One of the most concerning characteristics of microbial biofilms is that of increased resistance to antimicrobial agents such as the commonly used biocide chlorhexidine (CHX). This can have huge impact on clinical, household and environmental settings. This is particularly alarming when it involves opportunistic pathogenic environmental organisms such as Delftia acidovorans as routine mitigation practices may fail to be effective. This thesis examines tolerance mechanisms of D. acidovorans biofilms exposed to CHX at inhibitory and sub-inhibitory concentrations. To achieve the study goals and objectives, a CHX-tolerant D. acidovorans strain (WT15), (Minimum Inhibitory Concentration; MIC-15 μg ml-1) was compared to a CHX-sensitive strain (MT51, MIC-1 μg ml-1) that was obtained by mutating the wild type strain using transposon mutagenesis. Specific morphological, structural and chemical compositional differences between the CHX-treated and untreated biofilms of wild type and mutant strains were documented using microscopic techniques including confocal laser scanning microscopy (CLSM), scanning transmission x-ray microscopy (STXM), transmission electron microscopy (TEM) and infrared (IR) spectroscopy. Molecular level changes between biofilms formed by these two strains due to CHX treatment were compared using whole-cell proteomic analysis (determined using differential in-gel electrophoresis, or DIGE) along with fatty acid methyl ester (FAME) analysis. The gene disrupted by transposon insertion that led to increased susceptibility to CHX in the mutant strain was identified as tolQ. CLSM revealed differences in biofilm architecture and thickness between the biofilms formed by strains WT15 and MT51. STXM analyses showed that WT15 biofilms contained two morpho-chemical cell variants; whereas, only one type was detected in MT51 biofilms. STXM and IR spectral analyses revealed that CHX-susceptible MT51 cells accumulated the highest levels of CHX, an observation supported by TEM wherein prominent changes in the cell envelope of CHX-susceptible MT51 cells were observed. DIGE analysis demonstrated that numerous changes in protein abundance occurred in biofilm cells following CHX exposure and that most of these proteins were associated with amino acid and lipid biosynthesis, protein translation, energy metabolism and stress-related functions. Overall, these studies indicate the probable role of the cell membrane and TolQ protein in CHX tolerance in D. acidovorans biofilms, in association with various proteins that are differentially-expressed.

Les carbapénèmes, β-lactamines possédant le spectre d’activité le plus large, sont souvent la dernière option thérapeutique des infections sévères dues à des germes multi-résistants. Les entérobactéries résistantes aux carbapénèmes, bien que rares en France, sont épidémiques voir même endémiques dans de nombreux pays. Cette résistance est principalement due à la production d’enzymes, les carbapénèmases, comme les enzymes de type KPC (Klebsiella pneumoniae Carbapenemase) dont il existe plusieurs variants. Les souches produisant ces enzymes ont rapidement disséminé dans de nombreuses régions du monde. Les objectifs de ce travail étaient de comprendre les mécanismes moléculaires de la multi-résistance aux antibiotiques des souches productrices de KPC et de déterminer lesfacteurs génétiques responsables de leur diffusion. Nous avons montré que le gène blaKPC est associé à un transposon de type Tn3, le transposon Tn4401, dont il existe trois isoformes.Nous avons aussi montré que Tn4401 est un transposon actif, capable de mobiliser le gèneblaKPC, et qui participe également à l’expression de ce gène par apport de séquencespromotrices. Puis, nous avons étudié une collection de souches de Klebsiella pneumoniae et de Pseudomonas aeruginosa exprimant le gène blaKPC. Nous avons ainsi montré que plusieurs clones de K. pneumoniae diffusent actuellement dans différentes régions du monde, avec unclone majoritaire, le clone ST258. Ces clones se caractérisent par des plasmides différents etpar la présence constante de Tn4401. Nous avons montré que plusieurs clones de P.aeruginosa disséminent dans les hôpitaux de Colombie et sont associés à des structuresgénétiques variables encadrant le gène blaKPC. Enfin, nous avons évalué une nouvelle méthode de détection des souches productrices de BLSE et de carbapénèmases, basée sur une puce à ADN. Cet outil s’est révélé rapide, sensible et spécifique pour tous les gènes recherchés. / Carbapenems are β-lactams with the broadest spectrum of activity and are often the last therapeutic option for treating severe infections due to multi-resistant organisms.Carbapenem-resistant Enterobacteriaceae remain rare in France, but are endemic in someareas. Carbapenem-resistance is mainly due to the production of carbapenemases, such as KPC (Klebsiella pneumoniae Carbapenemase). Several variants of KPC enzymes have beenidentified and KPC-producers are increasingly isolated worldwide. The aim of this study wasto determine the molecular mechanisms involved in multi-resistance of KPC-producers and tocharacterize the genetic elements involved in blaKPC gene mobilization and diffusion. Wehave described a new Tn3-based transposon, Tn4401, and characterized three isoforms. We have demonstrated that Tn4401 is an active transposon, capable of mobilizing blaKPC, and isinvolved in blaKPC gene expression. We have analysed several Klebsiella pneumoniae andPseudomonas aeruginosa isolates harboring the blaKPC-2 gene. We have assessed the spread ofseveral clones of K. pneumoniae isolates, including a major clone, ST258. These clones arecharacterized by different plasmids but an identical genetic structure, Tn4401. We havedemonstrated that several clones of P . aeruginosa are disseminating in Colombia, differingby MLST type, genetic support of blaKPC-2 and Tn4401-like structures. Finally, we have evaluated a new commercial system, based on microarray and dedicated to the identification of ESBL- and carbapenemase-producers. We found this method fast, sensitive and specific.

Les carbapénèmes constituent le traitement de dernier recours des infections associées à des germes multirésistants producteurs de -lactamases à spectre étendu. Les entérobactéries ont cependant développé des mécanismes de résistance à l’encontre de cette classe d’antibiotiques, notamment par la production de carbapénèmases. La carbapénèmase OXA-48 a rapidement disséminé en Europe et dans le pays du pourtour méditerranéen depuis 2010. Les objectifs de ce travail ont englobé, dans une première partie, la caractérisation de trois variants de la carbapénèmase OXA-48, possédant chacun des particularités phénotypiques ou génétiques. Nous nous sommes ensuite intéressés à l’épidémiologie de la carbapénèmase OXA-48 afin de comprendre ses mécanismes de dissémination puis à la variabilité de son environnement génétique. Le dernier objectif était de déterminer les facteurs génétiques à l’origine de la dissémination de la carbapénèmase OXA-48. Nous avons ainsi montré que les carbapénèmases de type OXA-48 bénéficient de tous les éléments moléculaires pour assurer leur succès : mobilisation par un transposon actif pour certains variants, transfert efficace de plasmides et dissémination clonale de souches. / Carbapenems are often the last therapeutic option for treating infections involving multiresistant ESBL-producing bacteria. Nevertheless, enterobacteria have developped resistance mechanisms toward this class of antibiotics, including carbapenemases production. Carbapenemase OXA-48 has rapidly spread throughout Europe and various countries of Mediterranean area since 2010. The aim of this work was first to characterize three variants of the carbapenemase OXA-48, each possessing phenotypic or genetic characteristics. We focused on the epidemiology of carbapenemase OXA-48 in order to understand the mechanisms of its dissemination and on the variability of its genetic environment. The last objective was to determine the genetic factors responsible for the spread of carbapenemase OXA-48. We have shown that the OXA-48-type carbapenemases possess all the molecular elements to ensure its success: mobilization by an active transposon for some variants, efficient transfer of plasmids and clonal spread of strains.

MicroRNAs (miRNAs) are an abundant and diverse class of small, non-protein coding RNAs that guide the post-transcriptional repression of messenger RNA (mRNA) targets in a sequence-specific manner. Hundreds, if not thousands of distinct miRNA sequences have been described, each of which has the potential to regulate a large number of mRNAs. Over the last decade, miRNAs have been ascribed roles in nearly all biological processes in which they have been tested. More recently, interest has grown in understanding how individual miRNAs evolved, and how they are regulated. In this work, we demonstrate that Transposable Elements are a source for novel miRNA genes and miRNA target sites. We find that primate-specific miRNA binding sites were gained through the transposition of Alu elements. We also find that remnants of Mammalian Interspersed Repeat transposition, which occurred early in mammalian evolution, provide highly conserved functional miRNA binding sites in the human genome. We also provide data to support that long non-coding RNAs (lncRNAs) can provide a novel miRNA binding substrate which, rather than inhibiting the miRNA target, inhibits the miRNA. As such, lncRNAs are proposed to function as endogenous miRNA "sponges," competing for miRNA binding and reducing miRNA-mediated repression of protein-coding mRNA targets. We also explored how dynamic changes to miRNA binding sites can occur by A-to-I editing of the 3 `UTRs of mRNA targets. These works, together with knowledge gained from the regulatory activity of endogenous and exogenously added miRNAs, provided a platform for algorithm development that can be used in the rational design of artificial RNAi triggers with improved target specificity. The cumulative results from our studies identify and in some cases clarify important mechanisms for the emergence of miRNAs and miRNA binding sites on large (over eons) and small (developmental) time scales, and help in translating these gene silencing processes into practical application.

Neisseria meningitidis is a commensal bacterium which sometimes causes serious disease in humans. Recent studies in numerous human pathogenic bacteria have shown that the stringent response contributes to bacterial virulence. Therefore, this study analyzed the regulation of the stringent response in meningococci and in particular of RelA as well as its contribution to ex vivo fitness in a strain- and condition- dependent manner by using the carriage strain α522 and the hyperinvasive strain MC58 in different in vitro and ex vivo conditions. Growth experiments revealed that both wild-type strains were almost indistinguishable in their ex vivo phenotypes. However, quantitative real time PCR (qRT-PCR) found differences in the gene expression of relA between both strains. Furthermore, in contrast to the MC58 RelA mutant strain α522 deficient in RelA was unable to survive in human whole blood, although both strains showed the same ex vivo phenotypes in saliva and cerebrospinal fluid. Moreover, strain α522 was depended on a short non-coding AT-rich repeat element (ATRrelA) in the promoter region of relA to survive in human blood. Furthermore, cell culture experiments with human epithelial cells revealed that in both strains the deletion of relA resulted in a significantly decreased invasion rate while not significantly affecting adhesion. In order to better understand the conditional lethality of the relA deletion, computational and experimental analyses were carried out to unravel differences in amino acid biosynthetic pathways between both strains. Whereas strain MC58 is able to synthesize all 20 amino acids, strain α522 has an auxotrophy for cysteine and glutamine. In addition, the in vitro growth experiments found that RelA is required for growth in the absence of external amino acids in both strains. Furthermore, the mutant strain MC58 harboring an ATRrelA in its relA promoter region showed improved growth in minimal medium supplemented with L-cysteine and/or L-glutamine compared to the wild-type strain. Contrary, in strain α522 no differences between the wild-type and the ATRrelA deletion mutant were observed. Together this indicates that ATRrelA interferes with the complex regulatory interplay between the stringent response pathway and L-cysteine as well as L-glutamine metabolism. It further suggests that meningococcal virulence is linked to relA in a strain- and condition- depended manner. In conclusion, this work highlighted the role of the stringent response and of non-coding regulatory elements for bacterial virulence and indicates that virulence might be related to the way how meningococci accomplish growth within the host environments. / Neisseria meningitidis ist ein kommensal lebendes, fakultativ pathogenes Bakterium, welches unter nicht vollständig verstandenen Umständen lebensbedrohliche Krankheitsbilder bei Menschen verursacht. Aktuelle Studien haben gezeigt, dass die stringente Antwort einen Einfluss auf die bakterielle Virulenz haben kann. Aus diesem Grund untersucht diese Arbeit die Regulation der stringenten Antwort, insbesondere die Rolle von RelA, sowie den Einfluss der stringenten Antwort auf die Ex-vivo-Fitness der Meningokokken. Die Ergebnisse wurden für den Trägerstamm α522 und den hyperinvasiven Stamm MC58 erhoben und miteinander verglichen. Wachstumsexperimente zeigten, dass sich beide Wildtyp-Stämme in ihren Ex-vivo-Phänotypen nicht unterscheiden. Jedoch wurden mittels quantitativer Echtzeit-PCR (qRT-PCR) Unterschiede zwischen beiden Stämmen in der Genexpression von relA gefunden. Zudem war die α522 relA Mutante im Gegensatz zu der MC58 relA Mutante nicht in der Lage, in menschlichem Vollblut zu überleben. Allerdings zeigten in Saliva und Liquor beide Stämme den gleichen Phänotyp. Außerdem war der Trägerstamm auf eine kurze, nicht-codierende AT-reiche Region (ATRrelA) in der Promotorregion von relA angewiesen, um im menschlichen Blut überleben zu können. Darüber hinaus zeigten Zellkulturexperimente mit humanen Epithelzellen, dass die Deletion relA die Invasionsrate in beiden Stämmen signifikant verringerte, obwohl die Adhäsionsrate durch die Deletion unbeeinflusst blieb. Um besser verstehen zu können, weshalb die Deletion von relA unter bestimmten Bedingungen letal ist, wurden mit In-silico- und experimentellen Analysen nach Unterschieden in den Aminosäurebiosynthesewegen beider Stämme gesucht. Es zeigte sich, dass Stamm MC58 in der Lage ist alle 20 Aminosäuren zu synthetisieren, während Stamm α522 eine Auxotrophie für Cystein und Glutamin aufweist. Ferner zeigten die In-vitro-Wachstumsversuche, dass RelA bei Aminosäuremangel essentiell für beide Stämme ist. Darüber hinaus zeigte eine MC58 Mutante mit einer ATRrelA –Kopie in der relA Promotorregion ein im Vergleich zum Wildtyp-Stamm verbessertes Wachstum in mit L-Cystein und/oder L-Glutamin angereichertem Minimalmedium. Gegensätzlich dazu zeigte der Stamm α522 keine Unterschiede im Wachstum zwischen dem Wildtyp und einer ATRrelA Deletions-Mutante. Dies deutet darauf hin, dass ATRrelA an dem komplexen regulatorischen Zusammenspiel der stringenten Antwort und dem L-Cystein- beziehungsweise dem L-Glutamin-Metabolismus beteiligt ist. Es lässt sich vermuten, dass RelA zu der Virulenz von Meningokokken in einer stamm- und umgebungsspezifischen Weise beiträgt. Abschließend hebt diese Arbeit die Rolle von kleinen regulatorischen Elementen für die bakterielle Virulenz hervor und postuliert, dass die Virulenz der Meningokokken auf ihrer Fähigkeit basiert, sich der durch den Wirt gegebenen Umgebung anzupassen.

High temperature stress (HTS) adversely affects reproduction in most plant species studied to date. HTS during flowering may result in an almost total inhibition of seed production in crop plants. Increasing our knowledge of the effects of HTS on seed production will aid the breeding of more thermotolerant crop plants and improve our understanding of the effects of stress on plants. An investigation of the effects of both drought and high temperature stress on the yields of barley, canola, flax, durum and spring wheat in five locations in Saskatchewan over a 25-year period was performed using multivariate analysis. Higher temperatures during June and July, when the plants were flowering, were correlated with reductions in yields of all the crops studied (except barley in June). A positive correlation between yields and precipitation during May and the winter preceding the growing season was observed.<p>In growth chambers, <i>Brassica napus</i> silique and seed production were inhibited during a ramping HTS treatment. This was due to a decrease in pollen germinability rather than a reduction in the number of flowers produced. HTS also caused reductions in megagametophyte fertility and disrupted embryo and/or seed development.<p>Transgenic plants were developed to overcome the effects of HTS on seed production. Two DNA constructs, one with the <i>Arabidopsis thaliana LEAFY</i> (<i>AtLFY</i>) promoter controlling <i>A. thaliana HEAT SHOCK PROTEIN 101</i> (<i>AtHSP101</i>) ORF expression and another with the <i>AtHSP101</i> promoter controlling <i>AtLFY</i> ORF expression, were inserted into <i>B. napus</i>. Other DNA constructs were made, using the constitutively expressed Cauliflower Mosaic Virus <i>35S</i> or the synthetic <i>EntCup4</i> promoters to control expression of the <i>AtHSP101</i> or <i>A. thaliana HEAT SHOCK TRANSCRIPTION FACTOR 3</i> (<i>AtHSF3</i>) ORFs. These constructs were inserted into both <i>B. napus</i> and <i>A. thaliana</i>. Transgenic plants were tested using a ramping temperature regime but were found not to have increased flower thermotolerance. During the manufacture of the DNA constructs it was determined that, in <i>A. thaliana</i>, 573 bp of <i>AtHSP101</i> had been copied between Terminal Inverted Repeats of a <i>Mu-Like Element</i> (<i>MULE</i>). This fragment was named <i>HSP101B</i>. In some transgenic <i>B. napus</i> and <i>A. thaliana</i> lines, containing 2046 bp of the <i>HSP101B</i> upstream regulatory region controlling <i>B</i>-glucuronidase (GUS) expression, cold-inducible GUS expression was observed. Methylation may have a role in control of endogenous <i>HSP101B</i> transcription.

Transposable elements (TEs) are found in nearly all eukaryotic genomes and are a major driving force of genome evolution. The hAT superfamily of TEs are found in a variety of organisms, including plants, fungi, insects and animals. To date, only 14 hAT TEs in the Aedes aegypti genome have been annotated as having a hAT transposase coding sequence. In this study, extensive bioinformatic approaches have been employed to find hAT TEs that encode transposases in the A. aegypti genome. A total of six newly-identified TEs belonging to the hAT superfamily were discovered in the A. aegypti genome. Furthermore, a computer program called TE Displayer was developed to analyze TEs in genome sequences. TE Displayer detects TE-derived polymorphisms in genome datasets and presents the results on a virtual gel image. TE Displayer enables researchers to compare TE profiles in silico and provides a reference profile for experimental analyses.

Transposable elements (TEs) are found in nearly all eukaryotic genomes and are a major driving force of genome evolution. The hAT superfamily of TEs are found in a variety of organisms, including plants, fungi, insects and animals. To date, only 14 hAT TEs in the Aedes aegypti genome have been annotated as having a hAT transposase coding sequence. In this study, extensive bioinformatic approaches have been employed to find hAT TEs that encode transposases in the A. aegypti genome. A total of six newly-identified TEs belonging to the hAT superfamily were discovered in the A. aegypti genome. Furthermore, a computer program called TE Displayer was developed to analyze TEs in genome sequences. TE Displayer detects TE-derived polymorphisms in genome datasets and presents the results on a virtual gel image. TE Displayer enables researchers to compare TE profiles in silico and provides a reference profile for experimental analyses.

High temperature stress (HTS) adversely affects reproduction in most plant species studied to date. HTS during flowering may result in an almost total inhibition of seed production in crop plants. Increasing our knowledge of the effects of HTS on seed production will aid the breeding of more thermotolerant crop plants and improve our understanding of the effects of stress on plants. An investigation of the effects of both drought and high temperature stress on the yields of barley, canola, flax, durum and spring wheat in five locations in Saskatchewan over a 25-year period was performed using multivariate analysis. Higher temperatures during June and July, when the plants were flowering, were correlated with reductions in yields of all the crops studied (except barley in June). A positive correlation between yields and precipitation during May and the winter preceding the growing season was observed.<p>In growth chambers, <i>Brassica napus</i> silique and seed production were inhibited during a ramping HTS treatment. This was due to a decrease in pollen germinability rather than a reduction in the number of flowers produced. HTS also caused reductions in megagametophyte fertility and disrupted embryo and/or seed development.<p>Transgenic plants were developed to overcome the effects of HTS on seed production. Two DNA constructs, one with the <i>Arabidopsis thaliana LEAFY</i> (<i>AtLFY</i>) promoter controlling <i>A. thaliana HEAT SHOCK PROTEIN 101</i> (<i>AtHSP101</i>) ORF expression and another with the <i>AtHSP101</i> promoter controlling <i>AtLFY</i> ORF expression, were inserted into <i>B. napus</i>. Other DNA constructs were made, using the constitutively expressed Cauliflower Mosaic Virus <i>35S</i> or the synthetic <i>EntCup4</i> promoters to control expression of the <i>AtHSP101</i> or <i>A. thaliana HEAT SHOCK TRANSCRIPTION FACTOR 3</i> (<i>AtHSF3</i>) ORFs. These constructs were inserted into both <i>B. napus</i> and <i>A. thaliana</i>. Transgenic plants were tested using a ramping temperature regime but were found not to have increased flower thermotolerance. During the manufacture of the DNA constructs it was determined that, in <i>A. thaliana</i>, 573 bp of <i>AtHSP101</i> had been copied between Terminal Inverted Repeats of a <i>Mu-Like Element</i> (<i>MULE</i>). This fragment was named <i>HSP101B</i>. In some transgenic <i>B. napus</i> and <i>A. thaliana</i> lines, containing 2046 bp of the <i>HSP101B</i> upstream regulatory region controlling <i>B</i>-glucuronidase (GUS) expression, cold-inducible GUS expression was observed. Methylation may have a role in control of endogenous <i>HSP101B</i> transcription.

Les différentes composantes des génomes et leur agencement sont issus de divers processus moléculaires. L'activité des éléments transposables (i.e. séquences d'ADN capables de se déplacer et se multiplier dans le génome) et l'augmentation du niveau de ploïdie (i.e. ensemble du nombre de chromosomes du noyau cellulaire) semblent avoir eu des rôles importants dans l'évolution de l'architecture des génomes des eucaryotes pluricellulaires. La polyploïdie se rencontre principalement chez les plantes mais elle se rencontre épisodiquement aussi dans des taxons animaux. De plus, plusieurs évènements de doublement de génome semblent avoir eu un impact sur la diversification des vertébrés. Les éléments transposables et la polyploïdie auraient des impacts non négligeables sur la diversification phénotypique des êtres vivants. Leur variation serait alors soumise à des processus sélectifs. Ces deux phénomènes pourraient interagir pour structurer les génomes. Selon différentes théories, l'augmentation du niveau de ploïdie aurait pour conséquence une augmentation du nombre d'insertions d'éléments transposables dans le génome. La plupart des études empiriques sont principalement basées sur des plantes allopolyploïdes et peu d'études se sont focalisées sur l'interaction entre la polyploïdie et les éléments transposables chez les animaux. Cette thèse de doctorat avait plusieurs objectifs. D'une part, cette thèse devait éclaircir l'histoire évolutive du complexe d'espèces Daphnia pulex. D'autre part, cette thèse avait pour but de tester l'effet du niveau de ploïdie sur un élément transposable de classe II, Pokey, en nature dans le complexe Daphnia pulex. Daphnia pulex est un petit crustacé d'eau douce. Les espèces de ce complexe se retrouvent dans les étangs et les lacs d'Amérique du Nord et d'Europe. Il existe une variation du mode de reproduction dans les populations (parthénogénétique cyclique ou obligatoire). Des lignées hybrides diploïdes et polyploïdes ont des origines multiples. Ce complexe présente un patron de polyploïdie géographique avec des diploïdes dans les régions tempérées et des polyploïdes dans les régions subarctiques et arctiques. L'importance de l'hybridation et le niveau de ploïdie dans ce complexe ont été réévalués. L'impact de la polyploïdie sur la densité de Pokey a été évalué en utilisant une technique de « TE display ». L'évolution des séquences de l'élément Pokey dans les lignées hybrides a été décrite avec des analyses phylogénétiques. Les données récoltées grâce à la cytométrie en flux combinées à l'analyse microsatellite ont révélé que la plupart des clones polyploïdes dans le complexe D. pulex sont triploïdes et non tétraploïdes comme le suggéraient les études antérieures. Les clones triploïdes sont probablement issus d'interactions entre des populations sexuées et asexuées. Diverses analyses sur les données microsatellites ont permis de séparer les populations hybrides des espèces dont elles sont issues. Les populations hybrides sont composées d'hybrides diploïdes et polyploïdes avec des mitochondries D. pulex et certaines lignées avec des mitochondries D. pulicaria. Les analyses conjuguées des données microsatellites et d'un gène nucléaire ont permis d'éclaircir les relations évolutives entre un groupe d'espèces où le maintien du polymorphisme ancestral et l'hybridation affectent les relations phylogénétiques observées en n'analysant qu'un seul gène. Cette étude montre que l'hybridation et l'introgression ont joué un rôle important dans l'évolution de ce complexe. Le nombre d'insertions TE a été comparé entre des diploïdes (14) et des polyploïdes (13) hybrides en utilisant une technique de « TE display ». Bien que le nombre moyen de sites d'insertion était plus élevé chez les polyploïdes que chez les diploïdes cette différence n'était pas statistiquement significative. De nombreux évènements de recombinaisons ont été révélés dans des allèles de Pokey dans des lignées diploïdes et polyploïdes du complexe pulex. Des analyses phylogénétiques et de recombinaison ont montré que la recombinaison est une force majeure qui façonne l'évolution du transposon Pokey. Cette thèse de doctorat présente donc divers patrons et processus génétiques se déroulant lors de la formation du complexe d'espèces Daphnia pulex. L'hybridation et la polyploïdie semblent avoir eu un impact significatif sur la diversification et possiblement sur l'adaptation de populations à différents environnements. L'absence d'augmentation du nombre d'insertions d'éléments transposables pourrait être expliquée par une augmentation de ceux-ci dans les lignées diploïdes hybrides parentes. L'intégration d'une vision écosystémique du génome pourrait permettre de mieux comprendre comment les génomes se structurent au cours de l'évolution. Des études en écologie évolutive et expérimentales permettraient de répondre à différentes hypothèses proposées lors de cette étude. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Polyploïdie, hybridation, transposon, complexe d'espèces, Daphnia pulex