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Sirvi Autor "Kisand, Veljo (advisor)" järgi

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  • Pisipilt
    Kirje
    From microscopy to genes – tracing toxic cyanobacteria in a shallow eutrophic lake
    (Estonian University of Life Sciences, 2022) Panksep, Kristel; Kisand, Veljo (advisor); Agasild, Helen (advisor); Sivonen, Kaarina (advisor); Institute of Agricultural and Environmental Sciences; Vasas, Gabor (opponent)
    Global warming paired with eutrophication processes is shifting phytoplankton communities towards the dominance of bloom-forming and potentially toxic cyanobacteria. Cyanobacterial blooms are considered an increasing threat in freshwater. Traditional monitoring predominantly relies on cyanobacterial biomass as an indicator of potential toxin presence, disregarding that toxin concentrations can rapidly increase even when cyanobacterial biomass is low. The concentration of toxins in the water is related to the abundance of toxin-producing species and the amount of toxin per cell – toxin quota. My research provides valuable information about the cyanobacterial community composition, the abundance of toxic genotypes, microcystin concentrations, microcystin quota and the environmental factors that promote toxic cyanobacterial blooms in the large and shallow freshwater lake Peipsi. This is the first study to utilise molecular methods as complementary to routine monitoring to determine cyanobacterial toxicity potential in lake Peipsi. In situ studies on zooplankton taxon-specific ingestion of potentially toxic cyanobacteria are still limited. My study focused on the importance of cyanobacteria as a food source for the dominant crustacean grazers. Among the first studies using qPCR targeting cyanobacterial genus-specific mcyE synthase genes in zooplankton gut content analysis, we show that potentially toxic strains of Microcystis can be ingested directly or indirectly by different zooplankton grazers. Information gathered from this study expanded our knowledge on the ecology of toxic cyanobacteria, provided an indication of how molecular methods can improve traditional risk assessment concerning the abundance of cyanobacteria and their cyanotoxins and broadened our knowledge of how target specific molecular tools could be further used in aquatic food-web studies. In the current thesis, I present a synthesis of spatial and temporal variability of potentially toxic cyanobacteria and the importance of cyanobacteria as a food source for crustacean zooplankton in large and shallow lake. The thesis is based on three published papers each dedicated to a different aspect of the whole. This thesis improves our knowledge of potentially toxic cyanobacteria and cyanotoxins in large and shallow eutrophic lakes and also provides the first insight into the in-situ consumption of toxic Microcystis by cladoceran and copepod grazers dominating in the lake. The knowledge gained from this study will guide us to further important questions that should be addressed in future research regarding the functioning of the food web of lake Peipsi. Phytoplankton community through high throughput sequencing would allow analysing the relation of cyanobacterial community composition along with concentration and diversity of cyanotoxins. This would include small-sized cyanobacteria in analysis, which are now excluded from the research. To elucidate the processes underlying cyanotoxin dynamics in more detail, further exploration focusing on the expression of toxin genes along with toxin concentration would be beneficial. Toxin gene expression could better indicate potential risks, especially in water bodies comprising mixed assemblages of toxic and non-toxic cyanobacteria.
  • Pisipilt
    Kirje
    Population genetics of fish host and diplostomid parasites at different scales: from individuals to populations and communities
    (Estonian University of Life Sciences, 2025) Díaz Suárez, Alfonso; Vasemägi, Anti (advisor); Kisand, Veljo (advisor); Noreikiene, Kristina (advisor); Institute of Veterinary Medicine and Animal Sciences; Consuegra del Olmo, Sofia (opponent)
    ABSTRACT. The current biodiversity decline may cause permanent ecosystem disruption. A comprehensive characterisation of biodiversity is essential to forecast potential outcomes. Parasites are the most diverse organisms, but they are often neglected and our knowledge of their diversity is limited. Besides, host-parasite interactions are linked to essential evolutionary processes, shaping biodiversity patters. However, these interactions are highly diverse, differing across individuals, populations, communities as well as at spatial and temporal scales. Novel molecular methods like metabarcoding, which identify multiple species in complex samples, are promising tools for studying parasite diversity and host-parasite interactions. Diplostomid are parasitic flatworms that forms complex communities in fish eyes, which are difficult to identify using microscopy. This thesis studies the genetic diversity of fish host and their diplostomid parasite communities at individual, population and community levels. For that, I study the genetic diversity of anadromous Northern pike in Saaremaa Island and I developed a group-specific metabarcoding method to identify diplostomid species infecting Eurasian perch and common roach. My results revealed that pike in Saaremaa Island consist of genetically divergent populations, varying over tens of kilometres with significant consequences for conservation. Moreover, diplostomid parasite communities in fish are dynamic systems showing variation between host species lakes and site within lakes, suggesting that host-parasite interactions vary at very small spatial scale. Furthermore, I also recorded for the first time, diplostomid brain infection in perch, likely consequence of a density-dependent process. This suggests that infections outside expected locations may be overlooked in wild populations. Overall, my thesis highlights the complex distribution of biodiversity and the associated evolutionary processes in hosts and parasites.