Добірка наукової літератури з теми "Mytilus edulis – Adaptation"

Early ontogenetic adaptations reflect the evolutionary history of a species. To understand the evolution of the deep-sea fauna and its adaptation to high pressure, it is important to know the effects of pressure on their shallow-water relatives. In this study we analyse the temperature and pressure tolerances of early life-history stages of the shallow-water species Mytilus edulis . This species expresses a close phylogenetic relationship with hydrothermal-vent mussels of the subfamily Bathymodiolinae. Tolerances to pressure and temperature are defined in terms of fertilization success and embryo developmental rates in laboratory-based experiments. In M. edulis , successful fertilization under pressure is possible up to 500 atm (50.66 MPa), at 10, 15 and 20°C. A slower embryonic development is observed with decreasing temperature and with increasing pressure; principally, pressure narrows the physiological tolerance window in different ontogenetic stages of M. edulis , and slows down metabolism. This study provides important clues on possible evolutionary pathways of hydrothermal vent and cold-seep bivalve species and their shallow-water relatives. Evolution and speciation patterns of species derive mostly from their ability to adapt to variable environmental conditions, within environmental constraints, which promote morphological and genetic variability, often differently for each life-history stage. The present results support the view that a direct colonization of deep-water hydrothermal vent environments by a cold eurythermal shallow-water ancestor is indeed a possible scenario for the Mytilinae, challenging previous hypothesis of a wood/bone to seep/vent colonization pathway.

In molluscs, the shell secreted by mantle tissue during the biomineralization process is the first barrier against predators and mechanical damage. Changing environmental conditions, such as ocean acidification, influence shell strength and thus protection of the soft body within. Mussels are marine bivalves with important commercial and ecological value worldwide. Despite this importance, the proteins involved in the biomineralization and pigmentation processes in Mytilus spp. remain unclear, as does taxonomy of Mytilus taxa, though there have been many molecular studies. To further understanding in these areas, this study aimed to characterize and compare mantle transcriptomes of four mussel taxa using next generation sequencing. Mussels representing four taxa, were collected from several localities and RNA from mantle tissue was extracted. RNA sequences obtained were assembled, annotated and potential molecular markers, including simple sequence repeats (SSRs) and single nucleotide polymorphisms (SNPs) were identified. Candidate contigs putatively related to biomineralization and pigmentation processes were then selected and several transcripts were chosen for phylogenetic analyses from the Bivalvia class. Transcriptome comparisons between Mytilus taxa, including gene ontology (GO) enrichment analysis and orthologues identification were performed. Of assembled contigs, 46.57%, 37.28% and 17.53% were annotated using NCBI NR, GO and Kyoto Encyclopedia of Genes and Genomes databases, respectively. Potential SSRs (483) and SNPs (1,497) were identified. Results presented a total of 1,292 contigs putatively involved in biomineralization and melanogenesis. Phylogenetic analyses of α-carbonic anhydrase, chitinase and tyrosinase revealed complex evolutionary history and diversity of these genes, which may be a result of duplication events or adaptation to different environments in mussels and other bivalves. Enrichment analyses revealed GO terms associated with pH and thermal response in Mytilus edulis from the North Sea and M. galloprovincialis from the Mediterranean Sea. The phylogenetic analysis within the genus Mytilus revealed M. californianus and M. coruscus to be genetically more distant from the other taxa: M. trossulus, M. edulis, M. chilensis and M. galloprovincialis. This work represents the first mantle transcriptome comparison between Mytilus taxa and provides contigs putatively involved in biomineralization.

Alterations of membrane lipid composition (cholesterol, phospholipids and their fatty acids) in response to various temperature changes were studied in blue mussels Mytilus edulis L. from the White Sea. Lipid composition changes after acute temperature stress, especially a temperature drop, included a significant reduction of the membrane phospholipid content directly (1 h) after return to the initial temperature, which was presumably a consequence of a non-specific stress reaction in the mussels. A longer recovery period (24 h) as well as long-term temperature acclimation (14 days) induced changes in gill fatty acid composition (for instance, a rise in phospholipid unsaturated fatty acids under low temperature impact), indicating ‘homeoviscous adaptation’ to maintain the membranes in response to temperature fluctuations. Moreover, the gill cholesterol level in mussels varied especially at long-term temperature exposure.

Abstract Environmental adaptation of molluscs during evolution has led to form biomineral exoskeleton – shell. The main compound of their shells is calcium carbonate, which is represented by calcite and/or aragonite. The mineral part, together with the biopolymer matrix, forms many types of microstructures, which are differ in texture. Different types of internal shell microstructures are characteristic for some bivalve groups. Studied bivalve species (freshwater species – duck mussel (Anodonta anatina Linnaeus, 1758) and marine species – common cockle (Cerastoderma edule Linnaeus, 1758), lyrate Asiatic hard clam (Meretrix lyrata Sowerby II, 1851) and blue mussel (Mytilus edulis Linnaeus, 1758)) from different locations and environmental conditions, show that the internal shell microstructure with the shell morphology and thickness have critical impact to the ability to survive in changing environment and also to the probability of surviving predator attack. Moreover, more detailed studies on molluscan structures might be responsible for create mechanically resistant nanomaterials.

Blue mussels, Mytilus edulis, inhabiting tidal zones, are naturally exposed to fluctuating environmental conditions (e.g., fluctuations in temperature and salinities), while horse mussels, Modiolus modiolus, live under relatively invariable shelf water conditions. The present investigation tested the hypothesis: blue mussels, in comparison to horse mussels, have an increased ability to tolerate the stress of pollution combined with low salinity. To assess the response of blue mussels and horse mussels to oil pollution at seawater salinities of 25 psu (normal) and 15 psu (low), we used a combination of heart rate and lipid composition as physiological and biochemical indicators, respectively. A sharp decrease in heart rate as well as important fluctuations in cardiac activity was observed under all oil concentrations. Modifications in the concentrations of the main membrane lipid classes (phosphatidylcholine, phosphatidylethanolamine, and cholesterol) and storage lipids (primarily triacylglycerols) in response to different crude oil concentrations were time- and dose-dependent. Both chosen indicators showed a high sensitivity to crude oil contamination. Furthermore, both bivalve species showed similar responses to oil pollution, suggesting a universal mechanism for biochemical adaptation to crude oil pollution.

Dans un contexte de réchauffement climatique et d'anthropisation, les organismes colonisant les espaces côtiers sont, et seront soumis, à des variations importantes de leur milieu de vie. Parmi ces organismes, la moule bleue Mytilus edulis constitue une espèce clé des écosystèmes intertidaux et est utilisée comme sentinelle. Au cours de cette thèse, des moules collectées sur des sites présentant des niveaux de contamination contrastés ont été conditionnées à deux niveaux de température différents avant une exposition à un stress thermique aigu. Des analyses protéomiques ont été réalisées pour explorer les effets de ces stress sur l'homéostasie des protéines. Une forte mortalité est observée exclusivement pour les individus issus du site pollué et conditionnés à des températures modérées. Chez les individus issus du site propre, une abondance de protéines de stress thermique et une sur-expression d'acteurs indiquant la mise en place d'un métabolisme anaérobie est observée. Les individus conditionnés à des températures plus élevées ont une meilleure réponse vis-à-vis des individus conditionnés aux températures modérées. Pour les moules provenant du site contaminé les réponses protéiques sont bien moins nettes et tendent à démontrer un effet additif délétère de la contamination et de la température. Là encore, les individus conditionnés aux températures les plus élevées répondent mieux. En conclusion, les individus au trait de vie non contaminés affichent de meilleures réponses physiologiques que les individus contaminés. De plus, les organismes dont l'historique thermique est favorable, i.e. conditionnés à des températures plus élevées, ont également des réponses améliorées
Intertidal organisms live in a fluctuating environment. The blue mussel Mytilus edulis is a key species of those ecosystems and are largely use as sentinel species. Global warming associated with anthropization will expose mussels to contaminations together with increased temperatures. In addition, more frequent heatwaves are expected. In this work, mussels were collected at two sites depicting contrasted levels of contamination and thermal exposure in microcosm were conducted. Two acclimation scenarios were set up prior to exposure to an identical acute thermal stress. In order to decipher joint effects of acclimation and contamination on protein homeostasis, gill proteome comparisons were performed. High mortality was observed only for mussels collected at the contaminated site and acclimated to current temperatures. Concerning gill proteome analysis, organisms from the pristine site exhibit high abundance of thermal stress proteins. Proteoforms involved in anaerobic metabolism were also up-regulated. Interestingly, mussels acclimated to the higher temperatures show an enhanced response compare to the one acclimated to current temperatures. Concerning mussels from the contaminated site, the response appears more confusing, excepted for heat stress protein response. This may indicate deleterious effects of combined contamination and heat stress. Therefore, organisms acclimated to higher temperature display improved responses. In conclusion, mussels with a clean life history show better physiological abilities than individuals with contaminated life history. Moreover, organisms prepared to heat stress by higher acclimation temperatures also develop a more effective response

Les génomes sont affectés par des régimes de sélection conflictuels. Ceci est particulièrement bien illustré par le concept de barrière semi-perméable au flux génique, issu de la littérature des zones hybrides. Certains gènes contribuent à empêcher le mélange entre lignées génétiques différenciées, soit parce qu'ils participent à l'adaptation aux conditions environnementales locales, soit parce qu'ils sont incompatibles avec les gènes d'autres lignées. D'autres parties du génome sont soit neutres, soit soumises à une sélection qui tend à homogénéiser les différentes lignées entre elles. Dans la première partie de cette thèse, des modèles d'évolution de l'isolement reproductif sont présentés pour expliquer les patrons d'isolements observés dans les expériences d'hybridation au laboratoire. Par modélisation classique d'incompatibilités génétiques de type Dobzhansky-Muller, il est montré que l'asymétrie et la complexité des incompatibilités sont imparfaitement expliquées par un filtre évolutif, c.a.d. une vitesse d'accumulation différente entre types d'incompatibilité. Une approche complémentaire de modélisation quantitative à l'aide d'une extension du modèle géométrique de Fisher a permis de préciser quelles conditions de divergence entre lignées isolées conduisaient à un effet fortement délétère des mutations dans les génotypes hybrides. L'importance relative du niveau d'épistasie moyen, de la distribution des effets des mutations et des modalités de l'adaptation de chaque lignée est discutée. La seconde partie de cette thèse profite des avancées techniques de la génomique pour étudier l'histoire de la spéciation et de l'adaptation dans un complexe d'espèces non-modèles, les moules du genre Mytilus. Une méthode statistique d'inférence de scénarios de spéciation est présentée. Les résultats montrent que les moules Européennes ont connu une histoire complexe de divergence stricte suivie d'une période de connectivité périodique. En accord avec le concept de barrière semi-perméable au flux génique, il est montré que les taux d'introgression sont hétérogènes le long du génome. Ensuite, des scans génomiques de la différenciation ont été menés entre paires de populations du complexe d'espèces. L'analyse de la variation génétique et des généalogies d'allèles sur une échelle chromosomique localisée a permis de reconstituer l'histoire évolutive de plus de 1000 régions du génome des moules. Cette analyse a révélé qu'une cause majeure, mais insoupçonnée, de la différenciation génétique intraspécifique est l'introgression différentielle d'allèles étrangers. Globalement, cette thèse montre non seulement le rôle majeur de la biogéographie de la spéciation, c.a.d. des patrons temporels et spatiaux du flux de gènes, dans notre compréhension de la biodiversité actuelle, mais aussi sa surprenante complexité et l'étendue de ses conséquences sur l'évolution des génomes
Genomes are affected by conflicting selective regimes. This is particularly well illustrated by the concept of semi-permeable barriers to gene flow, as found in the hybrid zones literature. Some genes contribute to the prevention of mixing between differentiated genetic lineages, either because they are involved in adaptation to local environmental conditions, or because they are incompatible with alleles from other genetic lineages. Other parts of the genome are either neutral, or subjected to selection which tends to homogenize the genetic lineages. In the first part of this thesis, models of the evolution of reproductive isolation are presented to explain the isolation patterns observed in experimental hybridizing crosses between incipient species. Using standard models of Dobzhansky-Muller genetic incompatibilities, it is shown that the asymmetry and complexity of incompatibilities are not well explained by there being an “evolutionary sieve”, i.e. a different rate of accumulation between incompatibilities. A complementary approach to quantitative modeling (an extension of Fisher's Geometric Model) then clarifies which conditions of divergence between allopatric lines led to highly deleterious effects in hybrid genotypes. The relative importance of mean levels of fitness epistasis, the distribution of mutation sizes, and the way lineages adapt to new environmental conditions is discussed. The second part of this thesis takes advantage of technical advances in genomics to study the history of speciation and adaptation in a non-model species complex, Mytilus mussels. A statistical method of inferring speciation scenarios is presented. Results show that European mussels experienced a complex history of strict divergence followed by a period of periodic connectivity. In agreement with the concept of semi-permeable barriers to gene flow, it is shown that introgression rates are heterogeneous along the genome. Next, genome scans of differentiation were conducted between pairs of populations of the species complex. The analysis of genetic variation and allele genealogies on a small chromosomal scale allowed to reconstruct the evolutionary history of more than 1000 genomic regions. This analysis reveals that a major cause of intraspecific differentiation is the differential introgression of foreign alleles. Overall, this thesis shows not only that biogeography of speciation, i.e. the temporal and spatial patterns of gene flow, play a major role in our understanding of existing biodiversity, but also its amazing complexity and extent of its impact on genome evolution

Les Vagues de Chaleur Marines (VCM) ont augmenté en fréquence et en intensité depuis le siècle dernier. Les températures atmosphériques élevées sont un des facteurs d’apparition des VCM et sont souvent accompagnées d’une augmentation des activités récréatives sur le littoral, favorisant l’entrée dans les eaux de baignade des Filtres Ultra-Violets Organiques (FUVO) contenus dans les écrans solaires. Récemment, des effets néfastes ont été identifiés chez les organismes marins exposés aux VCM et aux FUVO. Cependant, les réponses écophysiologiques et comportementales lors d’expositions réalistes aux VCM et aux FUVO sont encore peu connues. L’objectif de cette thèse était d’étudier ces réponses chez deux espèces clés du littoral aux fonctions écologiques distinctes, la moule bleue (Mytilus edulis) et le mulet doré (Chelon auratus). Cette thèse a mis en évidence (1) qu’une VCM réaliste était à l’origine d’ajustements métaboliques ou comportementaux chez les 2 espèces, limitant in fine leur capacité de récupération après la VCM et (2) que le comportement des individus exposés à des concentrations environnementales de FUVO augmentait le risque de bioaccumuler ces polluants dans leurs tissus et d’induire des effets physiologiques délétères (observés chez C. auratus à l’échelle de la cellule et de l’organe). Ces travaux de thèse soulignent l’importance de considérer la capacité des individus à pallier un stress en mesurant leurs réponses à plusieurs échelles d’organisation afin d’avoir une vision globale des effets
Marine heatwaves (MHW) have increased in frequency and intensity since the last century. High atmospheric temperatures drive MHW and are often associated with an increase in coastal recreational activities, leading to the release of Organic Ultra Violet Filters (OUVF) present in sunscreens into bathing waters. Recently, adverse effects have been documented in marine organisms exposed to MHW and OUVF. However, little is known about the ecophysiological and behavioural responses to realistic exposures. The objective of this thesis was to study these responses on two key nearshore species with different ecological functions, the blue mussel (Mytilus edulis) and the golden grey mullet (Chelon auratus). This thesis demonstrated that (1) a realistic MHW caused metabolic or behavioural adjustments in both species, which in turn limited their ability to recover from the MHW and (2) that the behaviour of individuals exposed to environmental concentrations of OUVF increased the risk of bioaccumulating these pollutants in their tissues and induced adverse physiological effects (observed in C. auratus at the cellular and organ level). This work highlights the importance of considering the ability of individuals to cope with stress, by measuring their responses at several organizational levels in order to have a holistic view of the effects