Accueil > Séminaires de l’ISYEB


Les mardis de 12:30 à 13:30 dans l’amphithéâtre Rouelle, situé au rez de chaussée du bâtiment de la Baleine (derrière les wallabies) - Plan d’accès -

Le prochain séminaire aura lieu le 30 mai

- 30 mai : Hervé Sauquet, Université Paris-Sud, Lab. Écologie, Systématique, Évolution (ESE)

The ancestral flower of angiosperms and its early diversification : results from the eFLOWER project

Flowers are central to the biology and evolution of angiosperms (flowering plants). Here, we focus on the history of floral diversification through deep evolutionary time. A comprehensive understanding of global patterns of floral evolution has been prevented so far by the lack of an adequate morphological data set spanning all major angiosperm lineages. Using a new flexible and innovative approach, centered on a multi-user database (PROTEUS), we have built such a data set. Unlike most earlier studies of character evolution at the scale of angiosperms, we have recorded exemplar species instead of higher taxa such as genera or families. This approach allows for explicit reconstructions without assumptions about ancestral states or monophyly of supraspecific taxa, although we acknowledge that it also entails the risk of undersampling morphological variation. Importantly, the exemplar approach allows a direct match with the species sampled in molecular phylogenetic trees, providing the possibility to take branch lengths into account and to explore character evolution with probabilistic models. We report our first results from a data set of floral traits for 792 species representing all orders and 367 families (87%) of angiosperms, sampled from a recently published timetree calibrated with 136 fossil age constraints. Using this data set and tree, we reconstruct ancestral states for 27 key floral traits using parsimony, maximum likelihood, and Bayesian approaches and infer ancestral flowers for 15 key nodes (incl. Angiospermae, Mesangiospermae, Magnoliidae, Monocotyledoneae, Eudicotyledoneae, Pentapetalae, Rosidae, and Asteridae) as well as all extant orders of flowering plants. Further, we explore the sensitivity of our results to phylogenetic, dating, and model uncertainty. Importantly, all of our analyses converge on the same results in most cases, except near the root of the angiosperm tree, where parsimony continues to provide equivocal answers for some important floral traits, consistent with previous work. Lastly, the use of an explicit temporal framework for reconstructing ancestral states allows, for the first time, a direct comparison of inferred ancestral flowers with the known fossil record of each geological time interval. These results shed new light on long-standing questions on floral evolution across angiosperms, with important implications for a wide range of disciplines including Evo-Devo, pollination biology, and paleobotany.

- 6 juin : Julien Clavel, Institut de Biologie de l’École Normale Supérieure (IBENS).

Modelling phenotypic evolution on phylogenetic trees

- 13 juin : Vyacheslav Yurchenko, Associate Professor and Lab Head,
Laboratory of Molecular Protozoology, University of Ostrava, Czech Republic - SYNTHESIS UMR 7245

Trypanosomatids in NGS era

In this talk I will focus on two recently described trypanosomatid species which allow us to dissect molecular mechanisms governing some fundamental biological processes.

Part 1 will be devoted to Blastocrithidia spp., a clade of trypanosomatids with a unique nuclear genetic code. A limited number of non-canonical genetic codes have been described in eukaryotic nuclear genomes. Most involve reassignment of one or two termination codons as sense ones, but no code variant is known that would have reassigned all three termination codons. Here, we describe such a variant that we discovered in a clade of trypanosomatids comprising nominal Blastocrithidia spp. In these protists, UGA has been reassigned to encode tryptophan, while UAG and UAA (UAR) have become glutamate encoding. Strikingly, UAA and, less frequently, UAG also serve as bona fide termination codons. The release factor eRF1 in Blastocrithidia contains a substitution of a conserved serine residue predicted to decrease its affinity to UGA, which explains why this triplet can be read as a sense codon. However, the molecular basis for the dual interpretation of UAR codons remains elusive. Our findings expand the limits of comprehension of one of the fundamental processes in molecular biology.

Part 2 will deal with a recently established trypanosomatid-endosymbiont association. Recently, we described a novel symbiotic association between a kinetoplastid protist, Novymonas esmeraldas gen. nov., sp. nov., and an intracytoplasmic bacterium, “Candidatus Pandoraea novymonadis” sp. nov., discovered as a result of a broad-scale survey of insect trypanosomatid biodiversity in Ecuador. We characterize this association by describing the morphology of both organisms, as well as their interactions, and by establishing their phylogenetic affinities. Importantly, neither partner is closelyrelated to other known organisms previously implicated in eukaryote-bacterial symbiosis. This symbiotic association seems to be relatively recent, as the host does not exert a stringent control over the number of bacteria harbored in its cytoplasm. We argue that this unique relationship may represent a suitable model for studying the initial stages of establishment of endosymbiosis between a single-cellular eukaryote and a prokaryote. Based on phylogenetic analyses, Novymonas could be considered a proxy for the insect-only ancestor of the dixenous genus Leishmania and shed light on the origin of the two-host life cycle within the subfamily Leishmaniinae.

- 20 juin : Ray Tangney, Principal Curator Botany (Cryptogams), National Museum Wales, Cardiff

Systematics of the moss family Lembophyllaceae.

The Lembophyllaceae has undergone considerable revision during the last century, reflecting diverse views of the generic and familial relationships of this pleurocarpous moss family. During this time up to 15 genera have been included in the family, and as few as one, with the very existence of the family questioned. Similarly, the systematic position of the family has varied with changing generic composition. Based around the Australasian genus Lembophyllum, the family has been associated with a range of families including Brachytheciaceae, Meteoriaceae, Thamnobryaceae and Echinodiaceae. Recent analyses based on molecular data have supported a family of 14 genera, similar to classifications of the family in the early 20th century, and in contrast to those of the late 20th century, with strong relations to the Neckeraceae.This talk will introduce the morphology of the family and outline the impact of molecular analyses on the family concept and its biogeography, as well as ongoing research.

- 27 juin : André Nel, ISYEB

Les insectes fossiles, témoins privilégiés de l’histoire de la biodiversité terrestre

- 12 septembre : Roseli Pellens, ISYEB

- 19 septembre : Maël Montévil, ISYEB

- 10 octobre : Guillaume Sapriel, ABI, ISYEB

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