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Sources of Sorbus aria agg. variation
Bílá, Jana ; Urfus, Tomáš (advisor) ; Krahulec, František (referee)
The main drivers of microevolution in the genus Sorbus are interspecific hybridisation and polyploidy. The fate of new hybrid and polyploid taxa is determined by their mode of reproduction. Especially apomixis could be very advantageous for these new taxa. The S. aria agg. (subg. Aria) plays an important role within the genus since its members are involved in all hybridisation events and thereby is responsible for the substantial part of variation of the genus. Flow cytometry, molecular markers and multivariate morphological analyses were employed to evaluate the processes generating the variability in the S. aria group. Three ploidy levels were detected among species from subg. Aria in the Czech Republic. All of them could be found in the South Moravia, whereas only tetraploids occur in the Bohemia region. Moreover, most of the Czech taxa (5 out of 7) grow also only in the South Moravia which is therefore considered as a centre of diversity of the genus Sorbus in the Czech Republic. Flow cytometry seed screen revealed 7 modes of reproduction among the individuals from S. aria agg. A wide range of sexual and apomictic types of reproduction including reduced and unreduced gametes was detected. All of the diploid individuals are completely sexual. Among polyploid taxa, most of the species are...
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Processes determining the stability of cytotype coexistence in plant populations
Nedomová, Anežka ; Čertner, Martin (advisor) ; Urfus, Tomáš (referee)
Multiplication of nuclear genome is considered one of the most important processes in the plant evolution. Neopolyploids arise in a diploid population by merging of two unreduced gametes or through "triploid bridge". However establishment of a new polyploid in the current population is not easy. Polyploid has to overcome through various mechanisms (like a self-pollination, nonrandom pollination, etc.) "the minority cytotype exclusion" and increase their frequency in the population. Diploids and polyploids differ in ecological demands and competition abilities. There is no correlation between ploidy and wide ecological amplitude or competition abilities. With the current knowledge, we can not determine in which case is the mixed population stable. There is an assumption that the population contains two closely related species simply can not be stable, and therefore all cytotype mixed populations are unstable. Powered by TCPDF (www.tcpdf.org)
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Evoluční mechanismy a vztahy mezi taxony rodu Pilosella
Urfus, Tomáš ; Krahulec, František (advisor) ; Oberprieler, Christoph (referee) ; Rotreklová, Olga (referee)
Several case studies at diffrent levels (population, regional, comparative etc.) were carried out to evaluate the importance of different sources of variation and to follow microevolutionary traits in Pilosella (Asteraceae). The gradient of different spatial levels and comparative studies of closely related taxa group (characterised by partly different type of ongoing microevolution - genus Picris) revealed some common processes while at the same time highlighted the uniqueness of genus Pilosella. Microevolutionary potential was studied at the population level using morphometric approach (hybridization tendencies of highly complex hybrid swarm in Prague - Praha Vysočany). Cytogeography of Pilosella officinarum was then investigated at the regional scale (Central Europe). Tetraploid cytotype was detected almost exclusively in Bohemia region and further to the west whereas pentaploid and hexaploid cytotypes prevailed in Moravia and Slovakia and further to south- east. Cytogeography was followed by morphometric evaluation of three most abundant ploidy levels (4x, 5x and 6x) of P. officinarum combined with the analyses of reproduction mode. Results confirmed the possibility to distinguish the particular cytotypes ...
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Hybridization and microevolutionary relationships among Central European Diphasiastrum species
Dvořáková, Kristýna ; Urfus, Tomáš (advisor) ; Chrtek, Jindřich (referee)
Genus Diphasiastrum Holub is one of the most complicated and biosystematically very little investigated groups within Lycopodiaceae family. There are 6 species recognized in Central European region. Three of them (D. alpinum, D. complanatum, D. tristachyum) are considered basic - parental taxa, and their hybridization probably gave origin to the three adjacent species - intermediates (D. issleri, D. zeilleri, D. oellgaardii). These supposedly hybridogenous taxa often co-ocur with at least one parental species. All the taxa often meet in secondary habitats where they tend to form hybrid swarms (e.g. on ski slopes which represent an ideal biocorridor for meeting the species from alpine zone with the species from lower altitudes). In such places reciprocal crossings between all of the taxa occur, often accompanied by introgression. The degree of hybridization, including the possible introgression, was studied using absolute genome size analyses combined with classical and geometric multivariate morphometrics. Genome size was estimated for 570 plants from 83 localities, mostly from the Czech Republic. Despite the fact that each parental taxa had a specific range of absolute genome sizes, adjacent species formed more or less disconnected continuum. Multivariate statistical methods (PCA, RDA, Loess, PLS)...
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Sources of Sorbus aria agg. variation
Bílá, Jana ; Urfus, Tomáš (advisor) ; Chumová, Zuzana (referee)
Genus Sorbus is a very complex group of vascular plants. Various genetic lineages which can be fixed by apomixis are driven by interspecific hybridisation and polyploidy. Species from S. aria agg. have the highest variation probably due to an extra mechanism - introgressive hybridisation. There are several concepts of the aggregate which are usually based on three main species: S. aria, S. umbellatta and S. graeca. Therefore, new microspecies are derived by genome doubling and hybridisation between the main species. Units of the aggregate are assessed differently as the distinction of taxa is very complicated due to the overlap of the morphological variability. The aggregate itself can be sometimes considered as a category for species of uncertain origin or identification. Four species from S. aria agg. occur in the Czech Republic. In addition, the conclusion offers questions that will be addressed in the master's thesis.
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Evolutionary history of polyploid complex Galium pumilum in Central Europe
Knotek, Adam ; Kolář, Filip (advisor) ; Urfus, Tomáš (referee)
The thesis summarizes current knowledge about the polyploid complex of Galium pummilum agg. in Central Europe. This work should provide a theoretical background for a following diploma thesis. Most species of the aggregate are difficult to be determined due to considerable morphological variability and a complex evolutionary history probably involving recurrent polyploidization and hybridization events. Currently, new molecular methods are changing our opinion on the taxonomical classification within the group. Except for G. pumilum MURRAY, the other species show rather disjunctive distribution and are found on relict habitats. This could be caused by postglacial migration and subsequent area fragmentation. Most of the previous studies focused on Galium were published by Friedrich Ehrendorfer, who since the 50th defined division of the complex on the basis of chorological, karyological and morphological data. With new molecular methods, his hypotheses are now exposed to verification. Galium sudeticum TAUSCH. represents an enigmatic and vulnerable taxon of the Czech flora, that raises various interesting questions from both evolutionary and conservation points of view. It has a remarkable disjunct distribution in the Giant mountains (Krkonoše) and in one serpentine area in western Bohemia...
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Ecological and evolutionary processes in primary contact zone of cytotypes of Knautia arvensis agg.
Hanzl, Martin ; Urfus, Tomáš (referee) ; Kolář, Filip (advisor)
Genome duplication events have played a crucial role in plant evolution. According to recent estimates, nearly all the angiosperms are ancient polyploids. However, establishment of new polyploid lineages within diploid populations seemed to be very unlikely, based on theoretical analyses. Reproductive interactions between the cytotypes (so-called "minority cytotype exclusion") and resource competition might eventually lead to polyploid extinction. On the other hand, the whole variety of factors may compensate both processes under natural conditions (e.g. autogamy, assorative mating, spatial separation of cytotypes). Polyploid establishment in sympatry with diploid progenitor might thus not be as restricted, as previously thought. Subsequent cytotype coexistence may represent a stable equilibrium, or just a transition leading to extinction of one chromosomal race. It is usually almost impossible to discriminate between these alternatives. Polyploid range expansions are usually accompanied by competitive exclusion of diploid cytotype or colonization of new areas and habitats. When two cytological races meet, zones of contact are often formed. Contact zones could be divided into primary and secondary ones. Primary contact zones arise as a consequence of new polyploid emergence within the progenitor's...
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