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Genome size variation in microalgae and its evolutionary consequences
Čertnerová, Dora
Eukaryotic organisms exhibit tremendous variability in genome size with no apparent connection to their biological complexity. Although this variation is known to correlate with numerous phenotypic traits, its evolutionary consequences remain widely unknown. This particularly applies to microalgae, where the genome size estimation is often methodologically challenging. Yet, microalgae represent a promising model group to study genome size evolution owing to their lower body complexity, short generation time and large population sizes, the latter two allowing them to quickly respond to environmental challenges. The main aim of this thesis was to enhance our understanding of genome size variation in microalgae and its evolutionary consequences. To do so, together with my co-authors, I summarized the flow cytometry (FCM) protocols used for microalgae and microorganisms possessing small genomes and addressed their limitations resulting mainly from insufficient amounts of biomass, difficulties with nuclei extraction and prominent background noise due to presence of various pigments and secondary metabolites. Further, I provided best practice recommendations that include, among others, analysing young cultures, avoiding long-term cultivation, and testing different isolation buffers and nuclei isolation...
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Genome size variation in microalgae and its evolutionary consequences
Čertnerová, Dora ; Škaloud, Pavel (advisor) ; Boenigk, Jens (referee) ; Bureš, Petr (referee)
Eukaryotic organisms exhibit tremendous variability in genome size with no apparent connection to their biological complexity. Although this variation is known to correlate with numerous phenotypic traits, its evolutionary consequences remain widely unknown. This particularly applies to microalgae, where the genome size estimation is often methodologically challenging. Yet, microalgae represent a promising model group to study genome size evolution owing to their lower body complexity, short generation time and large population sizes, the latter two allowing them to quickly respond to environmental challenges. The main aim of this thesis was to enhance our understanding of genome size variation in microalgae and its evolutionary consequences. To do so, together with my co-authors, I summarized the flow cytometry (FCM) protocols used for microalgae and microorganisms possessing small genomes and addressed their limitations resulting mainly from insufficient amounts of biomass, difficulties with nuclei extraction and prominent background noise due to presence of various pigments and secondary metabolites. Further, I provided best practice recommendations that include, among others, analysing young cultures, avoiding long-term cultivation, and testing different isolation buffers and nuclei isolation...
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Pattern as a functional trait, case study on Mallomonas chrysophytes
Knotek, Petr ; Němcová, Yvonne (advisor) ; Rychtecký, Pavel (referee)
The patterns that can be admired on the surface of many living creatures are also found in many microscopic organisms outside of the macroscopic world we are familiar with. However, their significance and function are yet little understood compared to those of the macroscopic world. In diatoms (Bacillariophyceae) and coccoliths (Haptophyceae), several hypotheses have already been developed concerning the function of their patterned shells. One hypothesis considers the shell as a photonic entity that could reflect UV radiation away from the cell. Others focus more on its mechanical properties, which are among the most impressive within biological structures. Silica-scaled chrysophytes (Synurales, Stramenopiles) also possess a complex shell (or scale-case). Cells are covered with scales (about 4 µm in size) that are very regularly arranged and form a siliceous scale-case on the surface. The pattern on the scales is species-specific and has undergone gradual modification during evolution. This work aims to assess whether the patterning of siliceous scales in the order Synurales can be considered a functional trait or it is a result of neutral evolution. To test the possible photonic properties of the patterned structures, a pair of growth experiments were performed. The experimental cultures were...
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Evolution of silica structures in SAR protists
Čížková, Natálie ; Čertnerová, Dora (advisor) ; Kulichová, Jana (referee)
Silicon is an important element in the earth's crust. In nature it mainly occurs in the form of silicic acid. This element is used by marine and freshwater organisms to form their siliceous structures. The organisms that make up these structures are located throughout the phylogenetic tree and are not limited just to protist groups. The SAR line includes Stramenopila, Alveolata and Rhizaria. The main protist taxa forming the mentioned siliceous structures are in these groups. These are mainly diatoms, silicoflagellates, radiolarians and the group chrysophyceae. The formation of siliceous structures usually provides evolutionary benefits to organisms, such as protection of the cell from actions of biotic and abiotic factors. The availability of dissolved silicon changed during evolution, thus affecting the appearance and functionality of the structures of individual species. Structural changes were manifested by thinning of the shells, change of cell size, enlargement or decrease of pores, increase of the number of thorns or, conversely, their loss. The individual lines thus had to choose the best possible strategies in response to the decreasing availability of silicic acid. Therefore, there was frequent competition between the groups for the remaining dissolved silicon. The current diversity of...
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Adaptive functions of algal resting stages with emphasis on the chrysophyte stomatocysts
Mušálková, Petra ; Němcová, Yvonne (advisor) ; Pusztai, Martin (referee)
Formation of resting stages is a very common feature occurring in most algae classes. Primarily this stage is considered as a resistant form that helps the organism to survive adverse conditions and rapidly changing environment. However, it may also serve to spread as a seed bank to recolonize habitat or can be a source of genetic variation if it follows sexual reproduction. The importance of this dormant benthic stage grows with algae whose population growth is seasonal and the formation of cysts or spores is crucial for them, for instance dinoflagellates and golden algae. Resting stages of Chrysophyceae are called stomatocysts they are produced endogenously and are composed of polymerized silica. Stomatocysts have species-specific morphology. For most described species of Chrysophyceae morphology of the stomatocyst is unknown. Determining the species is difficult especially because of rapid alternation of chrysophyte dominant species in natural waterbodies. So far, it has not been elucidated what factors cause encystation and excystation. Several laboratory experiments has been conducted on this subject. The process of encystation and excystation is assumed to be induced by combination of external and internal factors. Stomatocysts may developed after sexual reproduction or from vegetative cells....
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Reconstructing the evolution and fylogenetic relationships of silica-scaled chrysophyte genus Mallomonas
Čertnerová, Dora ; Škaloud, Pavel (advisor) ; Záveská, Eliška (referee)
The taxonomic concept of the algal genus Mallomonas (Synurales, Synurophyceae) was based on an extraordinary morphological diversity of their siliceous scales. The main aims of this study were elucidation of phylogenetic relationships among its representatives and reconstruction of shape evolution of particular siliceous structures of their scales. Molecular data for six species were acquired for the first time, enabling a successful assessment of their phylogenetic relationships with the other representatives of the genus. On the basis of molecular data, the genus Mallomonas can be divided in two evolutionary lineages and this division is also reflected morphologically (with only a few exceptions) through presence or absence of a V-rib structure. Fine ornamentation of siliceous scales is species-specific and interestingly, the overall differences in morphology of siliceous scales are mostly reflecting phylogenetic relationships among representatives of the genus. In this context, morphological species concept of Mallomonas seems to be justified. Morphologically-based sections of the genus are often paraphyletic, because small sections (frequently containing only single species) tend to be nested within particular larger sections. The main reason for this discrepancy is accelerated morphological...
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