| 1. |
- Flaviani, Flavia, et al.
(författare)
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Distinct Oceanic Microbiomes From Viruses to Protists Located Near the Antarctic Circumpolar Current
- 2018
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Ingår i: Frontiers in Microbiology. - : FRONTIERS MEDIA SA. - 1664-302X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Microbes occupy diverse ecological niches and only through recent advances in next generation sequencing technologies have the true microbial diversity been revealed. Furthermore, lack of perceivable marine barriers to genetic dispersal (i.e., mountains or islands) has allowed the speculation that organisms that can be easily transported by currents and therefore proliferate everywhere. That said, ocean currents are now commonly being recognized as barriers for microbial dispersal. Here we analyzed samples collected from a total of six stations, four located in the Indian Ocean, and two in the Southern Ocean. Amplicon sequencing was used to characterize both prokaryotic and eukaryotic plankton communities, while shotgun sequencing was used for the combined environmental DNA (eDNA), microbial eDNA (meDNA), and viral fractions. We found that Cyanobacteria dominated the prokaryotic component in the South-West Indian Ocean, while gamma-Proteobacteria dominated the South-East Indian Ocean. A combination of gamma- and alpha-Proteobacteria dominated the Southern Ocean. Alveolates dominated almost exclusively the eukaryotic component, with variation in the ratio of Protoalveolata and Dinoflagellata depending on station. However, an increase in haptophyte relative abundance was observed in the Southern Ocean. Similarly, the viral fraction was dominated by members of the order Caudovirales across all stations; however, a higher presence of nucleocytoplasmic large DNA viruses (mainly chloroviruses and mimiviruses) was observed in the Southern Ocean. To our knowledge, this is the first that a statistical difference in the microbiome (from viruses to protists) between the subtropical Indian and Southern Oceans. We also show that not all phylotypes can be found everywhere, and that meDNA is not a suitable resource for monitoring aquatic microbial diversity.
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| 2. |
- Hillebrand, Helmut, et al.
(författare)
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Decomposing multiple dimensions of stability in global change experiments
- 2018
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 21:1, s. 21-30
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Tidskriftsartikel (refereegranskat)abstract
- Ecological stability is the central framework to understand an ecosystem's ability to absorb or recover from environmental change. Recent modelling and conceptual work suggests that stability is a multidimensional construct comprising different response aspects. Using two freshwater mesocosm experiments as case studies, we show how the response to single perturbations can be decomposed in different stability aspects (resistance, resilience, recovery, temporal stability) for both ecosystem functions and community composition. We find that extended community recovery is tightly connected to a nearly complete recovery of the function (biomass production), whereas systems with incomplete recovery of the species composition ranged widely in their biomass compared to controls. Moreover, recovery was most complete when either resistance or resilience was high, the latter associated with low temporal stability around the recovery trend. In summary, no single aspect of stability was sufficient to reflect the overall stability of the system.
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| 3. |
- Hylander, Samuel, et al.
(författare)
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Climate-induced input of turbid glacial meltwater affects vertical distribution and community composition of phyto- and zooplankton
- 2011
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 33:8, s. 1239-1248
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Tidskriftsartikel (refereegranskat)abstract
- Receding glaciers are among the most obvious changes caused by global warming, and glacial meltwater entering lakes generally forms plumes of particles. By taking vertical samples along a horizontal gradient from such a particle source, we found that photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) attenuated 20-25% faster close to the inflow of suspended particles compared with the more transparent part of the gradient. All sampled stations had a deep chlorophyll a (Chl a) maximum at 15-20 m which was more distinct in the transparent part of the horizontal gradient. Picocyanobacteria increased in abundance in more transparent water and their numbers were tightly correlated with the intensity of the deep Chl a maxima. Motile species of phytoplankton had a deeper depth distribution in transparent versus less transparent water. Yet other species, like Chrysochromulina parva, that can withstand high PAR intensities and low nutrient concentrations, increased in abundance as the water became more transparent. Also copepods increased in abundance, indicating that they are more successful in transparent water. We conclude that sediment input into lakes creates horizontal gradients in PAR and UVR attenuation which strongly affect both distribution and behavior of phyto-and zooplankton. The input of glacial flour creates a sub-habitat that can function as a refuge for species that are sensitive to high PAR and UVR exposure. When the glacier has vanished, this habitat may disappear. During the melting period, with heavy sediment input, we predict that competitive species in transparent waters, like Chrysocromulina, picocyanobacteria and copepods, will become less common. The deep Chl a maxima is also likely to become less developed. Hence, glacier melting will probably have profound effects on both species composition and behavior of several planktonic taxa with potential effects on the food web.
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| 4. |
- Johansson, Karin, et al.
(författare)
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Zooplankton Feeding on the Nuisance Flagellate Gonyostomum semen
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:5, s. e62557-
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Tidskriftsartikel (refereegranskat)abstract
- The large bloom-forming flagellate Gonyostomum semen has been hypothesized to be inedible to naturally occurring zooplankton due to its large cell size and ejection of long slimy threads (trichocysts) induced by physical stimulation. In a grazing experiment using radiolabelled algae and zooplankton collected from lakes with recurring blooms of G. semen and lakes that rarely experience blooms, we found that Eudiaptomus gracilis and Holopedium gibberum fed on G. semen at high rates, whereas Daphnia cristata and Ceriodaphnia spp. did not. Grazing rates of E. gracilis were similar between bloom-lakes and lakes with low biomass of G. semen, indicating that the ability to feed on G. semen was not a result of local adaptation. The high grazing rates of two of the taxa in our experiment imply that some of the nutrients and energy taken up by G. semen can be transferred directly to higher trophic levels, although the predominance of small cladocerans during blooms may limit the importance of G. semen as a food resource. Based on grazing rates and previous observations on abundances of E. gracilis and H. gibberum, we conclude that there is a potential for grazer control of G. semen and discuss why blooms of G. semen still occur.
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| 5. |
- Jönsson, Mikael, et al.
(författare)
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Glacial clay affects foraging performance in a Patagonian fish and cladoceran
- 2011
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 663:1, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is altering temperatures and precipitation patterns all over the world. In Patagonia, Argentina, predicted increase in precipitation together with rapidly melting glaciers increase the surface runoff, and thereby the transport of suspended solids to recipient lakes. Suspended solids affect the visual conditions in the water which in turn restricts visual foraging. The native fish Aplochiton zebra Jenyns, and its filter-feeding cladoceran prey, Daphnia commutata Ekman, were subjected to foraging experiments at three turbidity levels. A. zebra foraging rate was substantially reduced at naturally occurring turbidity levels and the filtering rate of D. commutata was reduced at the highest turbidity level. This indicates that Daphnia may be partly released from predation from A. zebra at the same time as it can maintain relatively high feeding rates as turbidity increases. Lower foraging rates at the same time as the metabolic demand increases, through increased temperatures, may result in larger effects on A. zebra than could be expected from increases in turbidity or temperature alone. Turbidity may, as an indirect effect of climate change, decrease planktivore foraging rates and thereby alter the interaction strength between trophic levels.
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| 6. |
- Leblond, Jeffrey D., et al.
(författare)
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Sterols of the Green-Pigmented, Freshwater Raphidophyte, Gonyostomum semen, from Scandinavian Lakes
- 2013
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Ingår i: Journal of Eukaryotic Microbiology. - : Wiley. - 1066-5234 .- 1550-7408. ; 60:4, s. 399-405
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Tidskriftsartikel (refereegranskat)abstract
- Sterols are a class of membrane-reinforcing, ringed lipids which have a long history of examination in algae as a means of deriving chemotaxonomic relationships and as potential lipidic biomarkers. The Raphidophyceae represent a class of harmful, bloom-forming, marine and freshwater algae. To date, there have been four published examinations of their sterol composition, focusing primarily on brown-pigmented, marine species within the genera, Chattonella, Fibrocapsa, and Heterosigma. Lacking in these examinations has been the species Gonyostomum semen Ehrenb., which is a green-pigmented, freshwater raphidophyte with a worldwide distribution. The goal of this study was to examine the sterol composition of this nuisance alga, determine the potential of using its sterol profile as a biomarker, and finally to determine if there is any intraspecific variability between isolates. We have examined 21 isolates of G. semen from a number of Scandinavian lakes, and all were found to produce two major sterols, 24-ethylcholesta-5,22E-dien-3-ol and 24-ethylcholest-5-en-3-ol, and 24-methylcholest-5-en-3-ol as a minor sterol; the presence of 24-ethylcholesta-5,22E-dien-3-ol differentiates G. semen from brown-pigmented, marine raphidophytes which generally lack it. The results of this study indicate that isolates of G. semen from geographically separate lakes across Finland and Scandinavia have the same sterol biosynthetic pathway, and that there is no evolutionary divergence between the isolates with regard to sterol composition. The sterols of G. semen are not considered to be useful biomarkers for this particular organism because they are commonly found in other algae and plants.
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| 7. |
- Lebret, Karen
(författare)
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A Phytoplankton Invasion: Population Genetics, Phylogeography, and Invasion Success of Gonyostomum semen
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- nvasive species is a major threat to ecosystems and biodiversity. Invasions by macroorganisms have been intensively studied, but little is known concerning microbial invasions. In aquatic environments, phytoplankton, i.e. autotrophic microbes, have a key role as primary producers. In my thesis, I focused on the population genetic structure and phylogeography of the freshwater raphidophyte Gonyostomum semen, which is nowadays considered invasive in Northern Europe, as it has increased in abundance and occurence during the last decades. Phytoplankton blooms were for a long time believed to be monoclonal, however recent studies have shown that phytoplankton blooms are highly diverse. G. semen can form blooms in lakes for extended periods of time. In the first study, I investigated the population genetic structure and genetic diversity of G. semen in one lake over time, covering the different stages of the bloom using Amplified Fragment Lenght Polymorphism (AFLP). The genetic diversity of G. semen increased over time, especially at the beginning of the bloom. This increase was likely due to the recruitment of cysts from the sediment bringing new genotypes to the population. The blooms from two consecutive years formed a single genetic population, although a significant differentiation was detected. The results of this study highlight the importance of life cycle characteristics for the intraspecific genetic diversity of partially asexual organisms. In the second study, I investigated the population genetic structure of G. semen in 11 lakes in Northern Europe using AFLP. I found that all the strains isolated from 11 lakes belong to a single genetic population, although significant differentiation was dectected between the sampling locations. The differentiation between locations was likely caused by founder effect following the colonization of the lakes. In addition, low genetic diversity was measured at each location, which could reflect the recent establishment of G. semen in the lakes. These results suggest that the colonization of G. semen in these lakes is relatively recent, and that G. semen has colonized new lakes. In addition, I performed a phylogeographic analysis with strains from 15 Northern European lakes, and two Japanese strains, by sequencing four DNA regions. All the strains from Northern Europe have identical sequences for the four markers. For one marker, the mitochondrial gene cox1, clear differences were detected between the sequences of the Japanese strains and the Northern European ones. In this study the low diversity observed in Northern Europe also support the hypothesis of recent expansion of G. semen. The results of these two studies are coherent with monitoring data suggesting recent invasion of new lakes by G. semen in Northern Europe. Several factors can potentially facilitate the invasion by a species. The absence of a grazer for instance might facilitate the formation of a dense population of an invader. In G. semen, due to its large cell size and mucilage production, the grazing pressure was expected to be low. I performed grazing experiments to determine which potential grazers could feed on G. semen. I found that only the large cladoceran Daphnia magna was able to feed on G. semen. The large cell size of G. semen was likely limiting the grazing by smaller cladocerans, furtermore the mucilage production and expulsion of trichocsyts were likely limiting the feeding of copepods. Field data revealed that the large cladoceran D. magna do not co-exist in G. semen lakes. Thus the grazing pressure on G. semen is likely restricted, allowing the formation of dense populations, and potentially the establishment after colonization of new lakes.
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| 8. |
- Lebret, Karen, et al.
(författare)
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Choice of molecular barcode will affect species prevalence but not bacterial community composition
- 2016
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Ingår i: Marine Genomics. - : Elsevier BV. - 1874-7787 .- 1876-7478. ; 29, s. 39-43
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The rapid advancement of next generation sequencing protocols in recent years has led to the diversification in the methods used to study microbial communities; however, how comparable the data generated from these different methods are, remains unclear. In this study we compared the taxonomic composition and seasonal dynamics of the bacterial community determined by two distinct 16s amplicon sequencing protocols: sequencing of the V6 region of the 16s rRNA gene using 454 pyrosequencing vs the V4 region of the 16s rRNA gene using the Illumina Hiseq 2500 platform. Significant differences between relative abundances at all taxonomic levels were observed; however, their seasonal dynamics between phyla were largely consistent between methods. This study highlights that care must be taken when comparing datasets generated from different methods.
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| 9. |
- Lebret, Karen, et al.
(författare)
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Genetic diversity within and genetic differentiation between blooms of a microalgal species
- 2012
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 14:9, s. 2395-2404
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Tidskriftsartikel (refereegranskat)abstract
- The field of genetic diversity in protists, particularly phytoplankton, is under expansion. However, little is known regarding variation in genetic diversity within populations over time. The aim of our study was to investigate intrapopulation genetic diversity and genetic differentiation in the freshwater bloom-forming microalga Gonyostomum semen (Raphidophyceae). The study covered a 2-year period including all phases of the bloom. Amplified fragment length polymorphism (AFLP) was used to determine the genetic structure and diversity of the population. Our results showed a significant differentiation between samples collected during the two blooms from consecutive years. Also, an increase of gene diversity and a loss of differentiation among sampling dates were observed over time within a single bloom. The latter observations may reflect the continuous germination of cysts from the sediment. The life cycle characteristics of G. semen, particularly reproduction and recruitment, most likely explain a high proportion of the observed variation. This study highlights the importance of the life cycle for the intraspecific genetic diversity of microbial species, which alternates between sexual and asexual reproduction.
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| 10. |
- Lebret, Karen, et al.
(författare)
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Grazing resistance allows bloom formation and may explain invasion success of Gonyostomum semen
- 2012
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 57:3, s. 727-734
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Tidskriftsartikel (refereegranskat)abstract
- The nuisance alga Gonyostomum semen (Raphidophyceae) has expanded in the Nordic countries during the last decades and can dominate lake phytoplankton communities almost completely. A possible explanation to its dominance could be limited grazing by zooplankton. We investigated the potential grazing pressure on G. semen using an experimental approach supported by field data. We determined the grazing rate by cladocerans, calanoid copepods, and Chaoborus larvae to determine which were able to feed on G. semen. Only the large cladoceran Daphnia magna was able to feed successfully on G. semen. The large cell size of G. semen was likely a limiting factor for the filtering apparatus of smaller cladocerans. The copepod Eudiaptomus gracilis did not graze on G. semen, although the mechanism behind this selective feeding is still unknown. In addition to the experimental study, we quantified the zooplankton and phytoplankton communities in 40 lakes to determine the composition and abundance of the zooplankton communities co-occurring with G. semen, suggesting that large cladoceran species were not present in lakes where G. semen occurred. Hence, the growth of G. semen is not significantly controlled by grazing in natural systems, which likely facilitates bloom formation and invasion success of G. semen.
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