| 61. |
- Rengefors, Karin, et al.
(författare)
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Factors regulating the recruitment of cyanobacterial and eukaryotic phytoplankton from littoral and profundal sediments
- 2004
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Ingår i: Aquatic Microbial Ecology. - 0948-3055. ; 36:3, s. 213-226
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Tidskriftsartikel (refereegranskat)abstract
- Many phytoplankton species produce resting cysts, forming 'seed banks' on lake sediments until they germinate and provide inocula (recruitment) for future pelagic populations. We have addressed the question of whether the littoral or the profundal zone provides the inoculum for planktonic populations in a eutrophic and dimictic lake (Lake Erken, Sweden). Our hypotheses were that high temperature, light, and sediment mixing would enhance recruitment. Also, we hypothesized that recruitment from littoral sediments would be greater than from profundal sediments. In situ recruitment traps were utilized to compare littoral and profundal recruitment, while laboratory experiments were performed to analyze which factors were most important. Seven common taxa were investigated: Asterionella formosa (Bacillariophyceae), Ceratium hirundinella (Dinophyceae), Microcystis botrys, M. wesenbergii, Anabaena sp., A. solitaria, and A. lemmermannii (Cyanobacteria). Our main findings were that light and sediment mixing were the most important factors in triggering and enhancing recruitment in the laboratory. Temperature and sediment origin (littoral/profundal) had a significant effect on recruitment only for A. lemmermannii and C. hirundinella, respectively. The field experiments showed that recruitment at the littoral site was much higher than at the profundal site, where little or no recruitment occurred. Together, these results strongly suggest that littoral sediments in temperate lakes provide inocula for most phytoplankton populations, likely due to favorable light conditions and high sediment mixing.
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| 62. |
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| 63. |
- Rengefors, Karin, et al.
(författare)
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Genetic diversity and evolution in eukaryotic phytoplankton : Revelations from population genetic studies
- 2017
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 39:2, s. 165-179
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Tidskriftsartikel (refereegranskat)abstract
- Eukaryotic phytoplankton exhibit an enormous species richness, displaying a range of phylogenetic, morphological and physiological diversity. Yet, until recently, very little was known about the diversity, genetic variation and evolutionary processes within species and populations. An approach to explore this diversity and to understand evolution of phytoplankton is to use population genetics as a conceptual framework and methodology. Here, we discuss the patterns, processes and questions that population genetic studies have revealed in eukaryotic phytoplankton. First, we describe the main biological processes generating genetic variation. We specifically discuss the importance of life-cycle complexity for genetic and phenotypic diversity and consider how such diversity can be maintained during blooms when rapid asexual proliferation dominates. Next, we explore how genetic diversity is partitioned over time and space, with a focus on the processes shaping this structure, in particular selection and genetic exchange. Our aim is also to show how population genetics can be used to make inferences about realized dispersal and sexual recombination, as these processes are so difficult to study directly. Finally, we highlight important open questions and suggest promising avenues for future studies that will be made possible by new sequencing technologies.
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| 64. |
- Rengefors, Karin, et al.
(författare)
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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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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 30:4, s. 912-925
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Tidskriftsartikel (refereegranskat)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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| 65. |
- Rengefors, Karin, et al.
(författare)
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Marine-derived dinoflagellates in Antarctic saline lakes: annual dynamics and community composition
- 2008
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Ingår i: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 44:3, s. 592-604
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Tidskriftsartikel (refereegranskat)abstract
- The saline lakes of the Vestfold Hills in Antarctica offer a remarkable natural laboratory where the adaptation of planktonic protists to a range of evolving physiochemical conditions can be investigated. This study illustrates how an ancestral marine community has undergone radical simplification leaving a small number of well-adapted species. Our objective was to investigate the species composition and annual dynamics of dinoflagellate communities in three saline Antarctic lakes. We observed that dinoflagellates occur year-round despite extremely low PAR during the southern winter, which suggests significant mixotrophic or heterotrophic activity. Only a small number of dominant dinoflagellate species were found in each lake, in contrast to the species-rich Southern Ocean from which the lake communities are believed to be derived. We verified that the lake species were representatives of the marine polar dinoflagellate community, and not freshwater species. Polarella glacialis Montresor, Procaccini et Stoecker, a bipolar marine species, was for the first time described in a lake habitat and was an important phototrophic component in the higher salinity lakes. In the brackish lakes, we found a new sibling species to the brackish-water species Scrippsiella hangoei (J. Schiller) J. Larsen, previously observed only in the Baltic Sea.
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| 66. |
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| 67. |
- Rengefors, Karin, et al.
(författare)
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Phosphorus uptake by resting cysts of the marine dinoflagellate Scrippsiella trochoidea
- 1996
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Ingår i: JOURNAL OF PLANKTON RESEARCH. - : OXFORD UNIV PRESS UNITED KINGDOM. - 0142-7873. ; 18:9, s. 1753-1765
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Tidskriftsartikel (refereegranskat)abstract
- Resting cysts of the marine dinoflagellate Scrippsiella trochoidea were produced under phosphorus (P)-deficient conditions, separated from vegatative cells, and incubated for 28 days in darkness at 4 and 20 degrees C in P-enriched and P-deplete medium. Th
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| 68. |
- Rengefors, Karin, et al.
(författare)
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Polar lakes may act as ecological islands to aquatic protists.
- 2012
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Ingår i: Molecular Ecology. - 0962-1083. ; 21:13, s. 3200-3209
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental question in ecology is whether microorganisms follow the same patterns as multicellular organisms when it comes to population structure and levels of genetic diversity. Enormous population sizes, predominately asexual reproduction and presumably high dispersal because of small body size could have profound implications on their genetic diversity and population structure. Here, we have analysed the population genetic structure in a lake-dwelling microbial eukaryote (dinoflagellate) and tested the hypothesis that there is population genetic differentiation among nearby lake subpopulations. This dinoflagellate occurs in the marine-derived saline lakes of the Vestfold Hills, Antarctica, which are ice-covered most of the year. Clonal strains were isolated from four different lakes and were genotyped using amplified fragment length polymorphism (AFLP). Our results show high genetic differentiation among lake populations despite their close geographic proximity (<9 km). Moreover, genotype diversity was high within populations. Gene flow in this system is clearly limited, either because of physical or biological barriers. Our results discard the null hypothesis that there is free gene flow among protist lake populations. Instead, limnetic protist populations may differentiate genetically, and lakes act as ecological islands even on the microbial scale.
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| 69. |
- Rengefors, Karin, et al.
(författare)
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Population genomic analyses reveal that salinity and geographic isolation drive diversification in a free-living protist
- 2024
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Ingår i: Scientific Reports. - 2045-2322. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Protists make up the vast diversity of eukaryotic life and play a critical role in biogeochemical cycling and in food webs. Because of their small size, cryptic life cycles, and large population sizes, our understanding of speciation in these organisms is very limited. We performed population genomic analyses on 153 strains isolated from eight populations of the recently radiated dinoflagellate genus Apocalathium, to explore the drivers and mechanisms of speciation processes. Species of this genus inhabit both freshwater and saline habitats, lakes and seas, and are found in cold temperate environments across the world. RAD sequencing analyses revealed that the populations were overall highly differentiated, but morphological similarity was not congruent with genetic similarity. While geographic isolation was to some extent coupled to genetic distance, this pattern was not consistent. Instead, we found evidence that the environment, specifically salinity, is a major factor in driving ecological speciation in Apocalathium. While saline populations were unique in loci coupled to genes involved in osmoregulation, freshwater populations appear to lack these. Our study highlights that adaptation to freshwater through loss of osmoregulatory genes may be an important speciation mechanism in free-living aquatic protists.
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| 70. |
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