Major progress has been made during the last twenty years towards a better understanding of the evolution of angiosperms. Early molecular-phylogenetic analyses revealed three major groups, with eudicots as well as monocots being monophyletic, arisen from a paraphyletic group of dicotyledonous angiosperms (= basal angiosperms). Consistently, numerous phylogenetic studies based on sequence data have recovered the eudicot-clade and increased confidence in its existence. Furthermore this clade, which contains about 75% of angiosperm species diversity, is characterized by the possession of tricolpate and tricolpate-derived pollen and has thus also been called the tricolpate clade. Based on molecular-phylogenetic investigations several lineages, such as Ranunculales, Proteales (= Proteaceae, Nelumbonaceae, Platanaceae), Sabiaceae, Buxaceae plus Didymelaceae, and Trochodendraceae plus Tetracentraceae were shown as belonging to a early-diverging grade (early-diverging or “basal” eudicots), while larger groups like asterids, Caryophyllales, rosids, Santalales, and Saxifragales were identified as being members of a highly supported core clade, the so called “core eudicots”. Nevertheless, phylogenetic relationships among several lineages of the eudicots remained difficult to resolve. This thesis is mainly concentrated on fully resolving the branching order among the different clades of the early-diverging eudicots as well as on clarifying phylogenetic and systematic conditions within several lineages, based on phylogenetic reconstructions using sequence data of rapidly-evolving and non-coding molecular regions, such as spacers and introns. Commonly, fast-evolving and non-coding DNA was used to infer relationships among species and genera, as practised in chapter 3, due to the assumption of being inapplicable caused by putative high levels of homoplasy through multiple substitutions and frequent microstructural changes resulting in non-alignability. However, during the last few years numerous molecular-phylogenetic studies were able to present well resolved angiosperm trees on the basis of rapidly-evolving and non-coding regions from the large single copy region of the chloroplast genome comparable to multi-gene analyses concerning topology and statistical support. Mutational dynamics in spacers and introns was revealed to follow complex patterns related to structural constraints like the introns secondary structure. Therefore extreme sequence variability was always confirmed to mutational hotspots that could be excluded from calculations. Moreover it became clear that combining these non-coding regions with the fast-evolving matK gene can lead to further resolved and statistical supported trees.
Chapter 1 deals with the placement of Sabiales inside the early-diverging eudicot grade, while investigating mutational dynamics as well as the utility of different kinds of non-coding and rapidly-evolving DNA within deep-level phylogenetics. It was done by analyzing a combination of nine regions from the large single copy region of the chloroplast genome, including spacers, the sole group I intron, three group II introns and the coding matK for a sampling of 56 taxa. The presented topology is in mainly congruence with the hypothesis on phylogenetic relationships among early-branching eudicots that was gained through the application of a reduced set of five non-coding and fast-evolving molecular markers, including the plastid petD (petB-petD spacer, petD group II intron) plus the trnL-F (trnL group I intron, trnL-F spacer) region and the matK gene. It showed a grade of Ranunculales, Sabiales, Proteales, Trochodendrales and Buxales. The current study differs in showing Sabiales as sister to Proteales in all phylogenetic analyses, in contrast to a second-branching inside early-diverging eudicots and a Bayesian tree displaying Sabiales branching after Proteales. All three hypotheses were tested concerning their likelihood. None of them was shown as being significantly declinable. Thus, albeit the number of characters and informative sites was doubled in comparision to the five-region investigation, the exact position of the Sabiales remained to be resolved with confidence. However, the advanced analyses of the phylogenetic structure of the three different non-coding partitions in comparison to coding genes resulted in the recognition of a significantly higher mean phylogenetic signal per informative character within spacers and introns than in the frequently applied slowly-evolving rbcL gene. The fast-evolving and well performing matK gene is shown to be nested within the non-coding partitions in this respect. Interestingly, the least constrained spacers displayed considerably less phylogenetic structure than both, the group I intron and the group II introns. Molecular evolution is again shown to follow certain patterns in angiosperms, as indicated by the occurrence of mutational hotspots and their connection to structural and functional constraints. This is especially shown for the group II introns studied where highly dynamic sequence parts were rather found in loops than stems.
The aim of chapter 2 was to present a comprehensive reconstruction of the phylogenetic relationships inside the order of Ranunculales, the first-branching clade of the early-diverging eudicots, with an emphasis on the evolution of growth forms within the group. Currently, the order comprises seven families (Ranunculaceae, Berberidaceae, Menispermaceae, Lardizabalaceae, Circaeasteraceae – not included due to lacking plant material, Eupteleaceae, Papaveraceae) containing predominantly herbaceous groups as well as trees and lianescent/shrubby forms. A surprising result that emerged due to the increased use of molecular data within systematics during the last twenty years is the inclusion of the woody Eupteleaceae into Ranunculales. Because of its adaptation to wind pollination it was previously placed next to Hamamelididea. Although phylogenetic hypotheses agreed in the exclusion of Eupteleaceae and the predominantly herbaceous Papaveraceae from a core clade the branching order within early-diverging Ranunculales remained a question to be answered. Thus phylogenetic reconstructions based on molecular data of 50 taxa (including outgroup), applying the well-performing non-coding petD and trnL-F as well as the trnK/matK-psbA region including the coding matK, were carried out. The comprehensive sampling resulted in fully resolved and highly supported phylogenies in both, maximum parsimony and model based approaches, with family relations within the core clade being identical and Euptelea appearing as first branching lineage. However, the relationships among the early-diverging Ranunculales could not be resolved with confidence, a result in line with the finding made in chapter 1. The topology was further resolved as Lardizabalaceae being sister to the remaining members of the order, followed by Menispermaceae, Berberidaceae and Ranunculaceae, the latter sharing a sistergroup relationship. Inside the mainly lianescent Lardizabalaceae the shrubby Decaisnea was clearly depicted as first-branching. The systematic controversial Glaucidium and Hydrastis are shown to be early-diverging members of the Ranunculaceae.
A central goal of chapter 3 was to test phylogenetic relationships among the members of the ranunculaceous tribe Anemoneae. Currently it consists of the subtribes Anemoninae including Anemone, Hepatica, Pulsatilla and Knowltonia, and Clematidinae, consisting of Archiclematis, Clematis and Naravelia. Furthermore the position and taxonomic rank of several lineages inside the subtribe Anemoninae were examined. Since recent comprehensive molecular-phylogenetic investigations have been carried out for the members of Clematidinae or Anemoninae, 63 species representing all major lineages of the two subtribes were included into analyses. Calculations were carried out on the basis of molecular data of the nuclear ribosomal ITS1&2 and the plastid atpB-rbcL intergenic spacer region. Phylogenetic reconstructions resulted in the recognition of two distinct clades within the tribe, thus corroborating the formation of the two subtribes. Within the subtribe Anemoninae the traditional genera Knowltonia, Pulsatilla and Hepatica are confidently shown to be nested within the genus Anemone. The preliminary classification of the genus, currently consisting of the two subgenera Anemone and Anemonidium, is complemented by the subgenus Hepatica.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:25195 |
| Date | 16 December 2009 |
| Creators | Barniske, Anna-Magdalena |
| Contributors | Neinhuis, Christoph, Quandt, Dietmar, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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