| 51. |
- Logares, Ramiro, et al.
(författare)
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Recent evolutionary diversification of a protist lineage.
- 2008
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 10:5, s. 1231-1243
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Tidskriftsartikel (refereegranskat)abstract
- Here, we have identified a protist (dinoflagellate) lineage that has diversified recently in evolutionary terms. The species members of this lineage inhabit cold-water marine and lacustrine habitats, which are distributed along a broad range of salinities (0–32) and geographic distances (0–18 000 km). Moreover, the species present different degrees of morphological and sometimes physiological variability. Altogether, we analysed 30 strains, generating 55 new DNA sequences. The nuclear ribosomal DNA (nrDNA) sequences (including rapidly evolving introns) were very similar or identical among all the analysed isolates. This very low nrDNA differentiation was contrasted by a relatively high cytochrome b (COB) mitochondrial DNA (mtDNA) polymorphism, even though the COB evolves very slowly in dinoflagellates. The 16 Maximum Likelihood and Bayesian phylogenies constructed using nr/mtDNA indicated that the studied cold-water dinoflagellates constitute a monophyletic group (supported also by the morphological analyses), which appears to be evolutionary related to marine-brackish and sometimes toxic Pfiesteria species. We conclude that the studied dinoflagellates belong to a lineage which has diversified recently and spread, sometimes over long distances, across low-temperature environments which differ markedly in ecology (marine versus lacustrine communities) and salinity. Probably, this evolutionary diversification was promoted by the variety of natural selection regimes encountered in the different environments.
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| 52. |
- Mertens, Kenneth Neil, et al.
(författare)
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A review of recent freshwater dinoflagellate cysts: taxonomy, phylogeny, ecology and palaeocology
- 2012
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Ingår i: Phycologia. - : Informa UK Limited. - 0031-8884 .- 2330-2968. ; 51:6, s. 612-619
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Forskningsöversikt (refereegranskat)abstract
- Resting stages (e.g. cysts) play an important role in the life history and ecology of phytoplankton, e.g. the survival, reproduction, genetic recombination, and dispersal of many species. Marine dinoflagellates cysts have been intensively studied by both geologists and biologists, but freshwater cysts have received less attention. There are approximately 350 freshwater dinoflagellate species, and resting cysts have been described for 84 species. We evaluated the descriptions, and we reproduced images for each cyst type. The review highlighted the importance of cyst characters for taxonomy and phylogeny. We suggested that shape, wall ornamentation and possibly the archeopyle and color were important morphological characteristics at the generic level and above. The ecology of freshwater dinoflagellate cysts was reviewed, and the ecological role of cysts was discussed. The potential of freshwater cysts for Quaternary palaeoecological reconstructions was highlighted, revealing that these could serve as useful indicators of temperature, pH and productivity.
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| 53. |
- Münzner, Karla, 1989-, et al.
(författare)
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High Iron Requirements for Growth in the Nuisance Alga Gonyostomum semen (Raphidophyceae)
- 2021
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Ingår i: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 57:4, s. 1309-1322
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Tidskriftsartikel (refereegranskat)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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| 54. |
- Pärssinen, Varpu, et al.
(författare)
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Variation in predation regime drives sex-specific differences in mosquitofish foraging behaviour
- 2021
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Ingår i: Oikos. - : Wiley-Blackwell. - 0030-1299 .- 1600-0706. ; 130:5, s. 790-797
-
Tidskriftsartikel (refereegranskat)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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| 55. |
- Rengefors, Karin, et al.
(författare)
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Algal cyst dormancy: a temporal escape from herbivory
- 1998
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Ingår i: PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES B-BIOLOGICAL SCIENCES. - 0962-8452. ; 265:1403, s. 1353-1358
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Tidskriftsartikel (refereegranskat)abstract
- Many phytoplankton species form resting cysts and remain dormant for part of the year. The subsequent excystment is regulated by the external environment and internal maturation processes. Here we assessed the excystment of the dinoflagellates Ceratium hi
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| 56. |
- Rengefors, Karin, et al.
(författare)
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Broad allelopathic activity in Peridinium aciculiferum (Dinophyceae)
- 2007
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Ingår i: European Journal of Phycology. - : Informa UK Limited. - 1469-4433 .- 0967-0262. ; 42:4, s. 341-349
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Tidskriftsartikel (refereegranskat)abstract
- The dinoflagellate Peridinium aciculiferum forms blooms underneath the ice in temperate lakes and has previously been shown to have an allelopathic effect on a natural competitor as well as being haemolytic. Hence, we investigated whether P. aciculiferum is allelopathic towards a wide range of different freshwater phytoplankton species. We also tested the hypothesis that nutrient (N and P) deficiency enhances its allelopathic effect. In addition, we explored how target cell density affected the extent of the allelopathic effect. Our findings showed that P. aciculiferum had a negative effect (mortality through lyses) on Synura petersenii (Chrysophyceae), Peridinium inconspicuum (Dinophyceae), Cyclotella sp. (Bacillariophyceae), Cryptomonas sp. and Rhodomonas lacustris (Cryptophyceae). Only Chlamydomonas reinhardtii (Chlorophyceae) cells were not negatively affected. In semi-continuously grown nutrient deficient cultures, we detected no allelopathic activity, in contrast to the findings for batch cultures. Finally, we found that, at donor-target cell ratios above 6:1, the algicidal effect of P. aciculiferum did not increase. We concluded that the allelopathic activity of P. aciculiferum has a wide span of action due to either a single chemical or a cocktail of allelochemicals, but that allelopathic activity is highly variable depending on growth conditions.
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| 57. |
- Rengefors, Karin, et al.
(författare)
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Cell lysis of competitors and osmotrophy enhance growth of the bloom forming alga Gonyostomum semen
- 2008
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 51:1, s. 87-96
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe nuisance alga Gonyostomum semen (Raphidophyceae) is known to form dense blooms in many freshwater bodies, and has increased its distribution and abundance. However, information on the mechanisms behind bloom formation and maintenance is scarce. Field observations indicate that G. semen may be favored in humic lakes, In the present study, we performed controlled laboratory experiments on cultures to test whether G. semen growth is enhanced by humic acids. In addition, we tested the mixotrophic capability of G. semen by providing it with Rhodomonas lacustris as prey. G. semen increased its growth rate in the presence of humic substances due to either acquisition of carbon or some unknown growth factor. Moreover, growth rate was enhanced in the presence of R. lacustris, which in turn was negatively influenced when cultured together with G. semen. We found no evidence of phagotrophy, but observed lysis of R. lacustris cells exposed to G. semen pre-grown with R, lacustris. Thus, our experiments suggest that cell lysis (probably via trichocyst action) and osmotrophy could be 2 mechanisms involved in establishing and maintaining dominance of G. semen in humic lakes.
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| 58. |
- Rengefors, Karin, et al.
(författare)
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Environmental and endogenous regulation of cyst germination in two freshwater dinoflagellates
- 1998
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Ingår i: JOURNAL OF PHYCOLOGY. - : PHYCOLOGICAL SOC AMER INC. - 0022-3646. ; 34:4, s. 568-577
-
Tidskriftsartikel (refereegranskat)abstract
- The role of excystment in relation to seasonal succession was investigated in two freshwater dinoflagellates, Ceratium hirundinella (O.F. Muller) Dujardin and Peridinium aciculiferum (Lemmermann). Field studies and laboratory experiments were performed to
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| 59. |
- Rengefors, Karin, et al.
(författare)
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Evidence of concurrentlocal adaptation and high phenotypic plasticityin a polar microeukaryote.
- 2015
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Ingår i: Environmental Microbiology. - : Wiley. - 1462-2920 .- 1462-2912. ; 17:5, s. 1510-1519
-
Tidskriftsartikel (refereegranskat)abstract
- Here we investigated whether there is evidence of local adaptation in strains of an ancestrallymarine dinoflagellate to the lacustrine environment they now inhabit(optimal genotypes) and/orif they have evolved phenotypic plasticity (a range of phenotypes). Eleven strains of Polarella glacialis were isolated and cultured from three different environments: the polar seas, ahyposaline,and a hypersaline Antarctic lake. Local adaptation was tested by comparing growth rates of lacustrine and marine strains at their own and reciprocal site conditions. To determine phenotypic plasticity, we measured thereaction norm for salinity.We found evidence of both, limitedlocal adaptation andhigherphenotypic plasticity in lacustrine strains when compared tomarine ancestors. At extreme high salinities,local lake strains outperformed otherstrains, and at extreme low salinities, strains from the hyposaline lake outperformed all other strains. The data suggest that lake populations may have evolved higher phenotypic plasticity in the lake habitats compared to the sea, presumably due to the high temporal variability in salinity in the lacustrine systems. Moreover, the interval of salinity tolerance differed between strains from the hyposalineand hypersaline lakes, indicatinglocal adaptation promoted by different salinity.
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| 60. |
- Rengefors, Karin, et al.
(författare)
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Experimental investigation of taxon-specific response of alkaline phosphatase activity in natural freshwater phytoplankton
- 2003
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 48:3, s. 1167-1175
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Tidskriftsartikel (refereegranskat)abstract
- It is widely accepted that alkaline phosphatase activity (APA) is an efficient indicator of phosphate limitation in freshwater phytoplankton communities. In this study, we investigated whether the response in APA to phosphate limitation differs among the taxa in a mixed phytoplankton assemblage. We used the new enzyme-labeled fluorescence (ELF) technique, which allows microscopic detection of phosphate limitation in individual cells of multiple species. The most prominent findings of this study were that alkaline phosphatase (AP) was induced in many, but not all taxa and that different taxa, as well as different cells within a single taxon, experienced different degrees of phosphate stress under the same environmental conditions. Our approach was to manipulate the limiting nutrient in a natural freshwater phytoplankton community by incubating lake water in the laboratory. We induced nitrogen (N) or phosphate limitation through additions of inorganic nutrients. Both the ELF assay and bulk APA indicated that the lake phytoplankton were not phosphate limited at the start of the experiment. During the experiment, several chlorophyte taxa (e.g., Eudorina and an unidentified solitary spiny coccoid) were driven to phosphate limitation when inorganic N was added, as evidenced by a higher percentage of ELF-labeled cells relative to controls, whereas other chlorophyte taxa such as Actinastrum and Dicryosphaerium were not phosphate stressed under these conditions. In the phosphate-limited treatments, little or no ELF labeling was observed in any cyanobacterial taxa. Furthermore, all taxa observed after the ELF labeling procedure (>10-mum fraction) were labeled with ELF at least on one occasion, demonstrating the wide applicability of the ELF method. By using ELF labeling in tandem with bulk APA, the resolution and analysis of phosphate limitation was increased, allowing the identification of specific phosphate-stressed taxa.
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