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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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Adaptation mechanisms to wide salinity gradient in algae; transitions between marine and freshwater environments in chrysophytes
Knotek, Petr ; Němcová, Yvonne (advisor) ; Pusztai, Martin (referee)
The transition from the marine to the freshwater environment and vice versa is a key event in the evolution of organisms. Although these transitions are relatively rare from an evolutionary point of view, most large groups of organisms have undergone this event at least once. The marine and freshwater environment differs in many aspects, especially salinity. During the transition between these two environments, the organisms are forced to overcome a significant salinity gradient and adapt to changes in the osmotic potential. However, biotic factors also play an important role, especially competition and predation in the new environment. The aim of the bachelor 's thesis is to provide comprehensive information on the mechanisms of adaptation to a wide gradient of salinity in algae in general and to focus on freshwater-marine transitions in chrysophytes, that occurred repeatedly and relatively frequently in the course of evolution. Key words: chrysophytes, Chrysophyceae, salinity gradient, osmoregulation, marine- freshwater transition
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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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Chrysophycean cysts and scales in paleolimnological studies
Bartošová, Kateřina ; Němcová, Yvonne (advisor) ; Škaloudová, Magda (referee)
This thesis deals with chrysophyte scales and stomatocysts as useful tool of paleoecological reconstructions in lake ecosystems. In the first part the geological physical and biological aspects of lake reconstructions are described. The second part contents information about chrysophyte taxa and their utilisation as paleoekological indicators. Chrysophyte microphosils include two major groups of siliceous indicator: stomatocysts and sculptured and ornamented species-specific scales. Using surface-sediment training sets, quantitative inference models have been constructed for eutrophication, acidification, air-born pollution, salinification, climatic change, and other environmental changes. This thesis represents a literature review.
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