| 1. |
- Godhe, Anna, 1967, et al.
(författare)
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Genetic and Microscopic Evidence for Sexual Reproduction in the Centric Diatom Skeletonema marinoi
- 2014
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Ingår i: Protist. - : Elsevier BV. - 1434-4610 .- 1618-0941. ; 165:4, s. 401-416
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Tidskriftsartikel (refereegranskat)abstract
- This study provides microscopic and molecular evidence for sexual reproduction in the homothallic centric diatom Skeletonema marinoi isolated from the Baltic Sea. The species is capable of restoring cell size asexually through an auxospore-like stage. However, cells were sexualized after shifting strains from low (6 PSU) to high (16 PSU) salinity. We observed flagellate male gametes and oogonia, with diameters of 3-4 and 3.2-6.3 m, respectively. Fertilization took place followed by the formation of round auxospores surrounded by thin siliceous incunabular scales. Auxosporulation was synchronized, and a maximum of auxospores was detected on day three following the salinity shift. The proportion of auxospores to vegetative cells ranged from 0.02 to 0.18. There was a significant correlation between auxosporulation success and inoculum cell density. At lower cell concentration (5,000 cells ml-1), pro- portionally fewer auxospores were formed. Auxospores were formed in single strains and in crosses of strains. The proportion of auxospores differed significantly among strains and crosses of strains. Additionally, we isolated single auxospores, obtained F1 strains and performed microsatellite based pedigree analysis of parental generations and their offspring. We proved that the auxospores were formed sexually, either by inter- or by intra-strain fertilization.
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| 2. |
- Klais, Riina, et al.
(författare)
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Spring phytoplankton communities shaped by interannual weather variability and dispersal limitation : Mechanisms of climate change effects on key coastal primary producers
- 2013
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 58:2, s. 753-762
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Tidskriftsartikel (refereegranskat)abstract
- Spring bloom composition in the Baltic Sea, a partially ice-covered brackish coastal waterbody, is shaped by winter-spring weather conditions affecting the relative dominance of diatoms and a heterogeneous assemblage of cold-water dinoflagellates, dominated by the chain-forming Peridiniella catenata and a complex of at least three medium-sized, single-celled species: Biecheleria baltica, Gymnodinium corollarium, and Scrippsiella hangoei. During the last decades, the bloom community has dramatically changed in several basins. We analyze here a 30 yr time series of quantitative phytoplankton data, as predicted by hindcast modeled ice thickness and storminess for three distinct Baltic Sea localities, to verify climate-driven mechanisms affecting the spring bloom composition. Thick (> 30 cm) and long-lasting ice cover favored diatom-dominated spring blooms, and mild winters, with storms and thin ice cover (10 to 20 cm), supported blooms of the B. baltica complex. Dispersal limitation plays an important role in the spatial extent of blooms of the B. baltica complex, caused by intricate interplay of local hydrodynamics and the dinoflagellate life cycle. Proportion peaks of key phytoplankton groups have shifted about 10 d earlier in the northwestern Baltic Sea (P. catenata and diatoms) and in the Gulf of Riga (P. catenata). The significant weather effects imply future shifts in spring bloom composition and consequent biogeochemical cycles, driven by the predicted changes in winter storminess and decrease in ice cover extent and duration in climate change models.
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| 3. |
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| 4. |
- Sundström, Annica M., et al.
(författare)
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Detection of the bloom-forming cold-water dinoflagellate Biecheleria baltica in the Baltic Sea using LSU rRNA probes
- 2010
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 61:2, s. 129-140
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Tidskriftsartikel (refereegranskat)abstract
- Cold-water dinoflagellates frequently dominate the spring phytoplankton community of the northern Baltic Sea and contribute substantially to the spring primary production. These dinoflagellate communities are largely composed of 3 different species (Biecheleria baltica, Scrippsiella hangoei, Gymnodinium corollarium) that cannot be unambiguously separated by conventional light microscopy. In this study, a fluorescence in situ hybridization (FISH) assay was developed for the detection of B. baltica in field samples. The probe-based method was tested and optimized in vitro, and potential effects of the B. baltica life-cycle transitions were evaluated by examining the labeling quality of the probes on different life-cycle stages before the assay was applied in a field study. The BbRNA4 probe had the highest specificity and was chosen for downstream applications. The life-cycle experiment showed significant differences in labeling efficiency between cultured cells from different growth phases, particularly for the nutrient-limited treatment compared to the control. Tests with spiked field samples revealed that cell recovery in the FISH assay was low (30%), resulting in a considerable underestimation of in situ abundances. However, a strong relationship between FISH and Utermohl counts of field samples suggests that trends of the bloom dynamics can be followed reliably by this method. By applying the FISH detection method in a field survey, we found that the dynamics of the B. baltica bloom follows that established earlier for the Scrippsiella/Biecheleria/Gymnodinium complex, with 2 peaks throughout the season. When corrected for processing losses, FISH-based abundance estimates suggest that B. baltica comprised the major fraction of the total dinoflagellate complex during the spring bloom at the southwest coast of Finland.
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| 5. |
- Tahvanainen, Pia, et al.
(författare)
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Patterns of Post-Glacial Genetic Differentiation in Marginal Populations of a Marine Microalga
- 2012
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the genetic structure of an eukaryotic microorganism, the toxic dinoflagellate Alexandrium ostenfeldii, from the Baltic Sea, a geologically young and ecologically marginal brackish water estuary which is predicted to support evolution of distinct, genetically impoverished lineages of marine macroorganisms. Analyses of the internal transcribed spacer (ITS) sequences and Amplified Fragment Length Polymorphism (AFLP) of 84 A. ostenfeldii isolates from five different Baltic locations and multiple external sites revealed that Baltic A. ostenfeldii is phylogenetically differentiated from other lineages of the species and micro-geographically fragmented within the Baltic Sea. Significant genetic differentiation (FST) between northern and southern locations was correlated to geographical distance. However, instead of discrete genetic units or continuous genetic differentiation, the analysis of population structure suggests a complex and partially hierarchic pattern of genetic differentiation. The observed pattern suggests that initial colonization was followed by local differentiation and varying degrees of dispersal, most likely depending on local habitat conditions and prevailing current systems separating the Baltic Sea populations. Local subpopulations generally exhibited low levels of overall gene diversity. Association analysis suggests predominately asexual reproduction most likely accompanied by frequency shifts of clonal lineages during planktonic growth. Our results indicate that the general pattern of genetic differentiation and reduced genetic diversity of Baltic populations found in large organisms also applies to microscopic eukaryotic organisms.
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| 6. |
- Vehmaa, Anu, et al.
(författare)
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Copepod reproductive success in spring-bloom communities with modified diatom and dinoflagellate dominance
- 2012
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Ingår i: ICES Journal of Marine Science. - : Oxford University Press (OUP). - 1054-3139 .- 1095-9289. ; 69:3, s. 351-357
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Tidskriftsartikel (refereegranskat)abstract
- Dinoflagellates have increased and diatoms decreased in the Baltic Sea in recent decades, possibly because of changes in the climate and altered patterns of stratification. The hypothesis that grazing copepods would benefit from the change in species composition was tested experimentally by studying the reproductive output of the crustacean copepod Eurytemora affinis in five Baltic Sea phytoplankton spring communities dominated by different dinoflagellates (Biecheleria baltica, Gymnodinium corollarium) and diatoms (Chaetoceros cf. wighamii, Skeletonema marinoi, and Thalassiosira baltica). After a 5-d acclimation and a 4-d incubation, egg production, egg hatching success, and the RNA: DNA ratio of E. affinis were measured. Egg production was highest on a G. corollarium-dominated diet and lowest on a S. marinoi-dominated diet and on a B. baltica-dominated natural spring bloom, but there were no differences in hatching success. The results demonstrate strong species-specific effects unconstrained by the dominating group. Hence, the hypothesis of specific effects derived from a diatom or dinoflagellate diet is too simplistic, and there is a need to explore phytoplankton taxa at a species level to reveal the reasons for copepod reproductive success.
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