Maintien d'une zone hybride de gueules de loup (Antirrhinum majus) : rôle de quelques interactions biologiques

Les zones hybrides offrent un regard privilégié sur les processus évolutifs. En cas d'hybridation, l'intégrité des espèces parentales ne peut être maintenue que si des forces évolutives compensent le flux de gènes. Je me suis attachée à en comprendre les mécanismes écologiques en étudiant le rôle des espèces en interaction dans la dynamique d'une zone hybride entre Antirrhinum majus pseudomajus, à fleurs magenta, et A. m. striatum, à fleurs jaunes. Les deux sous-espèces présentent une morphologie florale similaire et ont les mêmes pollinisateurs : des bourdons et des xylocopes. L'analyse de la fructification et des dégâts subis par les plantes suggère un rôle des pollinisateurs et des charançons dans la sélection contre les hybrides et donc dans la stabilisation de la zone hybride. Après avoir vérifié que les bourdons perçoivent les variations de couleurs dans la zone hybride, j'ai montré qu'une augmentation de la diversité des couleurs, comme celle causée par l'apparition d'hybrides de générations tardives, entraîne une augmentation de la constance des pollinisateurs et donc de l'homogamie, ce qui contribuerait à l'isolement prézygotique. Enfin, une analyse spatiale suggère une fréquence-dépendance positive de la sélection liée aux taux de visites des pollinisateurs et un moindre taux de visites de certains hybrides, qui contribuerait à l'isolement postzygotique. Les pollinisateurs peuvent donc participer au maintien des différences entre espèces interfertiles, y compris dans les systèmes où les taxons partagent les mêmes pollinisateurs. De plus, le maintien des zones hybrides pourrait, dans certains cas, résulter des actions cumulées de plusieurs agents biologiques.Hybrid zones provide an insight into evolutionary processes. When hybridization occurs, the integrity of the parental species is maintained only if some evolutionary forces balance gene flow. In my research I focus on understanding the ecological mechanisms subjacent to this process. I assess the role of interacting species in the dynamics of a hybrid zone between the magenta flowered Antirrhinum majus pseudomajus and the yellow flowered A. m. striatum. Both subspecies have a similar floral morphology and share the same pollinators: bumblebees and carpenterbees. Analyses of fruit set and plant damage suggest a role of pollinators and of weevils in the selection against hybrids, and hence in the stabilization of the hybrid zone. After verification that bumblebees are able to perceive the flower colour variation in the hybrid zone, I show that an increase in colour diversity, like that occurring as late generation hybrids are formed, leads to an increase in the level of pollinator constancy and hence in homogamy. This may contribute to prezygotic isolation. Finally, a spatial analysis suggests a positive frequency dependence of the selection acting through the pollinators' visitation rates, and a low visitation rate to some hybrids which may contribute to postzygotic isolation. The results indicate that pollinators can play a role in maintaining the differences between interfertile plant species, even in systems where plant taxa share pollinators. Moreover, hybrid zone maintenance may be the result of the accumulated actions of several biotic agents

Maintenance of a snapdragon (Antirrhinum majus) hybrid zone (role of some biotic interactions)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Expression of the retrotransposons Surcouf and Blackbeard in the marine diatom Phaeodactylum tricornutum under thermal stress

International audienceTransposable elements (TEs) are mobile DNA sequences thought to be involved in the genomic response toenvironmental stresses of organisms. The thermal stress behaviour of two retrotransposons (Surcouf and Blackbeard ) wasinvestigated in the genome of two strains of the marine diatom Phaeodactylum tricornutum. Using quantitative reversetranscriptase polymerase chain reaction, the retrotransposon expression pattern was investigated after thermal stressesand compared with that of the small heat-shock protein (shsp). While the expression of Blackbeard was not affected bytemperature changes, the retroelement Surcouf was markedly overexpressed in response to high temperature incorrelation with shsp overexpression. An in silico analysis investigated the presence of regulatory heat-inducible motifssuch as heat-shock elements, stress response elements and CCAAT boxes within the promoters of shsp andretrotransposons in the genome of P. tricornutum. The results of mRNA quantification are supported by the presenceof heat-shock response motifs found in the promoters of shsp and the retrotransposon Surcouf

Transcriptional response of stress-regulated genes to cadmium exposure in the cockle Cerastoderma glaucum from the gulf of Gabès area (Tunisia)

International audienceThis study investigates cadmium effects on key messenger RNA (mRNA) expression (MT, MnSOD, CuZnSOD, CAT, ABCB1, HSP70, and CO1) by qPCR in the cockle Cerastoderma glaucum after chronic exposure to two high but environmentally relevant concentrations of CdCl2 (50 μg/L and 5 mg/L) for 12 h to 18 days. Cd accumulation measured in cockles' tissues is significantly higher in both treatment conditions compared to controls and in a dose-dependent manner. Stress on stress tests performed at different times of the experiment clearly demonstrated that exposure to both concentrations of Cd significantly affects cockle survival time in air. Important changes in gene transcription were also highlighted. In particular, MT, HSP70, CAT, and CuZnSOD seem to be relevant biomarkers of Cd exposure because (1) their mRNA levels increase upon exposure and (2) they are highly correlated to Cd accumulation in tissues. Results may be useful for control strategies and for the use of cockles as sentinel organisms

An introduction to the vast world of transposable elements – what about the diatoms?

International audienceTransposable elements (TEs) are DNA sequences that are able to move and replicate within the genomes of virtually all organisms, ranging from animals to plants, and also including protozoans, bacteria and diatoms. Initially considered to be ‘junk DNA’ with no function, TEs are now thought to play a pivotal role in the evolution of genomes and organisms. This review is intended to provide non-specialists with an introduction to the world of TEs by summarizing the information available about these elements, ranging from their impact on genome structure to their potential involvement in the evolution of species. In this review, we propose to bring together what is known about the TEs and provide an overview of recent advances concerning TEs in diatoms

Characterization of irritans mariner-like elements in the olive fruit fly Bactrocera oleae (Diptera: Tephritidae): evolutionary implications

International audienceGenomic variation among species is commonly driven by transposable element (TE) invasion; thus, the pattern of TEs in a genome allows drawing an evolutionary history of the studied species. This paper reports in vitro and in silico detection and characterization of irritans mariner-like elements (MLEs) in the genome and transcriptome of Bactrocera oleae (Rossi) (Diptera: Tephritidae). Eleven irritans MLE sequences have been isolated in vitro using terminal inverted repeats (TIRs) as primers, and 215 have been extracted in silico from the sequenced genome of B. oleae. Additionally, the sequenced genomes of Bactrocera tryoni (Froggatt) and Bactrocera cucurbitae (Diptera: Tephritidae) have been explored to identify irritans MLEs. A total of 129 sequences from B. tryoni have been extracted, while the genome of B. cucurbitae appears probably devoid of irritans MLEs. All detected irritans MLEs are defective due to several mutations and are clustered together in a monophyletic group suggesting a common ancestor. The evolutionary history and dynamics of these TEs are discussed in relation with the phylogenetic distribution of their hosts. The knowledge on the structure, distribution, dynamic, and evolution of irritans MLEs in Bactrocera species contributes to the understanding of both their evolutionary history and the invasion history of their hosts. This could also be the basis for genetic control strategies using transposable elements

Flower colour variation across a hybrid zone in Antirrhinum as perceived by bumblebee pollinators

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