| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- Logares, Ramiro, et al.
(författare)
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Contrasting prevalence of selection and drift in the community structuring of bacteria and microbial eukaryotes
- 2018
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 20:6, s. 2231-2240
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Tidskriftsartikel (refereegranskat)abstract
- Whether or not communities of microbial eukaryotes are structured in the same way as bacteria is a general and poorly explored question in ecology. Here, we investigated this question in a set of planktonic lake microbiotas in Eastern Antarctica that represent a natural community ecology experiment. Most of the analysed lakes emerged from the sea during the last 6000 years, giving rise to waterbodies that originally contained marine microbiotas and that subsequently evolved into habitats ranging from freshwater to hypersaline. We show that habitat diversification has promoted selection driven by the salinity gradient in bacterial communities (explaining approximate to 72% of taxa turnover), while microeukaryotic counterparts were predominantly structured by ecological drift (approximate to 72% of the turnover). Nevertheless, we also detected a number of microeukaryotes with specific responses to salinity, indicating that albeit minor, selection has had a role in the structuring of specific members of their communities. In sum, we conclude that microeukaryotes and bacteria inhabiting the same communities can be structured predominantly by different processes. This should be considered in future studies aiming to understand the mechanisms that shape microbial assemblages.
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| 10. |
- Sassenhagen, Ingrid, et al.
(författare)
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Freshwater protists do not go with the flow: Population structure in Gonyostomum semen independent of connectivity among lakes
- 2015
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 17:12, s. 5063-5072
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Tidskriftsartikel (refereegranskat)abstract
- Many recent studies have found genetically differentiated populations in microorganisms despite potentially high dispersal. We designed a study to specifically examine the importance of physical dispersal barriers, i.e. geographic distance and lack of hydrological connectivity, in restricting gene flow and enhancing divergence in limnic microorganisms. We focused on the nuisance microalga Gonyostomum semen, which has recently expanded in Northern Europe and differentiated into genetically distinct populations. G.semen was sampled from six lakes distributed in two adjacent watersheds, which thereby comprised, both connected and non-connected lakes. The individual isolates were genotyped by amplified fragment length polymorphism. Several lake populations were differentiated from each other, but connectivity within watersheds could not explain the observed population genetic pattern. However, isolation by distance was moderate and might limit the gene flow among distant populations. In addition, we found low, but significant linkage disequilibrium, which indicates regular sexual recombination in this species, despite its high degree of asexual reproduction. Therefore, we conclude that the genetic properties of microalgae with occasional sexual reproduction essentially mirror regularly recombining species. Furthermore, the data indicated bottlenecks supporting the hypothesized recent range expansion of this species.
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