. In all phylogenetic analyses, this lineage was sister to clades containing other small-celled, pyrenoid-less species: Cryptomonas erosa, C. parmana, C. macilenta, C. obovoidea and C. commutata. C. tropica has been observed in two distant localities in Cat Tien National Park.

The effect of long-term changes in total precipitation on physical and chemical parameters of the water and the structure of phytoplankton community during a year were studied in a deep hard water lake. With respect to total precipitation, two different periods were distinguished: dry and wet. In the wet period, the water level rose and caused an increase in the water colour and a decrease in the electrolytic conductivity and concentration of nutrients. These changes were reflected in the composition and amount of phytoplankton. Certain phytoplankton groups, e.g. Cryptophyceae , Dinophyceae , Chrysophyceae , Bacillariophyceae and Chlorophyta/Charophyta , were positively affected by the environmental changes; instead, these effects were not observed in Cyanobacteria and Euglenophyta . The development of flagellates, such as Cryptomonas curvata , Plagioselmis nannoplanctica and Ceratium hirundinella , was enhanced during the wet period, whereas the dry period favoured non-flagellates, such as Planktothrix agardhii , Planktothrix rubescens and Limnothrix planctonica . Hence, the long-term variability in total precipitation can be a switch from non-flagellate- to flagellate-dominated phytoplankton in lakes. Moreover, a short time of ice cover duration in winter linked with the wet period promoted phytoplankton groups typical for spring and autumn, e.g. Cryptophyceae and Bacillariophyceae .

Terrestrial organic matter inputs have long been thought to play an important role in aquatic food web dynamics. Results from recent whole lake ¹³C addition experiments suggest terrestrial particulate organic carbon (t-POC) inputs account for a disproportionate portion of zooplankton production. For example, several studies concluded that although t-POC only represented [almost equal to]20% of the flux of particulate carbon available to herbivorous zooplankton, this food source accounted for [almost equal to]50% of the C incorporated by zooplankton. We tested the direct dietary impact of t-POC (from the leaves of riparian vegetation) and various phytoplankton on Daphnia magna somatic growth, reproduction, growth efficiency, and lipid composition. By itself, t-POC was a very poor quality resource compared to cryptophytes, diatoms, and chlorophytes, but t-POC had similar food quality compared to cyanobacteria. Small additions of high quality Cryptomonas ozolinii to t-POC-dominated diets greatly increased Daphnia growth and reproduction. When offered alone, t-POC resulted in a Daphnia growth efficiency of 5 ± 1%, whereas 100% Cryptomonas and Scenedesmus obliquus diets resulted in growth efficiencies of 46 ± 8% (± SD) and 36 ± 3%, respectively. When offered in a 50:50 mixed diet with Cryptomonas or Scenedesmus, the t-POC fraction resulted in a partial growth efficiency of 22 ± 9% and 15 ± 6%, respectively. Daphnia that obtained 80% of their available food from t-POC assimilated 84% of their fatty acids from the phytoplankton component of their diet. Overall, our results suggest Daphnia selectively allocate phytoplankton-derived POC and lipids to enhance somatic growth and reproduction, while t-POC makes a minor contribution to zooplankton production.

Filtration patterns in the fairy shrimp Eubranchipus grubii were analysed under laboratory conditions using water containing phytoplankton from their actual locality in western Poland. After 48 hours of feeding, we compared the structure of algal communities in water samples in treatments with males, females and control. The mean filtration rate for E. grubii was relatively high (14,488 mL h-1) in comparison to other crustacean filter feeders and was higher for females than for males. Fairy shrimps grazed effectively on all 11 dominant phytoplankton taxa and there was no sign of overall preferences with regard to taxon, cell volume, length or shape. Female fairy shrimps removed significantly more cells of three taxa (Cryptomonas erosa, C. ovata and Trachelomonas volvocina). The differences between sexes did not depend on the cell volume or length of particular phytoplankton taxa but were significantly related to their initial abundance, initial biomass and shape. The higher the abundance and biomass of the algal taxa, the more intensively it was grazed by females than by males. Females were also observed to graze more on spherical and elongated cells. In conclusion, our results show E. grubii to be an effective, generalist filter feeder capable of significantly influencing the phytoplankton community of a vernal pool. Possible implications of such grazing pressure are also discussed.

Genic DNA functions are commonplace: coding for proteins and specifying non-messenger RNA structure. Yet most DNA in the biosphere is non-genic, existing in nuclei as non-coding or secondary DNA. Why so much secondary DNA exists and why its amount per genome varies over orders of magnitude (correlating positively with cell volume) are central biological problems. A novel perspective on secondary DNA function comes from natural eukaryote-eukaryote chimaeras (cryptomonads and chlorarachneans) where two phylogenetically distinct nuclei have coevolved within one cell for hundreds of millions of years. By comparing cryptomonad species differing 13-fold in cell volume, we show that nuclear and nucleomorph genome sizes obey fundamentally different scaling laws. Following a more than 125-fold reduction in DNA content, nucleomorph genomes exhibit little variation in size. Furthermore, the present lack of significant amounts of nucleomorph secondary DNA confirms that selection can readily eliminate functionless nuclear DNA, refuting 'selfish' and 'junk' theories of secondary DNA. Cryptomonad nuclear DNA content varied 12-fold: as in other eukaryotes, larger cells have extra DNA, which is almost certainly secondary DNA positively selected for a volume-related function. The skeletal DNA theory explains why nuclear genome size increases with cell volume and, using new evidence on nucleomorph gene functions, why nucleomorph genomes do not.

There is considerable interest in the pathways by which carbon and growth-limiting elemental and biochemical nutrients are supplied to upper trophic levels. Fatty acids and sterols are among the most important molecules transferred across the plant-animal interface of food webs. In lake ecosystems, in addition to phytoplankton, bacteria and terrestrial organic matter are potential trophic resources for zooplankton, especially in those receiving high terrestrial organic matter inputs. We therefore tested carbon, nitrogen, and fatty acid assimilation by the crustacean Daphnia magna when consuming these resources. We fed Daphnia with monospecific diets of high-quality ( Cryptomonas marssonii ) and intermediate-quality ( Chlamydomonas sp. and Scenedesmus gracilis ) phytoplankton species, two heterotrophic bacterial strains, and particles from the globally dispersed riparian grass, Phragmites australis , representing terrestrial particulate organic carbon (t-POC). We also fed Daphnia with various mixed diets, and compared Daphnia fatty acid, carbon, and nitrogen assimilation across treatments. Our results suggest that bacteria were nutritionally inadequate diets because they lacked sterols and polyunsaturated omega-3 and omega-6 (ω-3 and ω-6) fatty acids (PUFAs). However, Daphnia were able to effectively use carbon and nitrogen from Actinobacteria, if their basal needs for essential fatty acids and sterols were met by phytoplankton. In contrast to bacteria, t-POC contained sterols and ω-6 and ω-3 fatty acids, but only at 22%, 1.4%, and 0.2% of phytoplankton levels, respectively, which indicated that t-POC food quality was especially restricted with regard to ω-3 PUFAs. Our results also showed higher assimilation of carbon than fatty acids from t-POC and bacteria into Daphnia, based on stable-isotope and fatty acids analysis, respectively. A relatively high (>20%) assimilation of carbon and fatty acids from t-POC was observed only when the proportion of t-POC was >60%, but due to low PUFA to carbon ratio, these conditions yielded poor Daphnia growth. Because of lower assimilation for carbon, nitrogen, and fatty acids from t-POC relative to diets of bacteria mixed with phytoplankton, we conclude that the microbial food web, supported by phytoplankton, and not direct t-POC consumption, may support zooplankton production. Our results suggest that terrestrial particulate organic carbon poorly supports upper trophic levels of the lakes.

Kleiber’s law describes the scaling of metabolic rate with body size across several orders of magnitude in size and across taxa and is widely regarded as a fundamental law in biology. The physiological origins of Kleiber’s law are still debated and generalizations of the law accounting for deviations from the scaling behavior have been proposed. Most theoretical and experimental studies of Kleiber’s law, however, have focused on the relationship between the average body size of a species and its mean metabolic rate, neglecting intraspecific variation of these 2 traits. Here, we propose a theoretical characterization of such variation and report on proof-of-concept experiments with freshwater phytoplankton supporting such framework. We performed joint measurements at the single-cell level of cell volume and nitrogen/carbon uptake rates, as proxies of metabolic rates, of 3 phytoplankton species using nanoscale secondary ion mass spectrometry (NanoSIMS) and stable isotope labeling. Common scaling features of the distribution of nutrient uptake rates and cell volume are found to hold across 3 orders of magnitude in cell size. Once individual measurements of cell volume and nutrient uptake rate within a species are appropriately rescaled by a function of the average cell volume within each species, we find that intraspecific distributions of cell volume and metabolic rates collapse onto a universal curve. Based on the experimental results, this work provides the building blocks for a generalized form of Kleiber’s law incorporating intraspecific, correlated variations of nutrient-uptake rates and body sizes.