| 1. |
- Björnerås, Caroline, et al.
(author)
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Inland blue holes of The Bahamas - chemistry and biology in a unique aquatic environment
- 2020
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In: Fundamental and Applied Limnology. - : Schweizerbart science publishers. - 1863-9135. ; 194:2, s. 95-106
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Journal article (peer-reviewed)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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| 2. |
- Gollnisch, Raphael, et al.
(author)
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Calcium and pH interaction limits bloom formation and expansion of a nuisance microalga
- 2021
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In: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590.
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Journal article (peer-reviewed)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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| 3. |
- Gollnisch, Raphael, et al.
(author)
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Sag-rad : A Method for Single-Cell Population Genomics of Unicellular Eukaryotes
- 2023
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In: Molecular biology and evolution. - 0737-4038. ; 40:5
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Journal article (peer-reviewed)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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| 4. |
- Gollnisch, Raphael, et al.
(author)
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Single-cell genomics of a bloom-forming phytoplankton species reveals population genetic structure across continents
- 2024
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In: The Isme Journal. - 1751-7362. ; 18:1
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Journal article (peer-reviewed)abstract
- The study of microbial diversity over time and space is fundamental to the understanding of their ecology and evolution. The underlying processes driving these patterns are not fully resolved but can be studied using population genetic approaches. Here we investigated the population genetic structure of Gonyostomum semen, a bloom-forming phytoplankton species, across two continents. The species appears to be expanding in Europe, whereas similar trends are not observed in the USA. Our aim was to investigate if populations of Gonyostomum semen in Europe and in the USA are genetically differentiated, if there is population genetic structure within the continents, and what the potential drivers of differentiation are. To this end, we used a novel method based on single-amplified genomes combined with Restriction-site Associated DNA sequencing that allows de novo genotyping of natural single-cell isolates without the need for culturing. We amplified over 900 single-cell genomes from 25 lake populations across Europe and the USA and identified two distinct population clusters, one in Europe and another in the USA. Low genetic diversity in European populations supports the hypothesized recent expansion of Gonyostomum semen on this continent. Geographic population structure within each continent was associated with differences in environmental variables that may have led to ecological divergence of population clusters. Overall, our results show that single-amplified genomes combined with Restriction-site Associated DNA sequencing can be used to analyze microalgal population structure and differentiation based on single-cell isolates from natural, uncultured samples.
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| 5. |
- Gollnisch, Raphael
(author)
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Single-cell population genetics and dispersal limitation of a bloom-forming microalga
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Microalgal range expansions are increasing in frequency and magnitude worldwide mostly due to anthropogenic factors. However, they often remain unnoticed until mass development (algal blooms) occurs due to difficulties in detection when population densities are low. However, population genetic methods offer an approach to investigate these patterns. One such potentially expanding bloom-forming species is the freshwater raphidophyte Gonyostomum semen. It occurs worldwide, and the question regarding whether the species is actually expanding its range is unanswered.In this thesis, I investigated the environmental distribution and population structure of G. semen on a wide geographic scale. My main aims were to 1) reveal patterns of dispersal and genetic divergence of G. semen populations both in Europe and in North America, 2) identify environmental factors that might pose a barrier to G. semen dispersal and expansion, and 3) develop a method for single-cell population genomics of uncultured microeukaryotes to achieve the first aim.Using a population genomic approach known as Restriction-site Associated DNA (RAD) sequencing, a distinct genetic structure of the G. semen populations in Scandinavia and Finland was detected. The data showed a division into a western and an eastern population cluster that probably represent different lineages. While a pattern of recent northward dispersal was expected, the data showed gene flow from the northeast/east to the southwest/west. This genetic signature suggests that the observed gene flow may be due to dispersal by fall migratory birds, which act as dispersal vectors for resistant cysts that form at the end of G. semen blooms.Population genetics in protists is severely hampered by the need to culture strains of clonal isolates to obtain enough DNA to construct a genomic library. I therefore developed a novel method consisting of Single Amplified Genome (SAG) analysis followed by RAD. I used the combination of both techniques, SAG-RAD, to enable de novo genotyping of natural single cell isolates. The method was successfully tested and applied on G. semen.Using the SAG-RAD method the population genetic structure of G. semen was studied across Europe and the United States. Two distinct population clusters were distinguished, one in Europe and one in the United States, with higher genetic similarity within than between continents. The low genetic diversity in the European populations supports the assumption that G. semen has only recently expanded on this continent. Geographic population structure within each continent was associated with differences in environmental factors, while geographic distance played a more limited role.Environmental variables that inhibit the dispersal of G. semen may include, for example, alkalinity. G. semen occurrence, especially in northern Europe, is associated with acidic, mesotrophic brown lakes. In a mesocosm study as well as in a laboratory experiment, G. semen growth was inhibited by high pH in combination with high calcium concentration. From this I concluded that alkaline environments are an important barrier to G. semen colonization. Iron, an important environmental factor associated with increasing lake browning is also an important growth factor for G. semen. Laboratory experiments demonstrated that G. semen required high iron levels in the lake environment and favor the formation of high-density G. semen blooms in boreal brown colored lakes.Altogether, my thesis work demonstrated how population genetic approaches can be used to shed light on past expansions of microbial species, and that it can be achieved without the need for culturing.
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| 6. |
- Lee, Marcus, et al.
(author)
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Low-latitude zooplankton pigmentation plasticity in response to multiple threats
- 2019
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In: Royal Society Open Science. - : Royal Society Open Science. - 2054-5703. ; 6:7, s. 1-10
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Journal article (peer-reviewed)abstract
- Crustacean copepods in high-latitude lakes frequently alter their pigmentation facultatively to defend themselves against prevailing threats, such as solar ultraviolet radiation ( UVR) and visually oriented predators. Strong seasonality in those environments promotes phenotypic plasticity. To date, no one has investigated whether low-latitude copepods, experiencing continuous stress from UVR and predation threats, exhibit similar inducible defences. We here investigated the pigmentation levels of Bahamian 'blue hole' copepods, addressing this deficit. Examining several populations varying in predation risk, we found the lowest levels of pigmentation in the population experiencing the highest predation pressure. In a laboratory experiment, we found that, in contrast with our predictions, copepods from these relatively constant environments did show some changes in pigmentation subsequent to the removal of UVR; however, exposure to water from different predation regimes induced minor and idiosyncratic pigmentation change. Our findings suggest that low-latitude zooplankton in inland environments may exhibit reduced, but non-zero, levels of phenotypic plasticity compared with their high-latitude counterparts.
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| 7. |
- Münzner, Karla, 1989-, et al.
(author)
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High Iron Requirements for Growth in the Nuisance Alga Gonyostomum semen (Raphidophyceae)
- 2021
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In: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 57:4, s. 1309-1322
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Journal article (peer-reviewed)abstract
- The bloom-forming freshwater alga Gonyostomum semen is associated with acidic, mesotrophic brown water lakes in boreal regions. However, researchers have been unable to conclusively link G. semen abundance and bloom formation to typical brown water lake traits, that is, high water color and DOC (dissolved organic carbon) concentrations. Iron is a main driver of water color in boreal lakes, and a recent study of lake monitoring data indicated a connection between lakes with high G. semen abundance and iron concentrations >200 µg · L−1. Thus, iron may be the missing link in explaining G. semen abundance and growth dynamics. We experimentally assessed the effects of different iron concentrations above or below 200 µg · L−1 on the growth of G. semen batch monocultures. Iron concentrations <200 µg · L−1 limited G. semen growth, while iron concentrations >200 µg · L−1 did not. Moreover, the iron concentration of the medium required for growth was higher than for other common phytoplankton (Microcystis botrys and Chlamydomonas sp.) included in the experiment. These results indicate that G. semen requires high levels of iron in the lake environment. Consequently, this and previous findings using lake monitoring data support the hypothesis that high concentrations of iron favor the formation of high-density G. semen blooms in boreal brown water lakes. As lakes get browner in a changing climate, monitoring iron levels could be a potential tool to identify lakes at risk for G. semen blooms, especially among lakes that provide ecosystem services to society.
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| 8. |
- Pärssinen, Varpu, et al.
(author)
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Variation in predation regime drives sex-specific differences in mosquitofish foraging behaviour
- 2021
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In: Oikos. - : Wiley-Blackwell. - 0030-1299 .- 1600-0706. ; 130:5, s. 790-797
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Journal article (peer-reviewed)abstract
- Predation is a well-studied driver of ecological selection on prey traits, which frequently drives divergence in anti-predator performance across environments that vary in predation risk. However, predation also alters prey mortality regimes, where low predation risk often results in higher prey densities and consequently higher intensities of intraspecific resource competition. In addition, predation risk alters the foraging context, as acquiring food can be risky in the presence of predators. Thus, different predation regimes can drive divergent selection on traits associated with resource competition, such as foraging behaviours. Moreover, because sexes often differ in susceptibility to predation and limitations to their reproductive output, the intensity of the tradeoff between predator avoidance and resource competition may depend on sex. We used a laboratory experiment to assess key aspects of foraging performance in a predator-free context in Bahamas mosquitofish Gambusia hubbsi wild-caught from multiple populations that experience either high or low levels of predation risk. When competing for limited food resources at a common density, females from low-predation regimes showed higher foraging and food consumption rates than females from high-predation regimes. Males showed fewer differences between predation regimes, and an opposite pattern from females. We suggest these sex-specific effects result from females facing a greater tradeoff between predation risk and resource competition, combined with males from high-predation environments elevating foraging behaviours in the absence of nearby predators and females. Females of this species are larger than males, bear live young and show higher foraging rates in the wild than males. On the other hand, males spend more time pursuing females in the wild, and may exhibit greater flexibility in foraging behaviours based on the immediate context. Our results show that varying levels of predation risk can lead to differences in behaviours associated with resource competition, but these effects can strongly differ between sexes.
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| 9. |
- Rengefors, Karin, et al.
(author)
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Genome-wide single nucleotide polymorphism markers reveal population structure and dispersal direction of an expanding nuisance algal bloom species
- 2021
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In: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 30:4, s. 912-925
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Journal article (peer-reviewed)abstract
- Species invasion and range expansion are currently under scrutiny due to increasing anthropogenic impact on the natural environment. This is also true for harmful algal blooms, which have been reported to have increased in frequency. However, this research is challenging due to the ephemeral nature, small size and mostly low concentrations of microalgae in the environment. One such species is the nuisance microalga Gonyostomum semen (Raphidophyceae), which has increased in occurrence in northern Europe in recent decades. The question of whether the species has expanded its habitat range or if it was already present in the lakes but was too rare to be detected remains unanswered. The aim of the present study was to determine the genetic structure and dispersal pathways of G. semen using RAD (restriction-site-associated DNA) tag sequencing. For G. semen, which has a huge genome (32 Gbp), we faced particular challenges, but were nevertheless able to recover over 1000 single nucleotide polymorphisms at high coverage. Our data revealed a distinct population genetic structure, demonstrating a divide of western and eastern populations that probably represent different lineages. Despite significant genetic differentiation among lakes, we found only limited isolation-by-distance. While we had expected a pattern of recent expansion northwards, the data demonstrated gene flow from the northeast/east towards the southwest/west. This genetic signature suggests that the observed gene flow may be due to dispersal by autumn migratory birds, which act as dispersal vectors of resistant resting propagules that form at the end of the G. semen blooms.
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| 10. |
- Scharnweber, Kristin, 1983-, et al.
(author)
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Comprehensive analysis of chemical and biological problems associated with browning agents used in aquatic studies
- 2021
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In: Limnology and Oceanography. - : Wiley. - 1541-5856. ; 19:12, s. 818-835
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Journal article (peer-reviewed)abstract
- Inland waters receive and process large amounts of colored organic matter from the terrestrial surroundings. These inputs dramatically affect the chemical, physical, and biological properties of water bodies, as well as their roles as global carbon sinks and sources. However, manipulative studies, especially at ecosystem scale, require large amounts of dissolved organic matter with optical and chemical properties resembling indigenous organic matter. Here, we compared the impacts of two leonardite products (HuminFeed and SuperHume) and a freshly derived reverse osmosis concentrate of organic matter in a set of comprehensive mesocosm- and laboratory-scale experiments and analyses. The chemical properties of the reverse osmosis concentrate and the leonardite products were very different, with leonardite products being low and the reverse osmosis concentrate being high in carboxylic functional groups. Light had a strong impact on the properties of leonardite products, including loss of color and increased particle formation. HuminFeed presented a substantial impact on microbial communities under light conditions, where bacterial production was stimulated and community composition modified, while in dark potential inhibition of bacterial processes was detected. While none of the browning agents inhibited the growth of the tested phytoplankton Gonyostomum semen, HuminFeed had detrimental effects on zooplankton abundance and Daphnia reproduction. We conclude that the effects of browning agents extracted from leonardite, particularly HuminFeed, are in sharp contrast to those originating from terrestrially derived dissolved organic matter. Hence, they should be used with great caution in experimental studies on the consequences of terrestrial carbon for aquatic systems.
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