| 1. |
- Ahlberg, Erik, et al.
(författare)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 2. |
- Johansson, Karin S L, et al.
(författare)
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Development of a quantitative PCR method to explore the historical occurrence of a nuisance microalga under expansion
- 2016
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Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883 .- 1878-1470. ; 56, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- A number of marine and freshwater harmful algal bloom (HAB) species have colonized new areas and expanded their habitat range in recent years. Nevertheless it is notoriously difficult to establish when colonization first occurred, what the dispersal routes are, and to separate recent invasion from increases in existent but small populations. The freshwater raphidophyte Gonyostomum semen is a nuisance species that has expanded its habitat range and increased in abundance in northern Europe during the past decades. To evaluate to what extent sediments can be used for determining historic occurrence of G. semen, a quantitative real-time PCR method for detecting cysts of this algae was developed. This paper presents a qPCR protocol with a set of primers that are specific to Gonyostomum and with PCR conditions optimized for sediment samples from humic lakes, which are the common habitat of G. semen. With this sensitive method as few as 1.6 cysts per PCR reaction could be reliably quantified, corresponding to 320 cysts per g wet weight sediment. Cysts were present in sediments with ages ranging from years to decades and their persistence allows detection of historic populations up to at least 50 years old. With this qPCR assay it will be possible to trace the presence of G. semen in environments prior to the onset of algae-specific monitoring programs as well as for quantification in water column samples. © 2016 The Authors.
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| 3. |
- Anderson, D M, et al.
(författare)
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Community assembly and seasonal succession of marine dinoflagellates in a temperate estuary: The importance of life cycle events
- 2006
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 51:2, s. 860-873
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Tidskriftsartikel (refereegranskat)abstract
- Dinoflagellate successional strategies and community structure were investigated in Perch Pond, a temperate estuary on the North American east coast by field surveys as well as laboratory investigations on growth rates, cyst maturation period, and cyst germination temperature thresholds. The dominant species were those predicted by the Smayda and Reynolds Rules of Assembly life form model. Three successional strategies were characterized: (1) holoplanktonic, (2) meroplanktonic (i.e., germinated from cysts), and (3) introduced by advection. The seasonal succession of the meroplanktonic dinoflagellates that were studied reflects the differential lengths of their mandatory dormancy periods as well as differences in their temperature thresholds or "windows" for germination. The holoplanktonic species present at low densities year-round in Perch Pond had a wide temperature tolerance for growth and thus did not need a cyst stage to survive seasonal extremes. Another non-cyst-forming species relied solely on advection to inoculate the salt pond; thus, blooms in successive years would be expected to be more stochastic in nature than for the other two strategies. The timing of cyst formation and population decline for meroplanktonic species corresponded on several occasions to an increase in grazers, suggesting that grazing might have contributed to bloom decline from cyst formation. This timing also suggests the possibility of encystment as a predator avoidance strategy. We suggest that seasonal succession of cyst-forming dinoflagellates is not stochastic. Instead, the appearance of these species in the plankton is predictable on the basis of measurable physiological responses to both endogenous and exogenous factors that they experience during dormancy and quiescence.
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| 4. |
- Andersson, Björn, 1985, et al.
(författare)
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Cross-contamination risks in sediment-based resurrection studies of phytoplankton
- 2022
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Ingår i: Limnology and Oceanography Letters. - : Wiley. - 2378-2242. ; 8:2, s. 376-84
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Tidskriftsartikel (refereegranskat)abstract
- Resurrection studies can answer some fundamental questions in aquatic ecology and evolutionary biology. For phytoplankton resting stages, longevity of thousands to millions of years has recently been reported. However, contamination during sediment sampling could distort these estimates, and this risk has not been systematically evaluated. Here we used 4.5 mu m diameter microspheres to quantify contamination while reviving the resting stages of seven abundant estuarine diatom and cyanobacterial taxa. We observed a sharp decline in resting stages abundance from 10(6) (g wet sediment)(-1) at the surface to < 0.8 (g wet sediment)(-1) at 12.5 cm depth. Added microspheres (similar to 4.5 x 10(7) cm(-2)) were translocated even deeper down the sediment and could well explain the vertical distributions and abundances of revived cells. Without this control, we could have claimed to have revived seven multi-decades to centennial-old taxa. Our findings suggest that improved contamination controls are needed for sediment core sampling of rare cells, microfossils, or DNA molecules.
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| 5. |
- Andersson, Björn, 1985, et al.
(författare)
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Differences in metal tolerance among strains, populations, and species of marine diatoms – Importance of exponential growth for quantification
- 2020
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Ingår i: Aquatic Toxicology. - : Elsevier BV. - 0166-445X .- 1879-1514. ; 226
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Tidskriftsartikel (refereegranskat)abstract
- © 2020 The Author(s) Strains of microalgae vary in traits between species and populations due to adaptation or stochastic processes. Traits of individual strains may also vary depending on the acclimatization state and external forces, such as abiotic stress. In this study we tested how metal tolerance differs among marine diatoms at three organizational levels: species, populations, and strains. At the species level we compared two pelagic Baltic Sea diatoms (Skeletonema marinoi and Thalassiosira baltica). We found that the between-species differences in tolerance (EC50) to the biologically active metals (Cu, Co, Ni, and Zn) was similar to that within-species. In contrast, the two species differed significantly in tolerance towards the non-essential metals, Ag (three-fold higher in T. baltica), Pb and Cd (two and three-fold higher in S. marinoi). At the population level, we found evidence that increased tolerance against Cu and Co (17 and 41 % higher EC50 on average, respectively) had evolved in a S. marinoi population subjected to historical mining activity. On a strain level we demonstrate how the growth phase of cultures (i.e., cellular densities above exponential growth) modulated dose-response relationships to Ag, Cd, Co, Cu, and Zn. Specifically, the EC50's were reduced by 10–60 % in non-exponentially growing S. marinoi (strain RO5AC), depending on metal. For the essential metals these differences were often larger than the average differences between the two species and populations. Consequently, without careful experimental design, interactions between nutrient limitation and metal stress may interfere with detection of small, but evolutionary and ecologically important, differences in tolerance between microalgae. To avoid such artifacts, we outline a semi-continuous cultivation approach that maintains, and empirically tests, that exponential growth is achieved. We argue that such an approach is essential to enable comparison of population or strain differences in tolerance using dose-response tests on cultures of microalgae.
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| 6. |
- Andersson, Björn, 1985, et al.
(författare)
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Intraspecific variation in metal tolerance modulate competition between two marine diatoms
- 2022
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Ingår i: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 16, s. 511-520
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Tidskriftsartikel (refereegranskat)abstract
- Despite widespread metal pollution of coastal ecosystems, little is known of its effect on marine phytoplankton. We designed a co-cultivation experiment to test if toxic dose–response relationships can be used to predict the competitive outcome of two species under metal stress. Specifically, we took into account intraspecific strain variation and selection. We used 72 h dose–response relationships to model how silver (Ag), cadmium (Cd), and copper (Cu) affect both intraspecific strain selection and competition between taxa in two marine diatoms (Skeletonema marinoi and Thalassiosira baltica). The models were validated against 10-day co-culture experiments, using four strains per species. In the control treatment, we could predict the outcome using strain-specific growth rates, suggesting low levels of competitive interactions between the species. Our models correctly predicted which species would gain a competitive advantage under toxic stress. However, the absolute inhibition levels were confounded by the development of chronic toxic stress, resulting in a higher long-term inhibition by Cd and Cu. We failed to detect species differences in average Cu tolerance, but the model accounting for strain selection accurately predicted a competitive advantage for T. baltica. Our findings demonstrate the importance of incorporating multiple strains when determining traits and when performing microbial competition experiments.
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| 7. |
- Andersson, Björn, et al.
(författare)
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Strain-specific metabarcoding reveals rapid evolution of copper tolerance in populations of the coastal diatom Skeletonema marinoi
- 2023
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Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X.
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Tidskriftsartikel (refereegranskat)abstract
- Phytoplankton have short generation times, flexible reproduction strategies, large population sizes and high standing genetic diversity, traits that should facilitate rapid evolution under directional selection. We quantified local adaptation of copper tolerance in a population of the diatom Skeletonema marinoi from a mining-exposed inlet in the Baltic Sea and in a non-exposed population 100 km away. We hypothesized that mining pollution has driven evolution of elevated copper tolerance in the impacted population of S. marinoi. Assays of 58 strains originating from sediment resting stages revealed no difference in the average tolerance to copper between the two populations. However, variation within populations was greater at the mining site, with three strains displaying hyper-tolerant phenotypes. In an artificial evolution experiment, we used a novel intraspecific metabarcoding locus to track selection and quantify fitness of all 58 strains during co-cultivation in one control and one toxic copper treatment. As expected, the hyper-tolerant strains enabled rapid evolution of copper tolerance in the mining-exposed population through selection on available strain diversity. Within 42 days, in each experimental replicate a single strain dominated (30%–99% abundance) but different strains dominated the different treatments. The reference population developed tolerance beyond expectations primarily due to slowly developing plastic response in one strain, suggesting that different modes of copper tolerance are present in the two populations. Our findings provide novel empirical evidence that standing genetic diversity of phytoplankton resting stage allows populations to evolve rapidly (20–50 generations) and flexibly on timescales relevant for seasonal bloom progressions.
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| 8. |
- Annenkova, Nataliia, et al.
(författare)
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Recent radiation in a marine and freshwater dinoflagellate species flock.
- 2015
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Ingår i: The Isme Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 9:8, s. 1821-1834
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Tidskriftsartikel (refereegranskat)abstract
- Processes of rapid radiation among unicellular eukaryotes are much less studied than among multicellular organisms. We have investigated a lineage of cold-water microeukaryotes (protists) that appear to have diverged recently. This lineage stands in stark contrast to known examples of phylogenetically closely related protists, in which genetic difference is typically larger than morphological differences. We found that the group not only consists of the marine-brackish dinoflagellate species Scrippsiella hangoei and the freshwater species Peridinium aciculiferum as discovered previously but also of a whole species flock. The additional species include Peridinium euryceps and Peridinium baicalense, which are restricted to a few lakes, in particular to the ancient Lake Baikal, Russia, and freshwater S. hangoei from Lake Baikal. These species are characterized by relatively large conspicuous morphological differences, which have given rise to the different species descriptions. However, our scanning electron microscopic studies indicate that they belong to a single genus according to traditional morphological characterization of dinoflagellates (thecal plate patterns). Moreover, we found that they have identical SSU (small subunit) rDNA fragments and distinct but very small differences in the DNA markers LSU (large subunit) rDNA, ITS2 (internal transcribed spacer 2) and COB (cytochrome b) gene, which are used to delineate dinoflagellates species. As some of the species co-occur, and all four have small but species-specific sequence differences, we suggest that these taxa are not a case of phenotypic plasticity but originated via recent adaptive radiation. We propose that this is the first clear example among free-living microeukaryotes of recent rapid diversification into several species followed by dispersion to environments with different ecological conditions.The ISME Journal advance online publication, 20 January 2015; doi:10.1038/ismej.2014.267.
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| 9. |
- Annenkova, Nataliia V., et al.
(författare)
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Closely related dinoflagellate species in vastly different habitats–an example of a marine–freshwater transition
- 2020
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Ingår i: European Journal of Phycology. - : Informa UK Limited. - 0967-0262 .- 1469-4433. ; 55:4, s. 478-489
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Tidskriftsartikel (refereegranskat)abstract
- Phytoplankton are present in a large variety of aquatic environments, ranging from small freshwater ponds to the oceans. Typically, freshwater and marine species are not closely related, indicating an ancient divergence and that salinity poses a strong dispersal barrier. Here we reveal a common recent origin of two dinoflagellates that are well adapted to different habitats. Gymnodinium baicalense inhabits the geologically old freshwater Lake Baikal, which is located in the middle of the Eurasian continent. Gymnodinium corollarium, on the other hand, is a brackish water species from the Baltic Sea. Both species form blooms under ice during the spring. We generated 10 DNA sequences from these species. The partial 28S rRNA gene from G. baicalense and the partial 18S rRNA gene and internal transcribed spacer-2 (ITS2) from G. corollarium were sequenced for the first time. A more detailed description of G. baicalense, which was previously known only from light microscopy observations, is also provided. In the laboratory we demonstrated that G. baicalense is strictly adapted to fresh water, while G. corollarium had a wide salinity tolerance. However, the two species have almost identical morphology, identical SSU rRNA gene sequences, and only small differences in the LSU rRNA gene and ITS2. We infer a common ancestor, which was a species from the Arctic region with a tolerance to a range of salinities. Our data support the scenario that the under-ice phytoplankton community in Lake Baikal has been formed recently, even though the lake is the oldest in the world.
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| 10. |
- Annenkova, Nataliia V., et al.
(författare)
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Delineating closely related dinoflagellate lineages using phylotranscriptomics
- 2018
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Ingår i: Journal of Phycology. - : Wiley. - 0022-3646. ; 54:4, s. 571-576
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Tidskriftsartikel (refereegranskat)abstract
- Recently radiated dinoflagellates Apocalathium aciculiferum (collected in Lake Erken, Sweden), Apocalathium malmogiense (Baltic Sea) and Apocalathium aff. malmogiense (Highway Lake, Antarctica) represent a lineage with an unresolved phylogeny. We determined their phylogenetic relationships using phylotranscriptomics based on 792 amino acid sequences. Our results showed that A. aciculiferum diverged from the other two closely related lineages, consistent with their different morphologies in cell size, relative cell length and presence of spines. We hypothesized that A. aff. malmogiense and A. malmogiense, which inhabit different hemispheres, are evolutionarily more closely related because they diverged from a marine common ancestor, adapting to a wide salinity range, while A. aciculiferum colonized a freshwater habitat, by acquiring adaptations to this environment, in particular, salinity intolerance. We show that phylotranscriptomics can resolve the phylogeny of recently diverged protists. This has broad relevance, given that many phytoplankton species are morphologically very similar, and single genes sometimes lack the information to determine species’ relationships.
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| 11. |
- Björnerås, Caroline, et al.
(författare)
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Inland blue holes of The Bahamas - chemistry and biology in a unique aquatic environment
- 2020
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Ingår i: Fundamental and Applied Limnology. - : Schweizerbart science publishers. - 1863-9135. ; 194:2, s. 95-106
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Tidskriftsartikel (refereegranskat)abstract
- While lake systems in temperate regions have been extensively studied, tropical and subtropical systems have received less attention. Here, we describe the water chemistry and biota of ten inland blue holes on Andros Island, The Bahamas, representative of the morphological, abiotic, and biotic variation among Androsian inland blue holes. The majority of the studied blue holes were vertically stratified with oxic freshwater overlying anoxic saline groundwater of marine origin. Water chemistry (e.g. total phosphorus and nitrogen) in shallow waters was similar among blue holes, while turbidity and water color varied. Presence of hydrogen sulfide and reduced iron in and below the halocline indicate reducing conditions in all stratified blue holes. The biota above the halocline was also similar among blue holes with a few taxa dominating the phytoplankton community, and the zooplankton community consisting of copepods and rotifers. The Bahamas mosquitofish (Gambusia hubbsi) was present in all investigated blue holes, often accompanied by other small planktivorous fish, while the piscivorous bigmouth sleeper (Gobiomorus donnitor) was only present in some of the blue holes. Our field study reinforces that inland blue holes are highly interesting for biogeochemical research, and provide naturally replicated systems for evolutionary studies.
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| 12. |
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| 13. |
- Brutemark, A, et al.
(författare)
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An experimental investigation of phytoplankton nutrient limitation in two contrasting low arctic lakes
- 2006
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Ingår i: Polar Biology. - : Springer Science and Business Media LLC. - 1432-2056 .- 0722-4060. ; 29:6, s. 487-494
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Tidskriftsartikel (refereegranskat)abstract
- We investigated whether phytoplankton communities in two lakes in SW Greenland were phosphorus or nitrogen limited. The study lakes have contrasting water chemistry (mean conductivities differ ten fold) and are located near Kangerlussuaq, SW Greenland (similar to 67 degrees N, 51 degrees W). A microcosm nutrient enrichment experiment was performed in June 2003 to determine whether nitrate or phosphate addition stimulated phytoplankton growth. Samples were analysed for species composition, biomass, and alkaline phosphatase activity (APA). Initially, both lakes had extremely low total phosphorus but high total nitrogen concentrations and high APA, suggesting that the phytoplankton were phosphorus limited prior to the start of the experiment. The phytoplankton composition and biomass (mainly Ochromonas spp.) responded to phosphate but not to nitrate addition. In both lakes, chlorophyll a increased significantly when phosphate was added. Furthermore, APA was significantly lower in the two lakes when phosphate was added compared to the control and the nitrogen addition treatment. The dominance of mixotrophic pbytoplankton and high DOC values suggest that these lakes may be regulated by microbial loop processes.
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| 14. |
- Bunse, Carina, et al.
(författare)
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Spatio-Temporal Interdependence of Bacteria and Phytoplankton during a Baltic Sea Spring Bloom
- 2016
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Ingår i: Frontiers in Microbiology. - : Frontiers Media S.A.. - 1664-302X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- In temperate systems, phytoplankton spring blooms deplete inorganic nutrients and are major sources of organic matter for the microbial loop. In response to phytoplankton exudates and environmental factors, heterotrophic microbial communities are highly dynamic and change their abundance and composition both on spatial and temporal scales. Yet, most of our understanding about these processes comes from laboratory model organism studies, mesocosm experiments or single temporal transects. Spatial -temporal studies examining interactions of phytoplankton blooms and bacterioplankton community composition and function, though being highly informative, are scarce. In this study, pelagic microbial community dynamics (bacteria and phytoplankton) and environmental variables were monitored during a spring bloom across the Baltic Proper (two cruises between North Germany to Gulf of Finland). To test to what extent bacterioplankton community composition relates to the spring bloom, we used next generation amplicon sequencing of the 16S rRNA gene, phytoplankton diversity analysis based on microscopy counts and population genotyping of the dominating diatom Skeletonema rnarinoi. Several phytoplankton bloom related and environmental variables were identified to influence bacterial community composition. Members of Bacteroidetes and Alphaproteobacteria dominated the bacterial community composition but the bacterial groups showed no apparent correlation with direct bloom related variables. The less abundant bacterial phyla Actinobacteria, Planctomycetes, and Verrucomicrobia, on the other hand, were strongly associated with phytoplankton biomass, diatom:dinoflagellate ratio, and colored dissolved organic matter (cDOM). Many bacterial operational taxonomic units (OTUs) showed high niche specificities. For example, particular Bacteroidetes OTUs were associated with two distinct genetic clusters of S. marinoi. Our study revealed the complexity of interactions of bacterial taxa with inter- and intraspecific genetic variation in phytoplankton. Overall, our findings imply that biotic and abiotic factors during spring bloom influence bacterial community dynamics in a hierarchical manner.
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| 15. |
- Bustamante-Gil, Carolina, et al.
(författare)
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Checklist, new records, and taxonomic annotations of freshwater thecate dinoflagellate (Dinophyceae) in Colombia
- 2021
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Ingår i: Phytotaxa. - : Magnolia Press. - 1179-3155 .- 1179-3163. ; 509:2, s. 135-167
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Tidskriftsartikel (refereegranskat)abstract
- A study on the freshwater dinoflagellate (Dinophyceae) of Colombia was carried out based on samples from four swamps, nine reservoirs, a small insular lake, and additional specimens deposited in the phycological collection of Universidad de Antioquia, Colombia, and the collection of Universidad de La Plata, Argentina. For most species, detailed morphological descriptions and illustrations are provided. Moreover, the geographical distribution of the species is updated. Durinskia spp., Glochidinium penardiforme, Naiadinium polonicum, Peridiniopsis elpatiewskyi, Peridiniopsis quadridens, and Sphaerodinium fimbriatum, are reported for the first time in Colombia. Furthermore, the correct sulcal plate pattern was determined for Naidinium polonicum which has been misinterpreted in earlier literature.
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| 16. |
- Carey, Cayelan C., et al.
(författare)
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The cyanobacterium Gloeotrichia echinulata stimulates the growth of other phytoplankton
- 2010
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 32:9, s. 1349-1354
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Tidskriftsartikel (refereegranskat)abstract
- We tested the effect of the cyanobacterium Gloeotrichia echinulata on a diverse array of phytoplankton. We found that Gloeotrichia increased the growth rates of five of seven phytoplankton species up to 620% in comparison with a medium-only control after 96 h.
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| 17. |
- Cornwallis, Charlie K, et al.
(författare)
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Single-cell adaptations shape evolutionary transitions to multicellularity in green algae
- 2023
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Ingår i: Nature Ecology and Evolution. - 2397-334X. ; 7:6, s. 889-902
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of multicellular life has played a pivotal role in shaping biological diversity. However, we know surprisingly little about the natural environmental conditions that favour the formation of multicellular groups. Here we experimentally examine how key environmental factors (predation, nitrogen and water turbulence) combine to influence multicellular group formation in 35 wild unicellular green algae strains (19 Chlorophyta species). All environmental factors induced the formation of multicellular groups (more than four cells), but there was no evidence this was adaptive, as multicellularity (% cells in groups) was not related to population growth rate under any condition. Instead, population growth was related to extracellular matrix (ECM) around single cells and palmelloid formation, a unicellular life-cycle stage where two to four cells are retained within a mother-cell wall after mitosis. ECM production increased with nitrogen levels resulting in more cells being in palmelloids and higher rates of multicellular group formation. Examining the distribution of 332 algae species across 478 lakes monitored over 55 years, showed that ECM and nitrogen availability also predicted patterns of obligate multicellularity in nature. Our results highlight that adaptations of unicellular organisms to cope with environmental challenges may be key to understanding evolutionary routes to multicellular life.
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| 18. |
- Figueroa, Rosa, et al.
(författare)
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From homothally to heterothally; mating preferences and genetic variation within clones of the dinoflagellate Gymnodinium catenatum
- 2010
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Ingår i: Deep-Sea Research. Part Ii, Topical Studies in Oceanography. - : Elsevier BV. - 0967-0645. ; 57:3-4, s. 190-198
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Tidskriftsartikel (refereegranskat)abstract
- The chain-forming dinoflagellate Gymnodinium catenatum Graham is responsible for outbreaks of paralytic shellfish poisoning (PSP), a human health threat in coastal waters. Sexuality in this species is of great importance in its bloom dynamics, and has been shown to be very complex but lacks an explanation. For this reason, we tested if unreported homothallic behavior and rapid genetic changes may clarify the sexual system of this alga. To achieve this objective, 12 clonal strains collected from the Spanish coast were analyzed for the presence of sexual reproduction. Mating affinity results, self-compatibility studies, and genetic fingerprinting (amplified fragment length polymorphism, AFLP) analysis on clonal strains, showed three facts not previously described for this species: (i) That there is a continuous mating system within G. catenatum, with either self-compatible strains (homothallic), or strains that needed to be outcrossed (heterothallic), and with a range of differences in cyst production among the crosses. (ii) There was intraclonal genetic variation, i.e. genetic variation within an asexual lineage. Moreover, the variability among homothallic clones was smaller than among the heterothallic ones. (iii) Sibling strains (the two strains established by the germination of one cyst) increased their intra- and inter-sexual compatibility with time. To summarize, we have found that G. catenatum's sexual system is much more complex than previously described, including complex homothallic/heterothallic behaviors. Additionally, high rates of genetic variability may arise in clonal strains, although explanations for the mechanisms responsible are still lacking. (C) 2009 Elsevier Ltd. All rights reserved.
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| 19. |
- Figueroa, R I, et al.
(författare)
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Effects of parental factors and meiosis on sexual offspring of Gymnodinium nolleri (Dinophyceae).
- 2006
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Ingår i: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 42:2, s. 350-362
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Tidskriftsartikel (refereegranskat)abstract
- Clonal strains of the dinoflagellate Gymnodinium nolleri Ellegaard and Moestrup were intercrossed to determine if cyst-related traits are genetically regulated and to clarify unknown aspects in the sexuality of this species. The objectives were to determine whether the parental identity influenced the physiological and morphological aspects of the cyst offspring, and to describe and compare nuclear development and cell division of encysting and non-encysting zygotes. Variables characteristic of each parental cross (difference in growth rates among parents, cyst production (CP), and genetic distance (GD) among parents assessed via an amplified fragment length analysis analysis) were studied to seek for possible relationships of the parental crosses with some characteristics of the cyst offspring (cyst size, length of dormancy period, germination success, and germling viability (V)). A principal component analysis using these variables showed three main results: (1) the dormancy period of cysts responded to a simple pattern of inheritance, (2) the larger the GD between parents, the smaller the CP, and progeny V, and (3) the size of cysts was influenced by both CP and the parental strain identity. A stable inheritance of the short dormancy period (14.6±5.5 days), dominant over medium (31.0±8.5 days) and long periods (52.7±9.2 days), was confirmed through two subsequent generations of cysts. The regulation of the sexual processes by a multiple loci system is discussed based on the pattern of inheritance of the dormancy period and the number of sexual recombination events recorded within cultures with self-CP capability. Fusion of the gamete nuclei happened 0–48 h after the total cytoplasmic fusion. The nucleus of the zygote was bilobed and had thick and distinct chromosomes. Similar processes of nuclear and cell division occurred in the non-encysting or encysting planozygote, and were characterized by the loss of the chromosomal structure, an apparent increase of the DNA content, and the formation of thinner chromosomes.
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| 20. |
- Figueroa, Rosa, et al.
(författare)
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Life cyle and sexuality of the freshwater raphidophyte Gonyostomum semen (Raphidophyceae)
- 2006
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Ingår i: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 42:4, s. 859-871
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Tidskriftsartikel (refereegranskat)abstract
- Previously unknown aspects in the life cycle of the freshwater flagellate Gonyostomum semen (Ehrenb.) (Raphidophyceae) are described here. This species forms intense blooms in many northern temperate lakes, and has increased in abundance and frequency in northern Europe during the past decades. The proposed life cycle is based on observations of life cycle stages and transitions in cultures. Viable stages of the life cycle were individually isolated and monitored by time-lapse photography. The most common processes undertaken by the isolated cells were: division, fusion followed by division, asexual cyst formation, and sexual cyst formation. Motile cells divided by two different processes. One lasted between 6 and 24 h and formed two cells with vegetative cell size and with or without the same shape. The second division process lasted between 10 and 20 min and formed two identical cells, half the size of the mother cell. Planozygotes formed by the fusion of hologametes subsequently underwent division into two cells. Asexual cyst-like stages were spherical, devoid of a thick wall and red spot, and germinated in 24-48 h. Heterogamete pairs were isogamous, and formed an angle of 0-90 degrees between each other. Planozygote and sexual cyst formation were identified within strains established from one vegetative cell. The identity of these strains, which was studied by an amplified fragment length polymorphism analysis, was correlated with the viability of the planozygote. Resting cyst germination was described using cysts collected in the field. The size and morphology of these cysts were comparable with those formed sexually in culture. The excystment rate was higher at 24 degrees C than at 19 or 16 degrees C, although the cell liberated during germination (germling) was only viable at 16 degrees C. The placement of G. semen within the Raphidophyceae family was confirmed by sequence analysis of a segment of the 18S ribosomal DNA.
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| 21. |
- Fistarol, Giovana, et al.
(författare)
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Temporary cyst formation in phytoplankton: a response to allelopathic competitors?
- 2004
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 6:8, s. 791-798
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Tidskriftsartikel (refereegranskat)abstract
- Competition among phytoplankton for limiting resources may involve direct or indirect interactions. A direct interaction of competitors is the release of chemicals that inhibit other species, a process known as allelopathy. Here, we investigated the allelopathic effect of three toxic microalgae species (Alexandrium tamarense, Karenia mikimotoi and Chrysochromulina polylepis) on a natural population of the dinoflagellate Scrippsiella trochoidea. Our major findings were that in addition to causing death of S. trochoidea cells, the allelopathic species also induced the formation of temporary cysts in S. trochoidea. Because cysts were not lysed, encystment may act as a defence mechanism for S. trochoidea to resist allelochemicals, especially when the allelopathic effect is moderate. By forming temporary cysts, S. trochoidea may be able to overcome the effect of allelochemicals, and thereby have an adaptive advantage over other organisms unable to do so.
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| 22. |
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| 23. |
- Godhe, Anna, 1967, et al.
(författare)
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Physical barriers and environmental gradients cause spatial and temporal genetic differentiation of an extensive algal bloom
- 2016
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Ingår i: Journal of Biogeography. - : John Wiley & Sons. - 0305-0270 .- 1365-2699. ; 43:6, s. 1130-1142
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Tidskriftsartikel (refereegranskat)abstract
- Aim: To test if a phytoplankton bloom is panmictic, or whether geographical and environmental factors cause spatial and temporal genetic structure.Location: Baltic Sea.Method: During four cruises, we isolated clonal strains of the diatom Skeletonema marinoifrom 9 to 10 stations along a 1132 km transect and analysed the genetic structure using eight microsatellites. Using F-statistics and Bayesian clustering analysis we determined if samples were significantly differentiated. A seascape approach was applied to examine correlations between gene flow and oceanographic connectivity, and combined partial Mantel test and RDA based variation partitioning to investigate associations with environmental gradients.Results: The bloom was initiated during the second half of March in the southern and the northern- parts of the transect, and later propagated offshore. By mid-April the bloom declined in the south, whereas high phytoplankton biomass was recorded northward. We found two significantly differentiated populations along the transect. Genotypes were significantly isolated by distance and by the south–north salinity gradient, which illustrated that the effects of distance and environment were confounded. The gene flow among the sampled stations was significantly correlated with oceanographic connectivity. The depletion of silica during the progression of the bloom was related to a temporal population genetic shift.Main conclusions: A phytoplankton bloom may propagate as a continuous cascade and yet be genetically structured over both spatial and temporal scales. The Baltic Sea spring bloom displayed strong spatial structure driven by oceanographic connectivity and geographical distance, which was enhanced by the pronounced salinity gradient. Temporal transition of conditions important for growth may induce genetic shifts and different phenotypic strategies, which serve to maintain the bloom over longer periods.
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| 24. |
- Gollnisch, Raphael, et al.
(författare)
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Calcium and pH interaction limits bloom formation and expansion of a nuisance microalga
- 2021
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590.
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Tidskriftsartikel (refereegranskat)abstract
- Microalgal range expansions are increasing in frequency and magnitude but generally remain unnoticed until mass development occurs. Gonyostomum semen is a freshwater raphidophyte that causes nuisance blooms in lakes and has recently expanded its distribution across Europe. G. semen was considered to mainly occur in humic lakes in the boreal region but is now found in high density also in other freshwater habitats on a larger geographic scale with growing incidence. In this study, we focused on which environmental factors limit its expansion. Our hypothesis was that G. semen occurs in many different lake types, except for high alkalinity lakes, in which high pH in combination with high calcium concentration would inhibit its growth. Results from our field study illustrate the environmental heterogeneity of G. semen bloom sites across Europe and the United States. Nevertheless, none of these sites combined high pH and high calcium concentration. In a mesocosm study, as well as a laboratory experiment, we further demonstrated that growth of G. semen is inhibited in conditions combining both high pH and high calcium concentration. We also discuss the function of Sphagnum peat mosses in rendering an alkaline habitat suitable to G. semen growth. Our study highlights that high alkalinity environments act as a major colonization barrier to G. semen. While this finding explains which environmental filters limit G. semen distribution it also helps in understanding its current expansion. With globally decreasing calcium concentrations in freshwater ecosystems, new habitats have and will become conducive to G. semen growth.
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| 25. |
- Gollnisch, Raphael, et al.
(författare)
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Sag-rad : A Method for Single-Cell Population Genomics of Unicellular Eukaryotes
- 2023
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Ingår i: Molecular biology and evolution. - 0737-4038. ; 40:5
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Tidskriftsartikel (refereegranskat)abstract
- Sequencing of reduced representation libraries enables genotyping of many individuals for population genomic studies. However, high amounts of DNA are required, and the method cannot be applied directly on single cells, preventing its use on most microbes. We developed and implemented the analysis of single amplified genomes followed by restriction-site-associated DNA sequencing to bypass labor-intensive culturing and to avoid culturing bias in population genomic studies of unicellular eukaryotes. This method thus opens the way for addressing important questions about the genetic diversity, gene flow, adaptation, dispersal, and biogeography of hitherto unexplored species.
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