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36 results for “Freshwater plankton”
Effects of freshwater salinization on a salt-naïve planktonic eukaryote community
Salinization of freshwater ecosystems is a widespread issue, but evidence of ecological effects on aquatic eukaryote communities remains scarce. We experimentally exposed naive planktonic communities of a north-temperate, freshwater lake to a gradient of chloride (Cl-) concentration (0.27-1400 mg Cl-.L-1) with in-situ mesocosms. Following six weeks of exposure, we measured changes in the diversity, composition, and abundance of eukaryotic 18S rRNA gene. Total phytoplankton biomass remained unchanged, but we observed a shift in dominant phytoplankton groups with elevated salt concentration, from Cryptophyta and Chlorophyta that dominated in lower chloride concentrations (<185 mg Cl-.L-1) to Ochrophyta that dominated at higher conductivity (>185 mg Cl-.L-1). Most zooplankton and rotifer taxa were sensitive to the salinity and disappeared at low chloride concentrations (<40 mg Cl-.L-1). While ciliates thrived at low chloride concentrations (<185 mg Cl-.L-1), fungal groups dominated at intermediate chloride concentrations (185 mg Cl-.L-1 to 640 mg Cl-.L-1), and only phytoplankton remained at the highest chloride concentrations (> 640 mg Cl-.L-1).
Fig. 12 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 12. Neoformation organelles in dividers of Limnostrombidium viride in the transmission electron microscope. (A) Oblique section of the organelle's distal (asterisk) and proximal portions with the outgrowing cilia of the oral primordium. The axonemes (arrowheads) are very short, lack the central pair of microtubules, and are bulbous because being embedded in many vesicles. (B) Cross section of cilia. Their axonemes already possess the "9×2+2" ultrastructure (arrowheads). (C) Tangential section of the neoformation organelle showing cross sections of cilia (arrowheads) and vesicles with electron-dense content of unknown function. (D) Longitudinal section of the posterior cell portion. Both the unciliated (arrowhead) and ciliated (double arrowhead) portions of the organelle are shown twice in cross section. MB, cell membrane; PE, perilemma; V, vesicles. Scale bars: 1 µm (A–C), 5 µm (D).
Fig. 11 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 11. Ring-canal of Limnostrombidium viride in the transmission electron microscope. The transverse section of the organelle shows its position between the anterior furrow (asterisk) and the stripe of extrusome attachment sites (arrow denotes the electron-dense cap of an empty "extrusome chamber"). Vesicles are adjacent to the irregular anterior membrane portion of the canal, while the posterior portion is underlain by two layers of perpendicularly orientated microtubules. ML, two layers of microtubules; PE, perilemma; RC, lumen of ringcanal; V, vesicles of unknown function. Scale bar: 1 µm.
Fig. 10 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 10. Extrusome attachment sites (A) and immature extrusomes (B, C) of L. viride in the TEM. (A) Freeze-fracture replica showing the extrusome attachment rosettes. (B, C) Transverse and longitudinal sections; white lines mark corresponding section planes. The extrusome shows in longitudinal section an electron-dense fusiform wall and an electron-light lumen with indistinct transverse stripes. The apical portion of the extrusome is surrounded by an electron-dense structure; both are enclosed by a membrane (arrowheads). The transverse section shows the extrusome to be composed of six electron-dense trapeziums arranged around a bright lumen. 1, attachment rosette with one central and eight peripheral particles; 2, first ring; 3, second ring; ED, electron-dense structure; EX, extrusomes. Scale bars: 1 µm.
Fig. 3 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 3. Oral ciliature of Limnostrombidium viride in the scanning (A) and transmission electron microscopes (B–D). (A) Proximal portion of the adoral zone of membranelles. The endoral membrane is usually covered by a cytoplasmic fold and a membranous sheet (probably perilemma). (B) Longitudinal section of the buccal lip and endoral membrane in ventral view. Note the numerous vesicles with fluffy content of unknown nature in the anterior cell half and especially in the buccal lip. The perilemma forms stacks in the buccal cavity, while it otherwise covers the cell only with a single layer. (C) Longitudinal section of the buccal vertex near the cytostome. The distal ends of the endoral cilia have modified axonemes (arrowhead), i.e., they have a reduced number of peripheral microtubular doublets. Some cilia of the buccal membranelles and the multiple membranes are also recognisable. (D) Transverse section of the basal bodies of the endoral membrane (seen from inside the buccal cavity). BL, buccal lip; BM, buccal membranelles; CM, collar membranelles; E, endoral membrane; ED, electron-dense bodies; LM, bifurcated left microtubular ribbons; NE, possibly nematodesmata; PE, perilemma; RM, right microtubular ribbons. Scale bars: 10 µm (A), 1 µm (B–D).
Fig. 9 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 9. Extrusomes of Limnostrombidium viride in the SEM (A, B) and TEM (C, D). (A) Lateral view of a cell. Arrowheads mark just ejected extrusomes. (B) Extrusome cluster. (C) Cross section of extrusome stripe. (D) Longitudinal section. One extrusome is just ejected (arrow), four are in the resting state, and three "empty chambers" (asterisks) are the remains of previously ejected extrusomes. CSL, concentric sheet layers; CT, curved tubules; EC, extrusome cores; ED, electron-dense bodies; EM, extrusome membranes; EX, extrusomes; GK, girdle kinety; MT, separating microtubules; PE, perilemma. Scale bars: 20 µm (A), 1 µm (B–D).
Fig. 7 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 7. Hemitheca of Limnostrombidium viride in the transmission electron microscope. (A) Tangential section showing the seams (arrow) between the polygonal cortical platelets, which are covered by the layer of longitudinal microtubules. (B) Freeze-fracture replica showing the seams between the polygonal platelets, the layer of longitudinally orientated microtubules, the alveoli, and remnants of the cell membrane with its densely arranged particles (arrows). (C) Transverse section showing the perilemma with its electron-dense bodies, the alveoli, the layer of longitudinal microtubules, and the polygonal cortical platelets. The arrowhead marks the cell membrane. AL, alveoli; CP, cortical platelets; MT, cortical microtubular layer; PE, perilemma. Scale bars: 1 µm.
Fig. 2 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 2. Transmission electron micrographs of collar membranelles in Limnostrombidium viride. Their anterior ends are directed to the left. (A–C) Transverse sections at different planes showing the various connections between the basal bodies of an individual membranelle and the microtubules extending into the cytoplasm. (D) The axonemes of the individual cilia are enclosed by the cell membrane, while all cilia of a membranelle are additionally surrounded by the perilemma. (E) Transverse sections of two polykinetids at the level of the basal bodies. The last file of the upper adoral membrane has associated short ciliary stubs only (arrowhead). 1–3, rows 1–3; ED, electron-dense bodies; IMF, intermembranellar fibre; M1, microtubular ribbons at row 1; M3, microtubular ribbons at row 3; PE, perilemma. Scale bars: 1 µm (A–C), 0.5 µm (D, E).
Fig. 6 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 6. Ventral kinety of Limnostrombidium viride in the transmission electron microscope. (A) Longitudinal section of a dikinetid showing the diverging basal bodies. A perilemma covers the cell surface. (B) Transverse section showing a dikinetid in the longitudinal furrow later- ally bordered by the cortical platelets of the hemitheca. CP, cortical platelets; ED, electron-dense bodies; ML, cortical microtubular layer; PE, perilemma; SC1, anterior dikinetidal cilium; SC2, posterior dikinetidal cilium. Scale bars: 1 µm.
Fig. 1 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 1. Limnostrombidium viride (A, schematic line drawing combining data from scanning and transmission electron microscopy; B, C, scanning electron micrographs). (A) General morphology. Note that the polygonal platelets of the hemitheca are only depicted in the cell periphery to show the more centrally located organelles. For the sake of clarity, the course of the neoformation organelle is somewhat stretched. (B, C) Ventral view and detail of ventral side. The arrowhead (C) marks the opening of the neoformation organelle in the stripe of extrusome attachment sites. BL, buccal lip; BM, buccal membranelles; CM, collar membranelles; EX, stripe of extrusome attachment sites; GK, girdle kinety; HT, hemitheca; MA, macronucleus; MI, micronucleus; NF, neoformation organelle; VK, ventral kinety. Scale bars: 30 µm (A), 20 µm (B), 10 µm (C).
Fig. 8 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 8. Nuclear apparatus of Limnostrombidium viride in the transmission electron microscope. (A) Interphase state showing the micronucleus in an indentation of the macronucleus, which has an irregular surface and contains numerous electron-dense inclusions, probably nucleoli. (B) A macronucleus showing the replication band. The arrow indicates the migration direction of the replication band. 1, zone of typical macronuclear structure; 2, zone characterised by protein and RNA production; 3, bright zone with beginning biosynthesis and DNA replication; MA, macronucleus; MI, micronucleus. Scale bars: 2 µm.
Fig. 4 in Some Ultrastructural Features of the Planktonic Freshwater Ciliate Limnostrombidium viride (Alveolata, Ciliophora, Oligotrichida) and Improved Diagnoses of Oligotrich Taxa
Fig. 4. Girdle kinety of Limnostrombidium viride (A, scanning electron micrograph; B, scheme of dikinetid). (A) Detail of kinety showing the two alternating types of girdle cilia. (B) Dikinetid with the associated structures; the presence of a transverse ribbon is uncertain. Numbering of the triplets (1–9) follows the "Grain convention", but is somewhat uncertain, as the triplets are difficult to identify. The scheme bases on numerous transmission electron micrographs (not shown). DS, desmose; KD, kinetodesmal fibril; PC, postciliary microtubular ribbon; SC1, club-shaped cilia of left dikinetidal basal bodies (originally anterior ones); SC2, condylocilia of right dikinetidal basal bodies (originally posterior ones). Scale bar: 2 µm.
Figures 1–4 in The freshwater medusa Limnocnida and associated plankton in the floodplain of the Ayeyarwaddy River, Myanmar
Figures 1–4. Limnocnida from Myanmar. (1) Whole umbrella showing primary tentacles on one quadrant, and all tentacles on another quadrant. (2) Umbrella margin, showing bases of two primary tentacles with associated secondary tentacles and statocysts. (3) Part of the basal region of a tentacle showing groups of nematocysts. (4) Arrangement of nematocysts near the tip of a tentacle.
Prickly postglacial pioneers: freshwater plankton community composition influences fatty acid desaturase (FADS2) copy number in Southern Greenland threespine sticklebacks
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Prey naiveté alters the balance of consumptive and non-consumptive predator effects and shapes trophic cascades in freshwater plankton
<p><span>Predators drive trophic cascades by reducing prey biomass and altering prey traits, selecting for prey that exhibit constitutive and induced anti-predator defenses that decrease susceptibility to consumption. These defense traits are often costly, generating a tradeoff between consumptive (CEs) and non-consumptive predator effects (NCEs). The ecological and evolutionary experience that prey share with a given predator may determine their position along this tradeoff curve, affecting the nature and strength of top-down control of ecosystems. Conceptual models predict that predator-experienced prey suffer greater NCEs than predator-naive prey, which suffer stronger CEs and total predator effects (CEs + NCEs), but this has not been tested in diverse prey communities. We tested these predictions by comparing the effects of predation (CEs + NCEs) and predation risk (NCEs only) of planktivorous fish on food web structure in pond mesocosms with diverse natural communities of either predator-naive or predator-experienced zooplankton. Contrary to expectations, top-down control of zooplankton and phytoplankton biomass was strengthened by prey community experience: in systems with experienced relative to naive zooplankton communities both predation risk (NCEs only) and predation (CEs + NCEs) had stronger effects on zooplankton prey biomass and trophic cascades were twice as strong. These results show that the ecological and evolutionary experience of diverse prey communities alters the balance of consumptive and non-consumptive predator effects and influences trophic cascade strength.</span></p>
Marine and freshwater planktonic ciliates differ in their thermal performance
<p><span>Predicting the performance of aquatic organisms in a future warmer climate depends critically on understanding how current temperature regimes affect the organisms' growth rates. Using a meta-analysis for published experimental data, we calculated the activation energy (E<sub>a</sub>) to parameterize the thermal sensitivity of marine and freshwater ciliates, major players in marine and freshwater food webs. We hypothesized that their growth rates increase with temperature but that ciliates dwelling in the immense, thermally stable ocean are closely adapted to their ambient temperature and have lower E<sub>a</sub> than ciliates living in smaller, thermally more variable freshwater environments. The E<sub>a</sub> was in the range known from other taxa but significantly lower for marine ciliates (</span><span>0.390 ± 0.105 eV) than for freshwater ciliates (0.633 ± 0.060 eV), supporting our hypothesis. Accordingly, models aiming to predict the ciliate response to increasing water temperature should apply the environment-specific activation energies provided in this study. </span></p>
Data from: Salty Sensors, Fresh Ideas: The use of molecular and imaging sensors in understanding plankton dynamics across marine and freshwater ecosystems
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Marine and freshwater planktonic ciliates differ in their thermal performance
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Prey naiveté alters the balance of consumptive and non-consumptive predator effects and shapes trophic cascades in freshwater plankton
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Dataset for: Cascading effects of freshwater salinization on plankton communities in the Sierra Nevada
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Allen Brain Atlas
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International Brain Laboratory public data
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OpenNeuro
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