Étude de la diversité des épibiontes bactériens associés au céphalothorax de la crevette hydrothermale Rimicaris exoculata

La crevette Rimicaris exoculata est une espèce hydrothermale endémique des sites de la Ride Médio-Atlantique. Elle représente I espèce majoritaire sur la plupart des sites qu elle colonise. Ce crustacé possède la particularité d avoir un céphalothorax hypertrophié â l intérieur duquel se développe une communauté épibiotique bactérienne dense. Ce travail de thèse s est concentré sur l observation des changements dans la communauté épibiotique du céphalothorax de R. exoculata au cours de son cycle de vie. Pour ensuite, rechercher qu elles étaient les métabolismes bactériens mis en jeu dans cette communauté. Ce travail a permis de confirmer que cette communauté épibiotique est dominée par deux phylotypes, les Epsilonproteobacteria et les Gammaproteobacteria. Ils sont éliminés et recolonises le céphalothorax après chaque mue de l hôte et sont détectés dans l environnement (transmission horizontale). Cependant, la proportion relative de ces deux phylotypes semble varier au cours du cycle de vie de l hôte. Les voies productrices d énergie que sont la méthanotrophie, la sulfo-oxydation/réduction et l hydrogénotrophie ont été détectées chez les épibiontes du céphalothorax ainsi que les voies autotrophes (cycles rTCA et Calvin) qu elles sont supposées alimenter. Les résultats ont également montré que les voies basées sur l oxydation des composés soufrés sembleraient majoritaires et en activité constante, alors que les voies basées sur l oxydation du méthane et de l hydrogène seraient dépendantes des conditions géochimiques du milieu de vie de l hôte. Cette étude apporte de nouvelles hypothèses sur la relation entre les épibiontes du céphalothorax et Rimicaris exoculata.The shrimp Rimicaris exoculata is an endemic hydrothermal species of the Mid-Atlantic Ridge sites. It s the dominant species on several hydrothermal vent sites. This crustacean has an enlarged gill chamber, harboring a dense ectosymbiotic community. Until now, their acquisition and their metabolic pathways were not fully understood. This study focused on the analyses of the possible differences in the epibiotic community among the gill chamber epibiotic community along R. exoculata life cycle. Then, we have looked for the bacterial metabolisms suspected to occur among this community. This work confirmed that the epibiotic community is dominated by two phylotypes: Epsilonproteobacteria and Gammaproteobacteria. They are eliminated and then recolonised the cephalothorax after each moult. In addition, they were detected in the environment (horizontal transmission). However, the relative proportion of these phylotypes seemed to vary along the host life cycle (eggs/larvae versus juvenile/adult). The energetic pathways such as the methanotrophy, the sulfur-oxidation/reduction and the hydrogenotrophy were detected from the cephalothorax epibionts as well as the autotrophic pathways (rTCA and Calvin cycles). Results also showed that the oxidation of the sulphur compounds seemed to be the major pathways with constant activity, whereas the oxidation of methane and hydrogen seemed to be threshold dependent and so linked to the geochemical conditions of the host life environment. This study broadened our view on the relations between the cephalothorax epibionts and the hydrothermal shrimp Rimicaris exoculata.BREST-BU Droit-Sciences-Sports (290192103) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

The obligatory contour principle in African and European varieties of French

This study provides evidence that the role of the Obligatory Contour Principle (OCP) in substrate languages is reflected in prosodic systems of contact varieties of French. We have compared two contact varieties: Central African French, a variety of French spoken by L1 speakers of Sango a lexical tone language where the constraint is not respected, and Burundi French, which is spoken by L1 speakers of Kirundi, a lexical tone language where the OCP plays an important role in the distribution of tones. Our data indicate that clashes are permitted in the former, but avoided in the latter

La variation prosodique dialectale en français : données et hypothèses

cote interne IRCAM: Avanzi12bNone / NoneInternational audienceDans cet article, nous comparons la prosodie de 6 variétés de français parlées en France (Paris et Lyon), en Belgique (Tournai et Liège) et en Suisse (Genève et Neuchâtel). L’objectif est de voir si les 6 variétés considérées peuvent être discriminées sur la base de critères exclusivement prosodiques. Les enregistrements du même texte lu par 4 locuteurs pour chacune des variétés sont transcrits, alignés et codés pour l’étude de l’accentuation, du phrasé et du rythme. Les résultats d’une méthode de classification non- supervisée guidée par les hypothèses (top-down) aboutissent à des résultats cohérents avec une classification a priori des variétés sur une échelle d’éloignement dialectal, alors qu’une méthode de classification non-supervisée émergente (bottom-up) donne lieu à des résultats plus contrastés

Simulating the dynamics of epiphytic diatom metacommunity in stream environments contaminated with heavy metals

International audienceHeavy-metal pollution may drive succession in freshwater diatom communities towards more pollution tolerant species, resulting in an increased tolerance of communities but also in loss of species diversity. Using models is the best way to have a fast and robust estimation of natural-community evolution to study efficiently the microorganism community dynamics in freshwater environments. However until nowadays, no ecotoxicological study dealing with modeling diatom dynamics in heavy-metal contaminated stream environments was established. A means of considering population level in ecotoxicology is the "demographic" methodology. It consists of introducing effects of pollutants on demographic parameters into models of population dynamics. When the study deals with several species belonging to a same group, the community must be considered. And when several communities are considered, some processes emerge like spontaneous migration, non-spontaneous migration or "actions at distance". So modeling species-structured communities with matrix methods can be applied to spatial fragmented populations. The dimensions of these models describing real systems (demography, migrations) increase with the number of spatial patches and the number of species considered, which have dissuaded all scientists to work on stream diatom communities. Our work aimed to integrate pollutant effects in such a multi-region model with two different time scales. We developed a model of a theoretical river network based upon the catchment basin of the Vienne river located in the Limousin region (France) with low autoecological variations. We have selected 8 diatom species adnated to one of the most common macrophyte in the limousin rivers, Myriophyllum alterniflorum (Haloragaceae) and two heavy metals (copper and cadmium) as the toxic compounds. These metals were chosen because they are common pollutants of stream environments and they have a high toxicity associated with a strong potential for bioaccumulation. Furthermore, their persistence in aquatic systems lead to their registration on the European Union's blacklist of harmful substances since many years. Our theoretical river network consists of 6 asymmetric levels and 14 patches. The patch distribution among the levels is based on the geography of the 14 studied in situ localities. This allows a better comprehension of the ecotoxicological impacts of heavy metals on macrophyte-associated diatom communities. Our multi-area model considers toxicity in terms of survival and colonization reduction through dose-response curves established from our in situ data. We hypothesized that the maximum heavy-metal concentrations (measured in situ in each studied locality) are discharged when the pollution occurs. Species composition, spatial distribution, demographic and migration processes were taken into account to estimate community responses to this really realistic scenario of pollutant discharge. As a breakthrough, our results highlight that in cadmium-polluted areas, diatom migrations play here an important role in the survival of three species: Achnanthes microcephala, Cocconeis placentula and Navicula simplex. This study brings important information for health environmental projects which must considered not only the pollution frequency but also the sustainability of the biological substrate for periphyton

Prorocentrum rivalis sp. nov. (Dinophyceae) and its phylogenetic affinities inferred from analysis of a mixed morphological and LSU rRNA data set

International audienceA new freshwater epiphytic Prorocentrum species, Prorocentrum rivalis, from the temperate region of the Haute-Vienne, France, is described. This species is the third freshwater species identified among approximately 60 marine Prorocentrum species. This new species is described using scanning electron microscope and phylogenetic analyses by a polyphasic approach (LSU rRNA sequences combined with 9 morphological characters). The phylogenetic analysis attests that P. rivalis is close to other planktonic freshwater species and the freshwater Prorocentrum clade is evolutionarily derived from an epiphytic freshwater prorocentroid ancestor. The unique marine species in the freshwater clade results from an ecophysiological reversion. P. rivalis differs from other epiphytic taxa by its rarity, its temperate distribution and its ecophysiological needs. The phylogeny confirms also that all planktonic Prorocentrum species are evolutionarily derived from epiphytic/benthic ancestors

Variations in the realization of the French Accentual Phrase in the light of language contact

In this paper we discuss the French prosodic system in the light of language contact. Similar data of three contact varieties are compared with two varieties spoken in monolingual contexts. The data are semi-automatically processed, and three prosodic features are analyzed: metrical weight of the realized APs, respect of AP-restructuring rules and realizations of sandhi phenomena. Rhythmic constraints and speech rate measurements are also considered. Our findings suggest that the prosodic systems of the contact varieties share several features with word prosodic systems.

Speech prosody of French regional varieties

This paper compares the prosody of 6 varieties of French spoken in three different areas: France (Paris and Lyon), Belgium (Tournai and Liège), and Switzerland (Geneva and Neuchâtel). The objective is to adress whether some regional varieties, namely those of Geneva and Tournai, are closer to standard French (i.e. the varieties spoken in France, represented here by Paris and Lyon) than others (Neuchâtel and Liège). The recordings of the same text read by 4 speakers representing each variety were semi-automatically processed in order to study accentuation, speech rate and rhythm, and 8 prosodic measures that can possibly discriminate the 6 varieties were compared. A top-down clustering supported evidence for the expected classification with regard to the “standard” varieties, while a bottom-up clustering pointed out a more contrasted configuration.

Regional variations of speech rhythm in French : in search of lost times

This paper addresses the relevancy of speech rhythm acoustic measures for the description of some standard, regional and contact varieties of French. First, the limitations of conventional measures of speech rhythm, such as (%V, ΔC) [Ramus et al. 1999] and Pairwise Variability Index [Grabe & Low 2002], for the description of French regional variations is discussed. Then, alternative acoustic measures of speech rhythm, based on long-term characteristics associated with timing (regularity of accentual phrases) and tempo (articulation rate, speech rate) are introduced and discussed. A comparison with the conventional measures indicates that long-term measures conduct to a classification which is more consistent with the expected classification, either for the description of continuous similarities or categorical grouping.