| 71. |
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| 72. |
- Rengefors, Karin
(författare)
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SPECIES ASSEMBLIES AND SEASONAL SUCCESSION OF DINOFLAGELLATES
- 2020
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Ingår i: Dinoflagellates : Classification, Evolution, Physiology and Ecological Significance - Classification, Evolution, Physiology and Ecological Significance. - 9781536178883 - 9781536178890 ; , s. 63-84
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Bokkapitel (refereegranskat)abstract
- Seasonality of dinoflagellate blooms and dinoflagellate assemblies are not random. Yet, bloom events and the specific appearance of species is difficult to predict and sometimes appears stochastic. Nevertheless, it has been established that both abiotic and biotic factors determine species assemblies, as well as the available species pool. The physical environment, especially nutrients and mixing/light depth largely determines when and where dinoflagellates are present. As a response to the environemnt, adaptive strategies (C, S, R) have evolved, allowing different species to be favored in different conditions. Based on functional traits, with cell size being a so called master trait, species can be categorized into different life-forms, which in turn can be predicted for different conditions. Among biotic factors, mortality due to natural enemies, including both grazers and parasites are involved in species succession. In addition both competition among dinoflagellates and with other phytoplankton groups can determine which species occur. Finally, life-cycle transitions, especially for cystproducing (meroplanktonic) species can be used to explain fine-scale species replacement. The latter together with species-specific parasite infections provide promise to untangle the processes behind apparently stochastic events.
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| 73. |
- Rengefors, Karin, et al.
(författare)
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Species-specific alkaline phosphatase activity in freshwater spring phytoplankton: Application of a novel method
- 2001
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 23:4, s. 435-443
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, in situ alkaline phosphatase activity (APA) was studied at the species level in a natural spring community of freshwater phytoplankton. This was achieved by utilizing a substrate called enzyme labeled fluorescence (ELF), which forms fluorescent precipitates at the site of APA. Samples collected from Lake Erken, Sweden, were assayed with ELF and a number of species belonging to Bacillariophyceae, Chlorophyceae and Dinophyceae were labeled. Within these species we found temporal changes in the percentage of the populations that were ELF labeled. Our results demonstrate that species are not all utilizing AP at the same time, and that within one species, individual cells express different levels of APA. Comparisons between ELF activity and bulk community APA measurements, using standard methods, showed cases both of agreement and disagreement. In this study, we were unable to determine whether some of the fragile flagellates were producing AP. These cells were destroyed in the ELF-labeling process. Overall, we found that the ELF method provided new information on APA in freshwater phytoplankton, and that species-specific measurements are possible, but not for all classes of phytoplankton.
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| 74. |
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| 75. |
- Rengefors, Karin, et al.
(författare)
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Temperature as a driver for the expansion of the microalga Gonyostomum semen in Swedish lakes
- 2012
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Ingår i: Harmful Algae. - : Elsevier BV. - 1878-1470 .- 1568-9883. ; 18, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- Gonyostomum semen (Ehrenb) Diesing is a bloom-forming and noxious phytoplankton species, that usually occurs in brown-water lakes and which is often referred to as an invasive species. The aim of our study was to analyze changes over time in the occurrence and distribution of blooms, and to find possible drivers of this change. We also performed spatial analyses to identify environmental factors coupled to Gonyostomum's distribution. The effect of temperature on key processes in the Gonyostomum life cycle was further investigated experimentally to determine potential mechanistic causes. Our results show that G. semen has expanded in Swedish lakes since 1988. At the turn of the Millennium it was present in more than a quarter of the lakes included in the Swedish national lake monitoring program. Gonyostomum-lakes have significantly higher DOC, higher nutrient levels, and lower pH than non-Gonyostomum lakes. Trend analyses show a significant increase in the number of lakes with Gonyostomum, as well as in biomass and occurrence in samples. One explanation is that we more often find water temperatures exceeding 6 degrees C, which is also the threshold for positive growth in our laboratory experiments. Moreover, according to our partial least square regression model (PLS) analysis in one lake, we find that the increase in biomass is a function of temperature in combination with other factors. Thus, we conclude that an increase in water temperature resulting in longer growth season may be a driver of the expansion of Gonyostomum. However, temperature alone cannot explain why the species has expanded to new lakes within the same climatic region. Possibly an interplay between DOC and temperature can explain the patterns observed. (C) 2012 Elsevier B.V. All rights reserved.
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| 76. |
- Rengefors, Karin, et al.
(författare)
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The ecology of freshwater dinoflagellates
- 2018
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Ingår i: Süßwasserflora von Mitteleuropa, Bd. 6: Dinophyceae : Freshwater Flora of Central Europe, Vol. 6: Dinophyceae - Freshwater Flora of Central Europe, Vol. 6: Dinophyceae. - 9783662562680 - 9783662562697 ; 6, s. 27-36
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Bokkapitel (refereegranskat)
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| 77. |
- Rengefors, Karin
(författare)
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The role of resting cysts in the survival and succession of freshwater dinoflagellates
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phytoplankton have adapted to survive in the variable and heterogeneous environment that is characteristic of lakes in temperate regions. One strategy for survival during periods unfavorable for growth is to form resting propagules. Dinoflagellates are bloom-forming phytoplankton which have the ability to form resistant and long-lived resting cysts. The role of cysts in the ecology and life history of dinoflagellates was investigated in this thesis. First, it was tested whether cysts have the ability to assimilate phosphorus (P) during dormancy, which could improve the survival of newly germinated cells when returning to the water column. Secondly, the role of resting cysts in regulating the seasonal succession of dinoflagellates in Lake Erken was examined. Also. biotic and abiotic factorscontrolling the timing of germination were tested.Cysts of the marine dinoflagellate Scrippsiella trochoidea which were incubated in P enriched medium attained a P content twice that of cysts incubated in P deplete medium. Cysts of the freshwater dinoflagellate Ceratium hirundinella had only a slightly higher P content when incubated in P rich medium. Some uptake may be taking place (although adsorption to the cyst wall cannot be excluded), but not enough to provide newly excysted cells with a competitive advantage over other phytoplankton. Phosphorus may, however, play a role in cyst survival and subsequent germination processes.Nine species of dinoflagellates were found in Lake Erken, of which one new thecate phototrophic species, Peridinium euryceps Rengefors et B. Meyer was encountered. This is a cryophilic-and a cyst-forming species, with a distinct and extremely flattened shape. All phototrophic dinoflagellates in Lake Erken rested as cysts during the major part of the year. Timing of germination was mainly regulated by an internal maturation period, a biological clock, and temperature. Furthermore, C. hirundinella cysts did not germinate when incubated in anoxic conditions. Cysts of Peridinium aciculiferum, a winter species, did not germinate in the presence of exudate from zooplankton (predators). These results suggest that cyst dormancy may also be a predator avoidance strategy for some species.To summarize, the results of the studies presented in this thesis show that resting cysts play a significant role in the seasonal succession of dinoflagellates. Also, the cyst stage appears to be a survival strategy for escaping herbivory. Furthermore the results suggest that nutrient uptake may occur during the cyst stage, which in turn can affect the survival of the cyst and the newly germinated cell.
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| 78. |
- Rengefors, Karin, et al.
(författare)
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Toxicity in Peridinium aciculiferum—an adaptive strategy to outcompete other winter phytoplankton?
- 2001
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 46:8, s. 1990-1997
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater dinoflagellates may form dense blooms during winter in ice-covered lakes. Unlike their marine counterparts, freshwater dinoflagellates are rarely considered to be potential toxin producers. Here we tested whether the winter species Peridinium aciculiferum produces a toxin(s) and investigated the potential adaptive function of that toxin, i.e., predator defense or inhibition of competitors (allelopathy). Using traditional toxicity bioassays (Artemia toxicity test and hemolytic activity assay). we detected the production of a toxic substance by P. aciculiferum cells from both the field and from laboratory cultures. Cultures deprived of phosphorus and in stationary phase showed highest toxicity. Potential predators, such as Daphnia galeata (Cladocera) and Eudiaptomus graciloides (Copepoda), were apparently not harmed by P. aciculiferum toxicity. However, the naturally coaccurring competitor Rhodomonas lacustris (Cryptophyceae) was killed by P. aciculiferum. An allelopathic substance(s) caused the cells of R. lacustris to form blisters and subsequently lyse. We concluded that our results support the hypothesis that P. aciculiferum is allelopathic, but not that toxins serve as predator defense. We therefore suggest that allelopathy may be an adaptive strategy of winter dinoflagellates, which could allow them to outcompete other phytoplankton species and thereby dominate the algal biomass.
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| 79. |
- 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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| 80. |
- Sassenhagen, Ingrid, et al.
(författare)
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Germination and colonization success of Gonyostomum semen (Raphidophyceae) cysts after dispersal to new habitats
- 2015
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 37:5, s. 857-861
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Tidskriftsartikel (refereegranskat)abstract
- Colonization of new habitats through dispersal of phytoplankton cysts might be limited, if resident populations outcompete invaders during germination. We reciprocally transferred Gonyostomum semen (Raphidophyceae) cysts from three lakes into native and foreign waters originating from the respective habitats. Germination rate and germling growth were impacted by water origin, but there was no preference for native water. Gonyostomum semen’s ability to germinate in different conditions might explain its expansion in northern Europe.
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