Voici les éléments 1 - 10 sur 42
  • Publication
    Accès libre
    Evolutionary diversification in the hyper-diverse montane forests of the tropical Andes: radiation of Macrocarpaea (Gentianaceae) and the possible role of range expansion
    (2021-11-19) ; ;
    Hughes, Colin
    ;
    The humid mid-elevation montane forests (MMF) of the tropical Andes harbour high levels of plant species diversity, contributing to the exceptional overall diversity of the tropical Andean biodiversity hotspot. However, little is known about the diversification dynamics of MMF plant lineages compared to lineages in other Andean biomes. Here, we use Macrocarpaea (Gentianaceae) to investigate patterns of plant diversification in the MMF, using molecular dating with fossils and secondary calibration (from a family-wide phylogenetic analysis of Gentianaceae). We sequenced 76 of 118 recognized Macrocarpaea spp. for six markers to reconstruct a time-calibrated phylogenetic tree and infer the historical biogeography of Macrocarpaea using maximum-likelihood methods implemented in BioGeoBEARS, estimating diversification rates through time and among lineages with BAMM. We document a rapid radiation of Macrocarpaea in Andean MMF coinciding with rapid colonization and range expansion across the entire distribution of the genus in the Andes starting 7.2 Mya. Our results support allopatric founder-event speciation as the dominant process contributing to geographical phylogenetic structure across the genus. We propose that establishment of the MMF in the late Miocene, when the Andes attained critical elevation to modify regional climates, provided large new areas of suitable habitat for Macrocarpaea to quickly colonize and expand through repeated founder-events. We suggest that this wave of colonization and range expansion triggered rapid diversification, and, as the MMF became progressively occupied, the diversification rate slowed. Our study also supports the idea that MMF plant radiations are older and more slowly evolving than the quickly evolving lineages in the recent Andean high-elevation grasslands.
  • Publication
    Accès libre
    Evolution of moonwort ferns ("Botrychium", Ophioglossaceae) on local to global scales
    (2017)
    Dauphin, Benjamin
    ;
    Les plantes ont depuis longtemps fasciné les biologistes par leur capacité à former des espèces cryptiques, des hybrides entre des espèces distinctes, de grandes tailles de génomes stables, et une large variété de systèmes reproducteurs parmi les taxons qui ont conduit à l’actuelle biodiversité des plantes. Il y a plus de 450 millions d’années, les plantes vasculaires ont émergé et colonisé la terre. Rapidement, elles se sont dispersées pour explorer de nouveaux habitats et se sont diversifiées dans des environnements favorables pour former plus de 300 000 espèces vivantes. Une meilleure compréhension des forces évolutives passées qui ont mené aux morphologies, aux écologies, et aux diversités génétiques actuelles des plantes est essentielle pour prédire leur évolution, particulièrement dans le contexte des changements globaux. Ainsi, les objectifs principaux de cette thèse consistaient à étudier les relations phylogénétiques parmi les taxons de Botrychium et comment l’allopolyploïdie et l’alternance des systèmes reproducteurs ont mené à la spéciation de ces espèces.
    Dans un cadre multidisciplinaire, nous avons combiné la phylogénétique avec la génétique des populations et la cytométrie en flux pour produire des données cellulaires et moléculaires pertinentes pour l’exploration des mécanismes biologiques clefs prenant place à des échelles locales ou globales. Etant les fondements de notre projet, nous avons reconstruit la phylogénie chloroplastique du genre Botrychium basée sur un échantillonnage mondiale pour examiner les relations de parentés parmi les taxons diploïdes et les origines maternelles des allopolyploïdes. Dans une seconde étape, nous avons estimé les tailles de génome des Botrychium diploïdes et polyploïdes pour comparer les variations du contenu en ADN après l’allopolyploïdisation et entre les niveaux de ploïdie. Ensuite, nous avons utilisé le séquençage PacBio pour inférer une phylogénie moléculaire dans le but de révéler l’histoire évolutive des deux, les lignées maternelles et paternelles des allopolyploïdes, et d’établir l’échelle temporelle de leur héritage bi-parentale basée sur les estimations des temps de divergence. Travaillant à une échelle régionale et locale, nous avons génotypé des populations de B. lunaria des alpes en utilisant des variants enzymatiques co-dominants et des données de séquençage ddRAD pour caractériser le mode prédominant de reproduction ainsi que leur histoire démographique durant le dernier maximum glaciaire.
    Nous avons trouvé des résultats inattendus et des découvertes majeures pour la compréhension de la biologie des plantes vasculaires précoces. Pour la diversité spécifique elle-même, nous avons identifié treize nouveaux taxons potentiels et caractérisé la diversité exceptionnelle d’haplotypes survenant dans le complexe d’espèce Lunaria. De plus, nous avons présenté des évidences pour l’origine multiple de plusieurs taxons allopolyploïdes et révélé des cas incontestables de dipersion intercontinentale d’amérique du nord vers l’europe et l’asie. Avec la cytométrie en flux, nous avons rapporté un nouveau taxa hexploïde chez Botrychium et avons décrit différentes tailles de génome entre espèces diploïdes des deux clades majeurs, Lanceolatum et Lunaria. Par ailleurs, nos résultats ont supporté le scénario de stabilité des tailles de génome après l’allopolyploidization, rejetant ainsi l’hypothèse de la réduction des tailles de génome largement acceptée chez les angiospermes. Le résultat le plus frappant dans nos investigations phylogénétiques est probablement la récurrence de l'allopolyploïdie dans ce genre et les contributions asymétriques des donneurs parentaux dans la formation des taxons allopolyploïdes. De plus, nos estimations du temps de divergence ont révélé la spéciation récente et rapide par allopolyploïdie au cours des deux derniers millions d'années, ce qui constitue un premier cas de radiation dans l'ancienne lignée des Ophioglossaceae. Pour notre étude sur la génétique des populations, nous avons trouvé une diversité génétique sans précédent dans les populations de B. lunaria avec un grand nombre d'hétérozygotes qui soutient la prédominance pour la fécondation croisée. Ainsi, nous avons présenté les capacités de dispersion et de diversification des espèces de Botrychium afin de mieux comprendre le système d'accouplement des plantes vasculaires ancestrales. En tant qu'élément clef de ce modèle de spéciation, nous avons trouvé une signature génétique indicative d'un refuge pour B. lunaria dans les alpes centrales lors du dernier maximum glaciaire, lequel a abrité des individus ayant une richesse allélique élevée, qui se sont ensuite dispersés durant la déglaciation tout en maintenant la fécondation croisée.
    Indéniablement, le genre Botrychium offre une occasion unique d'aborder le rôle de l'allopolyploïdie et l'importance de l'alternance des systèmes d'accouplement dans la spéciation des plantes. Ce travail est destiné à être le point de départ pour d'autres études en biologie évolutive, lesquelles permettront peut-être de mieux comprendre le cycle de vie de ces espèces de fougères énigmatiques., Plants have long fascinated biologists by their ability to form cryptic species, hybrids between distinct species, large and stable genome sizes, and a wide variety of mating systems among taxa that have driven to the current plant biodiversity. More than 450 million year ago, vascular plants emerged and colonized the land. Rapidly, they dispersed to explore new habitats and diversified in suitable environments to form over 300,000 extant species. A better understanding of past evolutionary forces that led to the current plant morphologies, ecologies, and genetic diversity is critical for predicting their evolution, especially with the global changes ongoing. In this context, the main goals of this thesis were to investigate the phylogenetic relationships among the early divergent Botrychium taxa and how allopolyploidy and the alternation of mating systems have led to the speciation of these species.
    In a multidisciplinary framework, we combined phylogenetics with population genetics and flow cytometry to provide relevant cellular and molecular data for exploring key biological mechanisms taking place at local or global scale. As the backbone of our project, we reconstructed the plastid phylogeny of the genus Botrychium based on a worldwide sampling to investigate relationships among diploid taxa and the maternal origins of allopolyploids. As a second step, we estimated the genome sizes of Botrychium diploids and polyploids to study fluctuations of DNA amounts after allopolyploidization and between ploidy levels. Then, we applied PacBio sequencing to infer a nuclear phylogeny for revealing the evolutionary history for both, the maternal and the paternal lineages of allopolyploids, and drawing the timescale of their bi-parental inheritance based on divergence time estimates. Focusing at a local and regional scale, we genotyped B. lunaria populations in Alps using co-dominant allozymes and ddRADseq data to identify the predominant mode of reproduction as well as its demographic history during the last glacial maximum.
    We found unexpected results and major discoveries for the understanding of the biology of early vascular plants. For the species diversity itself, we identified thirteen possibly new taxa and characterized the exceptional haplotype diversity occurring in the Lunaria complex. Also, we presented evidence for multiple origins of several polyploid taxa and highlighted incontestable cases of inter-continental dispersal from North America to Europe and Asia. With flow cytometry, we reported a new hexaploid in Botrychium and described different genome sizes between diploid species of the two major clades Lanceolatum and Lunaria. Besides, our results supported the genome size stability after allopolyploidization, therefore rejecting the scenario of genome downsizing widespread accepted for angiosperms. Probably the most striking outcome of our phylogenetic investigations is the recurrent allopolyploidy in that genus and the strong bias of parental donors in the formation of allopolyploid taxa. Furthermore, our divergence time estimates revealed the recent and rapid speciation via allopolyploidy in the last two million years, which constitutes a first case of radiation in the old lineage of Ophioglossaceae. For our population genetics study, we found unprecedented genetic diversity within B. lunaria populations with a large number of heterozygotes that supports the outcrossing mating system. Thus, we presented the capabilities of dispersion and diversification of these Botrychium species to better understand the ancestral vascular plant mating system. Being a key element of this speciation model, we found a genetic signature indicative of a refuge for B. lunaria in the central Alps during the last glacial maximum, which has hosted individuals having a high allele richness that was secondarily dispersed after deglaciation with the maintenance of outcrossing in alpine grasslands.
    Undeniably, the genus Botrychium offers a unique opportunity to address the role of allopolyploidy and the importance of alternation of mating systems in plant speciation. This work is intended to be the starting point for further studies in evolutionary biology that ultimately will provide a better understanding of the life style of these enigmatic fern species.
  • Publication
    Accès libre
    Two new species of Gentianella (Gentianaceae) from Peru
    (2012)
    Pringle, James S
    ;
    Two new species of Gentianella (Gentianaceae, Gentianeae, Swertiinae), G. grantii and G. wayqecha, are described from Departamento Cusco, Peru. These two species differ from other Peruvian species of Gentianella in a combination of stems 10–100 cm long; no rosette of basal leaves; cauline leaves 10– 75 mm long; flowers in thyrses; and corollas 14–26 mm long, campanulate, and adaxially glabrous. The leaves of G. grantii consist of an appressed pseudopetiole and a spreading, narrowly elliptic-oblong to linear blade; the corollas are lavender; and the corolla lobes are 0.6–0.7× as long as the tube. Gentianella grantii is similar to G. lythroides, of Bolivia, but differs in having more closely spaced leaves and less deeply lobed corollas. The leaves of G. wayqecha are sessile, lanceolate to ovate; the corollas are rose-violet; and the corolla lobes are 0.75–1.35× as long as the tube. Gentianella wayqecha is similar to G. rapunculoides, of Colombia and Ecuador, and G. ruizii, of Peru, but differs from both in its adaxially glabrous corollas and from G. rapunculoides in its less deeply lobed corollas. Both G. grantii and G. wayqecha grow in moist habitats near tree line, and are known only from a area northeast of the city of Cusco.
  • Publication
    Accès libre
    Monophyly and relationships of the tribe Exaceae (Gentianaceae) inferred from nuclear ribosomal and chloroplast DNA sequences
    (2003)
    Yuan, Yong-Ming
    ;
    Wohlhauser, Sébastien
    ;
    Moller, Michael
    ;
    Chassot, Philippe
    ;
    Mansion, Guilhem
    ;
    ; ;
    Klackenberg, Jens
    Both chloroplast trnL (UAA) intron and nuclear ribosomal ITS sequences highly confirmed the monophyly of the tribes of the Gentianaceae defined by the recent classification, and revealed the tribe Exaceae as a basal clade just next to the basal-most lineage, the tribe Saccifolieae. Within the tribe Exaceae, Sebaea (except Sebaea madagascariensis) appeared as the most basal clade as the sister group to the rest of the tribe. The Madagascan endemic genera Gentianothamnus and Tachicrdenus were very closely related to each other, together standing as sister to a clade comprising Sebaea madagascariensis, Ornichia, and Exacum. The saprophytic genus Cotylanthera nested deeply inside Exacum. Sebaea madagascariensis was shown closer to the Madagascan endemic genus Ornichia than to any other sampled Sebaea species. Exacum appeared as the most derived taxon within this tribe. The topology of the phylogenetic trees conform with the Gondwana vicariance hypothesis regarding the biogeography of Exaceae. However, no evidence for matching the older relationships within the family to the tectonic history could be corroborated with various divergence time analyses. Divergence dating estimated a post-Gondwana diverging of the Gentianaceae about 50 million years ago (MYA), and the tribe Exaceae as about 40 MYA. The Mozambique Channel land-bridge could have played an important role in the biogeographic history of the tribe Exaceae. (C) 2003 Elsevier Science (USA). All rights reserved.
  • Publication
    Accès libre
    DE MACROCARPAEAE GRISEBACH (EX GENTIANACEIS) SPECIEBUS NOVIS VIII: FOUR NEW SPECIES FROM ECUADOR
    Two new species, Macrocarpaea claireae and M. quizhpei (Gentianaceae: Helieae), are described from the Huancabamba region of southern Ecuador. Macrocarpaea claireae occurs around Valladolid, adjacent to P. N. Podocarpus, and M. quizhpei occurs in the Nangaritza watershed. M. claireae is closely related to M. pringleana and M. sodiroana, yet differs notably in its glaucous-green, campanulate-urceolate calyx. Macrocarpaea quizhpei has affinities to M. dies-viridis, but differs in having a large, diffusely branched, open thyrse to 1.3 m high.
  • Publication
    Accès libre
    DE MACROCARPAEAE GRISEBACH (EX GENTIANACEIS) SPECIEBUS NOVIS X: A SYNOPSIS OF THE GENUS IN MONTANE ATLANTIC FORESTS OF BRAZIL
    ;
    Trunz, Vincent
    Outside of the principal distribution and major diversification of Macrocarpaea in the Andes, smaller groups of species are found in the Greater Antilles of the Caribbean, Mesoamerica, the Guayana Highlands, and montane Atlantic forests of Brazil. Here, a complete revision of the genus in the latter region is presented recognizing eight species that correspond to the entirety of Macrocarpaea sect. Tabacifoliae: M atlantica J.R. Grant & V. Trunz, sp. nov., M. dolichophylla J.R. Grant & V. Trunz, sp. nov., M. glaziovii Gilg, M. illecebrosa J.R. Grant, M. inesiae J.R. Grant & V. Trunz, sp. nov., M. obtusifolia (Griseb.) Gilg, M. orbiculata J.R. Grant & V. Trunz, sp. nov., and M. rubra Malme. These species occur primarily in humid coastal montane rainforests (Mata Atlântica), and two species also occur in campos rupestre montane savannas.
  • Publication
    Accès libre
    DE MACROCARPAEAE GRISEBACH (EX GENTIANACEIS) SPECIEBUS NOVIS VI: SEED MORPHOLOGY, PALYNOLOGY, AN INFRAGENERIC CLASSIFICATION , AND ANOTHER TWENTY-THREE NEW SPECIES LARGELY FROM COLOMBIA
    A brief survey of seed morphology and palynology in Macrocarpaea is discussed and illustrated by Scanning Electron Microscopy (SEM) photographs. An infrageneric classification is presented where four sections are recognized: sect. Tabacifoliae, sect. Macrocarpaea, sect. Magnolifoliae, and sect. Choriophylla. Another 23 new species, largely from Colombia, are here described and illustrated: Brazil (1): M. illecebrosa; Colombia (14): M. betancuriana, M. callejasii, M. gaudialis, M. gondoloides, M. gravabilis, M. gulosa, M. hilarula, M. jocularis, M. lacrossiformis, M. laudabilis, M. maryae, M. silverstonei, M. umerulus, and M. ypsilocaule; Ecuador (4): M. berryi, M. jactans, M. neillii, and M. voluptuosa; and Peru (4): M. chthonotropa, M. granpajatena, M. quechua, and M. xerantifulva.