38,587 research outputs found
Phylogenomic Insights into the Origin of Primary Plastids
No full textAbstract The origin of plastids was a major evolutionary event that paved the way for an astonishing diversification of photosynthetic eukaryotes. Plastids originated by endosymbiosis between a heterotrophic eukaryotic host and cyanobacteria, presumably in a common ancestor of the primary photosynthetic eukaryotes (Archaeplastida). A single origin of primary plastids is well supported by plastid evidence but not by nuclear phylogenomic analyses, which have consistently failed to recover the monophyly of Archaeplastida hosts. Importantly, plastid monophyly and nonmonophyletic hosts could be explained under scenarios of independent or serial eukaryote-to-eukaryote endosymbioses. Here, we assessed the strength of the signal for the monophyly of Archaeplastida hosts in four available phylogenomic data sets. The effect of phylogenetic methodology, data quality, alignment trimming strategy, gene and taxon sampling, and the presence of outlier genes were investigated. Our analyses revealed a lack of support for host monophyly in the shorter individual data sets. However, when analyzed together under rigorous data curation and complex mixture models, the combined nuclear data sets supported the monophyly of primary photosynthetic eukaryotes (Archaeplastida) and recovered a putative association with plastid-lacking Picozoa. This study represents an important step toward better understanding deep eukaryotic evolution and the origin of plastids. [Archaeplastida; Bayesian; chloroplast; maximum likelihood; mixture model; ortholog; outlier loci; paralog; protist.
Author Correction: A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids
No full textA molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids
No full textIn modern oceans, eukaryotic phytoplankton is dominated by lineages with red algal-derived plastids such as diatoms, dinoflagellates, and coccolithophores. Despite the ecological importance of these groups and many others representing a huge diversity of forms and lifestyles, we still lack a comprehensive understanding of their evolution and how they obtained their plastids. New hypotheses have emerged to explain the acquisition of red algal-derived plastids by serial endosymbiosis, but the chronology of these putative independent plastid acquisitions remains untested. Here, we establish a timeframe for the origin of red algal-derived plastids under scenarios of serial endosymbiosis, using Bayesian molecular clock analyses applied on a phylogenomic dataset with broad sampling of eukaryote diversity. We find that the hypotheses of serial endosymbiosis are chronologically possible, as the stem lineages of all red plastid-containing groups overlap in time. This period in the Meso- and Neoproterozoic Eras set the stage for the later expansion to dominance of red algal-derived primary production in the contemporary oceans, which profoundly altered the global geochemical and ecological conditions of the Earth
eine Analyse von Ultrastruktur, Phylogenie und Kospeziation
No full textThe complex mechanisms leading to a tripartite symbiosis involving bacteria,
flagellates, and host termites are not yet fully understood. While the
flagellates are known to play a major role in the degradation of the
cellulosic food of the termites, in most cases, the functions of the diverse
flagellate-associated bacteria are completely obscure. Unambiguous
identification of the mostly uncultivable prokaryotes and eukaryotes is an
important step in understanding the mutual interactions between the two
partners. For this purpose, in the studies described in my thesis,
morphological investigations (light microscopy and electron microscopy) were
combined with molecular phylogenetic analyses (full-cycle-rRNA approach). In
two earlier light microscopy studies, other authors reported contradicting
numbers of devescovinid flagellates occurring in the hindgut of the dry-wood
termite Incisitermes marginipennis. We clearly and unambiguously documented
the presence of only one devescovinid species (Metadevescovina modica)
inhabiting the gut of I. marginipennis using a combination of various light
and electron microscopy techniques and molecular phylogenetic analysis of the
small subunit (SSU) rRNA gene sequences. Moreover, we confirmed the validity
of the genus Metadevescovina, which had long been discussed as being the same
as the genus Devescovina; monophyly of each of the genera was revealed by
molecular phylogenetic analyses. Metadevescovina could not be distinguished
from Devescovina solely by morphological characteristics of the flagellates
themselves, but the two flagellate genera could be differentiated by examining
their bacterial symbionts. The cell surface of Metadevescovina flagellates is
densely colonized with spirochetes, and that of Devescovina flagellates is
densely covered with filamentous bacteria affiliated to the Bacteroidales.
Molecular phylogenetic analyses of Devescovina spp. and their bacterial
symbionts from a wide range of Kalotermitidae revealed that the termites
acquired two bacterial symbionts by two different routes: vertical
transmission and horizontal transmission. The ectosymbionts of Devescovina
spp. form a monophyletic group within the Bacteroidales (“Candidatus
Armantifilum devescovinae”). Congruence analyses of the phylogenetic trees of
Devescovina spp. and “Candidatus Armantifilum devescovinae” documented a
strict cospeciation of the partners, which indicated an obligate symbiosis,
leading to a vertical transmission of the bacteria within their host lineages.
The ‘Endomicrobia’ endosymbionts of Devescovina spp. are most closely related
to endosymbionts of phylogenetically unrelated termite gut flagellates, which
indicated that these symbionts were acquired by horizontal transmission
between different flagellate species present in the same termite gut. In a
further study documented in this thesis, the multiple symbionts of the
flagellate Joenia annectens from the dry-wood termite Kalotermes flavicollis
were identified, localized using a full-cycle-rRNA approach, and
morphologically described at the ultrastructural level. Two populations of J.
annectens could be distinguished not only by their SSU rRNA gene sequences
(0.8% sequence divergence), but also by differences in their assemblages of
bacterial symbionts. Each of the flagellate populations hosted
phylogenetically distinct ectosymbionts from the phylum Bacteroidetes, while a
single phylotype of ‘Endomicrobia’ was consistently associated with only one
of the host phylotypes. However, not all individuals were colonized, once
again corroborating that ‘Endomicrobia’ are not always cospeciating with their
host lineages. The results reported in my thesis provide important information
about the specificity of the symbioses between termite gut flagellates and
their bacterial symbionts. This information is necessary for further studies
of the function of these symbioses. A possible involvement of bacterial
symbionts in the nitrogen metabolism of the host flagellates is discussed.Die komplexen Mechanismen, welche der Dreiersymbiose zwischen Bakterien,
Flagellaten und ihren Wirtstermiten zugrundeliegen, sind bis heute noch
weitgehend unverstanden. Während den Flagellaten eine wesentliche Rolle beim
Abbau der cellulosehaltigen Nahrung der Termiten zugeschrieben wird, sind die
Funktionen der diversen, mit den Flagellaten assoziierten Bakterien in den
meisten Fällen komplett unbekannt. Ein wichtiger Schritt für die Erforschung
der wechselseitigen Beziehungen zwischen den in der Regel nicht kultivierbaren
pro- und eukaryotischen Symbionten stellt deren eindeutige Identifizierung
dar. Dazu wurden in den vorliegenden Studien morphologische Untersuchungen
(Licht- und Elektronenmikroskopie) beider Partner mit molekular-
phylogenetischen Analysen kombiniert (full-cycle-rRNA approach). In zwei
vorangegangenen lichtmikroskopischen Studien anderer Autoren wurde für die
Trockenholztermite Incisitermes marginipennis eine widersprüchliche
Artenanzahl von devescoviniden Flagellaten dokumentiert. Durch den Einsatz
verschiedener licht- und elektronenmikroskopischer Techniken sowie durch die
Analyse der Sequenzvariabilität der Gene der kleinen ribosomalen Untereinheit
(SSU rRNA) konnten wir in der vorliegenden Arbeit eindeutig zeigen, dass I.
marginipennis lediglich eine Art devescovinider Flagellaten (Metadevescovina
modica) im Darm beherbergt. Gleichzeitig konnten wir die Gültigkeit der
Gattung Metadevescovina, welche bis zum heutigen Tag stark umstritten war und
häufig als Synonym zu Devescovina angesehen wurde, bestätigen.
Molekularphylogenetische Analysen zeigten, dass beide Gattungen jeweils eine
separate monophyletische Gruppe bilden. Eine Unterscheidung der beiden
Gattungen an Hand morphologischer Merkmale der Flagellaten selbst war nicht
möglich, konnte jedoch unter Berücksichtigung ihrer bakteriellen Symbionten
erfolgen. Während Flagellaten der Gattung Metadevescovina einen dichten Besatz
von Spirochaeten auf ihrer Oberfläche zeigen, sind Devescovina spp.
vollständig von filamentösen Bakterien bedeckt, welche den Bacteroidales
zugeordnet werden. Molekularphylogenetische Analysen von Devescovina spp. von
verschiedenen Vertretern der Kalotermitidae und ihren bakteriellen Symbionten
ergaben zwei verschiedene Szenarien bezüglich des Erwerbs dieser Symbionten:
Eine vertikale Weitergabe und eine horizontale Weitergabe. Es konnte gezeigt
werden, dass die Ektosymbionten eine monophyletische Gruppe innerhalb der
Bacteroidales bilden („Candidatus Armantifilum devescovinae“).
Kongruenzanalysen der Stammbäume von Devescovina spp. und „Candidatus
Armantifilum devescovinae“ dokumentierten eine strikte Kospeziation der
Partner. Eine obligate Symbiose der beiden Partner, und somit eine vertikale
Weitergabe der Bakterien innerhalb ihrer Wirtsflagellaten, konnte demnach
belegt werden. Der Erwerb von Symbionten durch horizontale Weitergabe von
anderen Wirtsflagellaten wurde dagegen für die im Zytoplasma vorkommenden
‚Endomicrobia‘ dokumentiert. Hier waren die nächsten Verwandten der mit den
Devescovina spp. assoziierten ‚Endomicrobia‘ Endosymbionten von phylogenetisch
nicht verwandten Termitenflagellaten. In einer weiteren Studie dieser Arbeit
wurden die multiplen Symbionten des Flagellaten Joenia annectens aus der
Trockenholztermite Kalotermes flavicollis identifiziert und lokalisiert (full-
cycle-rRNA approach). Ultrastrukturelle Untersuchungen ermöglichten eine
morphologische Beschreibung der gefundenen Phylotypen. Basierend auf den
Assoziationen mit phylogenetisch verschiedenen Symbionten konnten zwei
Populationen von J. annectens unterschieden werden. Gestützt wurde das
Ergebnis durch die Analyse der SSU rRNA Gensequenzen von J. annectens (0,8%
Sequenzunterschied zwischen beiden Populationen). Beide
Flagellatenpopulationen waren jeweils mit eigenen Ektosymbionten des Phylums
Bacteroidetes assoziiert. Dahingegen beherbergte nur eine der beiden
Populationen von J. annectens einen Vertreter der ‚Endomicrobia‘ im
Zytoplasma. Das Fehlen von ‚Endomicrobia‘-Symbionten bei vielen Flagellaten
der gleichen Population zeigt ein weiteres Beispiel dafür, dass diese
Symbionten nicht immer mit ihren Wirtsflagellaten kospeziieren. Die Ergebnisse
meiner Arbeit haben wichtige Erkenntnisse zur Spezifität der Symbiosen
zwischen Termitenflagellaten und ihrer bakteriellen Symbionten gebracht. Sie
stellen somit eine Grundvoraussetzung für die anstehende Erforschung der
funktionellen Aspekte dieser Symbiosen dar. Eine Beteiligung der bakteriellen
Symbionten am Stickstoffstoffwechsel der Flagellaten wird diskutiert
Early Diversification of Membrane Intrinsic Proteins (MIPs) in Eukaryotes
No full textAbstract Membrane intrinsic proteins (MIPs), including aquaporins (AQPs) and aquaglyceroporins (GLPs), form an ancient family of transporters for water and small solutes across biological membranes. The evolutionary history and functions of MIPs have been extensively studied in vertebrates and land plants, but their widespread presence across the eukaryotic tree of life suggests both a more complex evolutionary history and a broader set of functions than previously thought. That said, the early evolution of MIPs remains obscure. The presence of one GLP and four AQP clades across both bacteria and archaea suggests that the first eukaryotes could have possessed up to five MIPs. Here, we report on a previously unknown richness in MIP diversity across all major eukaryotic lineages, including unicellular eukaryotes, which make up the bulk of eukaryotic diversity. Three MIP clades have likely deep evolutionary origins, dating back to the last eukaryotic common ancestor (LECA), and support the presence of a complex MIP repertoire in early eukaryotes. Overall, our findings highlight the growing complexity of the reconstructed LECA genome: the dynamic evolutionary history of MIPs was set in motion when eukaryotes were in their infancy followed by radiative bursts across all main eukaryotic lineages.Open-Access-Publikationsfonds 202
Letter from A. F. Potter to John H. Page
No full textLetter from A. F. Potter to John H. Page referring his request to build a railway to the District Forester at Albuquerque, New Mexico
Polly H. Carder Collection on George F. Root
No full textGeorge Frederick Root (1820-1895) was an American songwriter and music educator. He is perhaps best known for his song "The Battle Cry of Freedom," which was written and rose to popularity during the U.S. Civil War. The Polly H. Carder Collection on George F. Root contains original published scores and songbooks from the period 1852-1907 and photocopied scores collected by Polly H. Carder, author of the book George F. Root, Civil War Songwriter: A Biography. The collection also contains a short article, "The Last Days of George F. Root," written by Root's daughter, Clara Louise Burnham
O poder constituinte em Hannah Arendt e Jürgen Habermas
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas, Programa de Pós-Graduação em Filosofia, Florianópolis, 2014.O trabalho analisa o tema do poder constituinte na perspectiva de Hannah Arendt e de Jürgen Habermas. A hipótese é de que Habermas, ao justificar a institucionalização do princípio do discurso, estaria, com isso, propondo a formalização do poder constituinte. Afinal, a prática constituinte, diz ele, supõe a institucionalização de formas de comunicação capazes de proporcionar a formação discursiva de uma vontade política racional. Isso, porém, até onde alcança nossa compreensão, não ocorre em H. Arendt, pois a mesma defende a tese de um poder constituinte calcado na geração espontânea do poder e sustentado pela promessa. Estima-se que Habermas queira avaliar a possibilidade de trazer o potencial inovador da revolução para o âmbito do Estado democrático de direito. Nesse caso, precisa ir além tanto da concepção que limita o poder constituinte, trazendo-o para dentro do sistema normativo estatal, visando à sua operacionalização através de instituições do próprio Estado, como da concepção que o define como uma manifestação política que não integra o próprio direito, caracterizando-se, portanto, como uma força social que cria o direito e, em seguida, recolhe-se para que a organização normativa da sociedade se realize no âmbito estatal. Habermas, nesse aspecto, parece seguir na direção intermediária, ou seja, na direção daqueles que acreditam que o poder constituinte pode ocupar uma dupla posição, definindo-se tanto como manifestação política que integra o ato revolucionário da fundação, quanto como força social quepermanece implícita, como tensão, no cotidiano do legislativo e do judiciário. A tese, portanto, é de que a expressão remains implicit, utilizada por Habermas em Direito e democracia, parece sugerir que o poder constituinte se mantém operante mesmo depois da constituição do Estado democrático de direito, ou melhor, que poder constituinte revolucionário continua a obrar no trabalho diário do legislativo e do judiciário. Tal tese encontra, ou parece encontrar, sustentação inclusive em Carl Schmitt quando afirma, no § 8 da sua clássica obra Verfassungslehre (Teoria da Constituição), que quanto a permanência, resta ao o poder constituinte sempre a possibilidade de seguir existindo encontrando-se ao mesmo tempo acima de toda Constituição, que é derivada dele, de toda a determinação legal-constitucional, válida no marco dessa Constituição. Nessas condições, acredita-se que a natureza do poder constituinte, postulada por Schmitt, sugere, no que tange à ideia de permanência, certa convergência com aquela encontrada em Habermas, parecendo referir-se não somente a um ato ou momento, mas a um procedimento que abarca12vários momentos institucionais, vários agentes e várias forças intelectuais em disputa.Abstract : This study analyzes the theme of constituent power from Hannah Arendt's and Jürgen Habermas' perspectives. The hypothesis is that when Habermas justifies the institutionalization of the discourse principle, he would be proposing the formalization of constituent power. After all, he asserts that the constituent practice presupposes the institutionalization of modes of communication which is able to promote the discursive formation of a rational political will. However, as far as we are concerned, this does not occur in H. Arendt, as she defends the view that constituent power is based on spontaneous generation of power and sustained by the promise. It is expected that Habermas wants to assess the possibility of joining innovative potential to the scope of the democratic State governed by the rule of law. In this case, it is necessary to go beyond the view that limits constituent power, bringing it to the normative state system which aims at the operationalization through the institutions of the State itself, such as the concept which defines it as a political demonstration that does not integrate its own law, thus characterizing it as a social force that creates the law and, then, is collected in order for the normative organization of the society to occur in a state level. In this aspect, Habermas seems to follow the intermediate direction, that is, the direction of those who believe that constituent power may occupy dual position, thus defining itself as political demonstration which integrates the revolutionary act of the foundation, as a social force which remains implicit, as tension, in the legislative and judiciary daily routine. Therefore, the view is that the expression remains implicit, used by Habermas in Law and democracy, seems to suggest that constituent power continues to operate even after the constitution of the democratic State, based on the rule of law. In other words, the revolutionary constituent power continues to work on the legislative and judiciary daily tasks. Such view encounters or seems to encounter support, including in Carl Schmitt, when he asserts in paragraph 8 of his classic work Verfassungslehre (Constitution Theory) that, in relation to permanence, it is left to the constituent power Always the possibility to continue existing, at the same time finding above all Constitution, which derives from it, of all constitutional and legal determination, valid in this Constitution landmark. In these conditions, it is believed that the nature of constituent power, postulated by Schmitt, suggests, regarding the idea of permanence, some convergence with that one found in Habermas, which seems to refer not only to an act or a moment, but to a procedure which14includes various institutional moments, several agents and intellectual forces in dispute
Predatory colponemids are the sister group to all other alveolates
No full textAlveolates are a major supergroup of eukaryotes encompassing more than ten thousand free-living and parasitic species, including medically, ecologically, and economically important apicomplexans, dinoflagellates, and ciliates. These three groups are among the most widespread eukaryotes on Earth, and their environmental success can be linked to unique innovations that emerged early in each group. Understanding the emergence of these well-studied and diverse groups and their innovations has relied heavily on the discovery and characterization of early-branching relatives, which allow ancestral states to be inferred with much greater confidence. Here we report the phylogenomic analyses of 313 eukaryote protein-coding genes from transcriptomes of three members of one such group, the colponemids (Colponemidia), which support their monophyly and position as the sister lineage to all other known alveolates. Colponemid-related sequences from environmental surveys and our microscopical observations show that colponemids are not common in nature, but they are diverse and widespread in freshwater habitats around the world. Studied colponemids possess two types of extrusive organelles (trichocysts or toxicysts) for active hunting of other unicellular eukaryotes and potentially play an important role in microbial food webs. Colponemids have generally plesiomorphic morphology and illustrate the ancestral state of Alveolata. We further discuss their importance in understanding the evolution of alveolates and the origin of myzocytosis and plastids
Few H copies in F-saturated graphs
No full text© 2019 Wiley Periodicals, Inc. A graph is F-saturated if it is F-free but the addition of any edge creates a copy of F. In this paper we study the function sat(n,H,F) which is the minimum number of copies of H that an F-saturated graph on n vertices may contain. This function is a natural saturation analogue of Alon and Shikhelman's generalized Turan problem, and letting H=K2 recovers the well-studied saturation function. We provide a first investigation into this general function focusing on the cases where the host graph is either Ks or Ck-saturated. Some representative interesting behavior is: For any natural number m, there are graphs H and F such that sat(n,H,F)=Theta(nm). For many pairs k and l, we show sat(n,Cl,Ck)=0. In particular, we prove that there exists a triangle-free Ck-saturated graph on n vertices for any k>4 and large enough n. sat(n,K3,K4)=n-2, sat(n,C4,K4)similar to n22, and sat(n,C6,K5)similar to n3. (a)(b)(c) We discuss several intriguing problems that remain unsolved11Nsci
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