|
Concept of species in bears (Ursidae): practical, historical, and theoretical viewpoint
Wagner, Jan ; Fejfar, Oldřich (advisor) ; Sabol, Martin (referee) ; Musil, Rudolf (referee)
The present thesis surveys topic of taxonomic diversity and phylogeny of bears (Mammalia, Ursidae) and aspects of its contextual setting under effects of changing conceptual and methodological viewpoints. This problem is studied from several perspectives. The historical perspective is represented by a critical overview of the history of specific and infraspecific classification of bears with special respect to mutual influences of this classification and theoretical concepts of species accepted in particular periods. The perspective of material approach is exemplified by a material-based study of taxonomical and phyletic status of selected Pliocene to Middle Pleistocene ursine taxa. Along with deconstruction of some traditional hypotheses this produced a model explaining species diversification in ursine bears and its discussion in terms of factual relevance of included background concepts. In the pre-evolutionary period the bear species were usually understood broadly, as incipient immanent entities, yet exhibiting obvious certain infraspecific variability. This was established using definitions of varieties (mostly not identifiable with present subspecies or infraspecific taxa) considered as unstable modes of particular species. Although, in the post-Darwinian period, the concept and taxonomic...
|
|
Speciation and fractionation analysis of metals in agricultural soils
Lepař, Petr ; Mládková, Zuzana (referee) ; Diviš, Pavel (advisor)
This bachelor thesis deals with the procedures and analytical techniques associated with speciation analysis and fractionation of metals in agricultural soils. The first part defines the basic concepts related to speciation, fractionation, soils and elements contained within it. The following chapters describe procedures of samples withdrawal and its adjustment including a description of some methods used for the purpose of extraction, fractionation and speciation analysis. The last chapter is devoted to listing of some separation techniques and instrumental methods used for the purposes of speciation and fractionation.
|
|
Methods for Elemental Speciation of Arsenic Compounds.
Navrátilová, Jana ; Jarošová, Alžběta (referee) ; Golian,, Jozef (referee) ; Šimko, Peter (advisor)
Speciační analýza arsenu v různých matricích s využitím HPLC/ICPMS byla předmětem této práce. Toxicita arsenu závisí na oxidačním stavu a formě, ve které je přítomen. Znalost zastoupení specií arsenu je nutná k hodnocení toxicity a biodostupnosti. Obecně, anorganické specie jsou více toxické než organické. V práci byla studována degradace arsenocukrů v mořských řasách za simulovaných přirodních podmínek. Původní arsenocukry byly transformovány na arseničnan a kyselinu dimethylarseničnou. Arsen vstupuje do rostlin z půdy a vody a následně může vstoupit do potravního řetězce. S ohledem na tuto skutečnost byla speciační analýza provedena u vybraných vzorcích rýže, zakoupených v české obchodní síti. Stanovený celkový obsah arsenu se pohyboval v rozmezí 36.06 µg/kg - 218.11 µg/kg a hlavními speciemi byla kyselina dimethylarseničná a anorganický arsen (54-78%). Mořské ryby a tuky obsahují významnou část arsenu ve formě zvané arsenolipidy. Část práce byla zaměřena na analýzu arsenolipidů u máslové ryby (Lepidocybium flavobrunnrum) s celkovým obsahem arsenu 1.8 mg/kg a 22% celkového arsenu bylo vyextrahováno pomocí hexanu, což potvrzuje lipofilni charakter těchto sloučenin. Hlavní specií stanovenou ve vodném extraktu byl arsenobetain, představující 89%.
|
| |
|
Monitoring of arsenic forms in foodstuffs
Harkabusová, Veronika ; Hrstka, Miroslav (referee) ; Vitoulová, Eva (advisor)
The diploma thesis is dealing with monitoring of arsenic in foodstuffs. The aim of this thesis is the determination of arsenic in samples of fish and rice and the study of forms, in which arsenic occurs, using speciation analysis. Arsenic is known as a toxic element, but its measure of toxicity depends on the chemical form it occurs in. Arsenic is present in the environment naturally or it gets in the environment by human activities. Complete characterization of arsenic compounds is necessary to understand intake, accumulation, transport, detoxification and activation of this element in the natural environment and living systems. The field of arsenic speciation analysis has grown rapidly in recent years, because determination of the total element content is not sufficient in the case of arsenic. Speciation method was done using separation by high performance liquid chromatography and detection by atomic fluorescence spectrometry with hydride generation. Extractable arsenic was present in the form of nontoxic arsenobetaine in all analysed samples of fish. In samples of rice there was confirmed the presence of toxic inorganic species of arsenic, esspecially As (III), but their concentration was at low level.
|
|
Evolutionary role of triploids in diploid-tetraploid populations of Arabidopsis arenosa and Cardamine amara
Voltrová, Alena ; Kolář, Filip (advisor) ; Chrtek, Jindřich (referee)
This thesis addresses the evolutionary potential of interploidy gene flow mediated by triploid individuals of two mixed-ploidy species, Arabidopsis arenosa and Cardamine amara, both from Brassicaceae family. In natural secondary contact zones formed by diploid and autotetraploid cytotypes, triploids of both species are rarely occurring, being represented only by 0.2 % and 2.5 % of individuals in A. arenosa and C. amara, respectively. Yet their role in gene flow between parental diploid-tetraploid populations remain unclear although genetic data confirmed significant traces of interploidy introgression. By crossing experiments of both species of triploids with their parental ploidies, I addressed the potential of triploids as mediators of gene flow. Specifically, the fertility of triploids and their ability to backcross with their diploid and tetraploid parents. Successful crosses involving triploids both as mothers and fathers demonstrated triploid's ability to form viable male and female gametes. A significant fraction of seeds produced out of these crossings was able to germinate and survive. The progeny was largely aneuploid, but both basic euploids were observed, demonstrating a clear pathway how triploids can backcross back towards diploid and tetraploid ploidies. In C. amara, field...
|
|
Karyotype evolution in estrildid finches of the genus Lonchura
Janáková, Šárka ; Reifová, Radka (advisor) ; Augstenová, Barbora (referee)
The karyotype, the set of all chromosomes in a cell, is an important characteristics of individual species of both animals and plants. The karyotype of birds is typically stable in terms of the number of chromosomes and their size, and rearrangements between different chromosomes are rare. The changes that occur between the karyotypes of avian species are more often intrachromosomal, such as inversions or duplications and deletions. It is still unclear how often such changes occur between closely related species and whether they can contribute to speciation. This work aims to compare the karyotypes of a total of five closely related species of songbirds of the genus Lonchura (munias and mannikins). Comparing chromosomal changes in such recently diverged species allows us to observe changes that might contribute to speciation. The study is based on karyotype analysis by immunofluorescence staining of synapsed pachytene chromosomes and subsequent identification and comparison of chromosome types. This method allows determination of the changes that are manifested by pericentric inversions where the position of the centromere is changed. The results confirm the general idea of avian karyotypes as very conservative in terms of chromosome number and their sizes. However, in some chromosomes we observed...
|
|
Speciation mechanisms and the role of reinforcement in mammals
Horký, Jakub ; Hulva, Pavel (advisor) ; Reifová, Radka (referee)
Speciation, the process of the formation of new species, comprises a diverse range of microevolutionary mechanisms acting in unison, which lead to the gradual formation of reproductive barriers between populations. The study of speciation has significantly progressed since its origins around the midpoint of the nineteenth century, owing to progressively improving analytical methods and the data said methods obtained, allowing us to observe previously invisible patterns and form new hypotheses on their basis. From traditional to modern research, this review's goal is to describe the contemporary understanding of speciation's concepts and mechanisms, focusing on those which are most relevant to mammals. Modern understanding of spatial contexts, prezygotic and postzygotic isolating mechanisms, and character displacement, including a type of reproductive character displacement dubbed reinforcement, are discussed. Significant emphasis is placed on the topics of maladaptive and adaptive hybridization, which, together with reinforcement and development of new genomic methods, has this review identified as the current frontier of speciation research. Keywords: reproductive isolating mechanisms, microevolution, character displacement, hybridization, reinforcement, speciation
|
|
triggers of asexual reproduction: on the crosslink between hybridization, asexuality, polyploidy and speciation on example of Cobitidae loaches
Marta, Anatolie ; Janko, Karel (advisor) ; Arai, Katsutoshi (referee) ; Trachtulec, Zdeněk (referee)
(in English) Sexual reproduction is considered a nearly universal feature of all eukaryotic organisms and has been hypothesized to be their ancestral state. Sexual reproduction is mainly represented by meiotic division, recombination, production of haploid gametes and fertilization. Although molecular and cytological mechanisms underlying meiosis are highly conservative they may be disrupted in numerous ways leading to the emergence of so-called asexual lineages. The proximate origins of asexuality may differ for particular taxa. In vertebrates, asexuality frequently is triggered by interspecific hybridization. Nowadays "classical" theories predict that asexuals should not be able to persist on a long-term evolutionary scale. However, the hybrid lineages have to overcome short-term disadvantages, such as postzygotic barriers ranging from complete hybrid sterility to altered meiosis resulting in asexual reproduction and even ploidy elevation. Despite that hybrid sterility is one of the most common outcomes of interspecific hybridization, however various lineages found their ways to alleviate these problems and produce viable clonal gametes. The knowledge about proximate mechanisms of unreduced gamete formation in asexual lineages is very limited as many studies were restricted due to methodological...
|
|
Mechanisms of reproductive isolation between two hybridizing passerine species, the common nightingale and the thrush nightingale
Poignet, Manon ; Reifová, Radka (advisor) ; Choleva, Lukáš (referee) ; Kratochvíl, Lukáš (referee)
iv - ABSTRACT (in English) - A key step in the origin of new species is the evolution of the reproductive isolation mechanisms separating the gene pools of newly emerging species. Despite a growing number of studies, we still know very little about the molecular, physiological and genetic mechanisms underlying reproductive isolation. Hybrid zones represent useful examples of ongoing species differentiation and can provide information about the nature of reproductive isolation separating the species and mechanisms facilitating or limiting the hybridization. Using two naturally hybridizing passerine species, the common nightingale (Luscinia megarhynchos) and the thrush nightingale (L. luscinia), we evaluated several mechanisms of reproductive isolation at the chromosomal, phenotypic, and genetic levels, with a focus on postmating prezygotic (PMPZ) and postzygotic isolation mechanisms. These nightingale species diverged ~1.8 Mya and currently hybridize in a secondary contact zone running across Central and Eastern Europe. First, we analysed the genetic composition of the secondary contact zone, demonstrating that parental forms are predominant in the hybrid zone, with few F1 hybrids (3.4%), early backcross hybrids (3.1%) and the absence of F2 hybrids. This suggests strong but incomplete reproductive isolation....
|