Analysis of sexual phenotype and prezygotic fertility in natural populations of Fucus spiralis, F. vesiculosus (Fucaceae, Phaeophyceae) and their putative hybrids

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and hybridization is possible between taxa with contrasting mating systems, e.g. between the dioecious Fucus vesiculosus and the hermaphrodite F. spiralis. In the context of mating system evolution, we evaluated the potential consequences of hybridization by studying the variation in sexual phenotype and prezygotic fertility. Firstly, as a result of hybridization between the two sexual systems, gender variation may arise depending on the relative importance of genes with large versus small phenotypic effects. We thus qualitatively examined the extent of gender variation within and among individual hybrids in comparison with both parental species. Secondly, if hybridization breaks up co-adapted gene complexes, hybrid fertility may be reduced in comparison with both parental species. Therefore, we also quantified male and female prezygotic fertility in parental species and their hybrids in order to test for reduction in hybrid fitness. A total of 89 sexually mature individuals (20 F. spiralis, 40 F. vesiculosus, 10 hermaphrodite hybrids and 19 dioecious hybrids) were sampled in two geographically distant regions (France and Portugal) and six conceptacles per individual were observed. Within-individual variation was very restricted qualitatively – only one hybrid carried a conceptacle with a different sexual phenotype from the five others – as well as quantitatively. This suggests a simple genetic system for sex determination involving a few genes with major effects. In addition, analyses showed no significant decrease in hybrid fertility compared with parental species. Moreover, hybrids exhibited all sexual phenotypes, suggesting several generations of hybridization and backcrossing and, therefore, that hybrids are reproductively successful. Finally, the occurrence of sterile paraphyses in female and hermaphrodite individuals was interpreted as a relic of male function and suggests that, as in higher plants, evolution from hermaphroditism to dioecy may be the most parsimonious pathway

Temperature Effects on Gametophyte Life-History Traits and Geographic Distribution of Two Cryptic Kelp Species

A major determinant of the geographic distribution of a species is expected to be its physiological response to changing abiotic variables over its range. The range of a species often corresponds to the geographic extent of temperature regimes the organism can physiologically tolerate. Many species have very distinct life history stages that may exhibit different responses to environmental factors. In this study we emphasized the critical role of the haploid microscopic stage (gametophyte) of the life cycle to explain the difference of edge distribution of two related kelp species. Lessonia nigrescens was recently identified as two cryptic species occurring in parapatry along the Chilean coast: one located north and the other south of a biogeographic boundary at latitude 29–30°S. Six life history traits from microscopic stages were identified and estimated under five treatments of temperature in eight locations distributed along the Chilean coast in order to (1) estimate the role of temperature in the present distribution of the two cryptic L. nigrescens species, (2) compare marginal populations to central populations of the two cryptic species. In addition, we created a periodic matrix model to estimate the population growth rate (λ) at the five temperature treatments. Differential tolerance to temperature was demonstrated between the two species, with the gametophytes of the Northern species being more tolerant to higher temperatures than gametophytes from the south. Second, the two species exhibited different life history strategies with a shorter haploid phase in the Northern species contrasted with considerable vegetative growth in the Southern species haploid stage. These results provide strong ecological evidence for the differentiation process of the two cryptic species and show local adaptation of the life cycle at the range limits of the distribution. Ecological and evolutionary implications of these findings are discussed

Etude du cycle de reproduction et de la diversité genetique spatio-temporelle chez le dinoflagelle toxique alexandrium minutum

Alexandrium minutum est un dinoflagellé à l origine d efflorescences toxiques récurrentes le long des côtes bretonnes. Originaire de Méditerranée, cette espèce a progressivement envahi l Europe. L objectif de ce travail était d étudier les processus pouvant influencer la diversité génétique des populations d A. minutum. Tout d abord, des expériences que nous avons réalisées montrent que la rencontre des gamètes suit un processus complexe où les fusions ne sont pas régies par un système bipolaire. Ce qui pourrait expliquer la forte diversité observée au sein des efflorescences. En effet, l utilisation des microsatellites a permis de révéler une forte diversité génétique et génotypique. La reproduction sexuée chez cette espèce serait donc prédominante. L étude de la variabilité génétique spatiotemporelle au cours des efflorescences pendant deux années consécutives dans les estuaires de Penzé et de Rance révèle des différenciations génétiques significatives aux deux échelles. Ces résultats indiquent que les populations d A. minutum le long des côtes bretonnes sont isolées génétiquement mais aussi que leur composition génétique évolue au cours de la saison. Les traits d histoire de vie de cette espèce (production de kystes sexués) pourraient expliquer cette dynamique spatio-temporelle en renforçant la différenciation génétique entre estuaires. Les kystes pourraient constituer une réserve de génotypes, leur présence en grand nombre pourrait par un effet de tampon génétique et de compétition limiter l arrivée de nouveaux migrants dans ces estuaires. Ces résultats fournissent des paramètres essentiels pour la gestion des milieux côtiers menacés par les algues toxiques.Alexandrium minutum is a dinoflagellate producing recurrent toxic blooms along the French Atlantic coast. Originally from the Mediterranean, this species has gradually invaded the European coasts. In this study we examined the processes that may affect population genetic diversity of A. minutum. We made crossing experiments to determine its reproductive system. Then we used molecular tools to determine the importance of sexual reproduction in natural populations. Finally, we studied the genetic variability of annual blooms for two consecutive years in Penzé and Rance estuaries. Crossing experiments showed that gametes recognition in this species is not a bipolar system but involves different mating types. Using microsatellite markers, we found that blooms have a high genetic and genotypic diversity suggesting that clonal reproduction is not a dominant process during bloom period. The spatio-temporal genetic analyses showed significant differentiation at both spatial and temporal scales and indicates a restricted gene flow between the two sites. The genetic differentiation between estuaries could also be closely linked to the life history traits. Indeed, the rapid development of blooms in a new site, followed by the formation of a large number of cysts accumulated in estuaries could be a particular system characterized by high genetic buffer and limiting arrival of immigrants by competition. Finally, our results suggest that the toxic blooms observed in Rance, in the Morlaix Bay and Brest estuaries correspond to different introductions processes.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

A brief history of speciation research at the Station Biologique de Roscoff (1872-2022)

International audienceThe Station Biologique de Roscoff is celebrating its 150th anniversary. The occasion to take a break, to look back on the research done so far. Here we are interested in the origin of species. How does reproductive isolation evolve? How do barrier mechanisms appear and develop, and, accumulating, give rise to new species? These questions have been addressed in various ways at the Station biologique de Roscoff, in the framework of research projects that have as their most recent common ancestor the pioneering work of Georges Teissier in population genetics. Leaning on the soft or rocky substrates of the Roscoff coasts, with their feet in the water, Teissier and his colleagues and students gave a decisive impulse to French evolutionary biology. The mystery of the origin of species has since been the subject of various programs focused mainly on the evolution of marine algae and invertebrates. Some of these programs have been interested in describing the diversity and spatial distribution of species, focusing in particular on hybridization and gene flow at different spatial scales, across the foreshore, along the coasts, or between hydrothermal vents on an ocean scale. Another part of this work has sought to identify the mechanisms of reproductive isolation between species and their genetic basis. We retrace here the progress of these programs carried out at the station biologique de Roscoff since its foundation

Diversité génétique et délimitation d'espèces par des approches conjointes de barcoding et de génétique des populations (application à l'identification d'espèces d'algues marines nouvellement cultivées)

L identification de certaines espèces d algues d après leurs caractéristiques morphologiques reste encore aujourd hui problématique en raison notamment d une forte plasticité phénotypique ou de phénomènes de convergence. Je me suis intéressé à l utilisation de différents marqueurs moléculaires dans un but taxonomique. L objectif était plus précisément de caractériser et d étudier la diversité génétique de plusieurs espèces d algues marines cultivables d intérêts économiques. Dans une première partie, j ai utilisé une approche de type barcoding multilocus afin de trouver les caractères génétiques spécifiques indispensables pour assurer la traçabilité des produits dans l industrie des algues par une approche RFLP. La seconde partie a été consacrée à étudier la délimitation d espèces au sein d un genre d algues brunes Pylaiella. Notre étude montre la présence de deux espèces cryptiques présentant un décalage saisonnier. L utilisation de marqueurs de type microsatellite révèlent des flux de gènes limités entre ces deux entités. Dans une troisième partie l étude basée sur l analyse des séquences cox1 et rbcL dans le genre Polysiphonia a permis de mettre en évidence la présence de l algue introduite Polysiphonia morrowii Harvey. Enfin, la comparaison de la diversité haplotypique entre aire native supposée et aires d introduction révèle une diversité génétique relativement élevée dans les zones d introduction suggérant de multiples événements d introduction. Ces différents résultats soulignent l importance d approches moléculaires et intégratives pour l identification et la délimitation d espèces, notamment dans un contexte de traçabilité dans le milieu industriel des alguesPARIS-BIUSJ-Biologie recherche (751052107) / SudocROSCOFF-Observ.Océanol. (292393008) / SudocSudocFranceF

Management and conservation of the kelp species

Marine protected areas (MPAs) have been depicted as a useful tool for improving fishery management and protecting biodiversity. For example, by acting as source populations, MPAs may provide a spillover of adults/propagules, enhancing recruitment to surrounding, non-protected waters. However, such positive effect will depend on how a MPAs design matches population biology and dispersal abilities of the target species. High levels of intraspecific genetic diversity without pronounced structure have been found in many marine organisms over large spatial scales (from hundreds to thousands kilometres) but do not hold for other ecologically and economically important species such as coral reef fishes, seagrasses and kelps. In particular, the limited potential for dispersal of many macroalgae suggests the occurrence of self-sustaining, “closed” populations that contrast with the “open” populations of many fishes and invertebrates. Consequently, the high resilience of fish/invertebrate populations cannot be generalized to the whole marine realm. In the present work, we use genetic tools to explore the role of the MPA Parc naturel marin d’Iroise in the management of the emblematic kelp Laminaria digitata. While kelps have received much more scientific attention than any other seaweed group, there is still critical baseline knowledge which needs to be addressed for their effective management. Our genetic survey of 12 L. digitata populations along the Brittany coast, four of them located within the boundaries of the Parc naturel marin d’Iroise, allowed us to assess the conservation value of these kelp populations. In particular, classical genetic metrics as well as more recent clustering approaches were used to identify and characterize Management Units. Moreover, assignment tests were employed to determine contemporary migration events and source/sink populations. Our results show that populations within this MPA have high conservation value. However, we also identify other populations of conservation interest

Reproduction at the range limits of laminariales at the chilean and european coasts

Le développement, la reproduction et la survie d un organisme, dépendent de son environnement physique et/ou écologique. La sélection en faveur de certains traits d histoire de vie découle donc de la stabilité de l environnement (i.e. reproduction sexuée versus asexuée). La stratégie de reproduction d une espèce est par conséquent susceptible de se modifier en fonction des changements environnementaux, pouvant survenir en limite d aire de distribution qui se caractérisent par des fluctuations abiotiques plus importantes. Les grandes algues brunes (Phaeophyceae, Laminariales) sont des espèces structurant les communautés benthiques marines. Elles présentent un cycle de reproduction hétéromorphe avec alternance de phase haploïde microscopique (gamétophyte) et de phase diploïde macroscopique (sporophyte). Les connaissances sur la biologie et la distribution géographique de la plupart de ces espèces n étaient basées jusqu à présent que sur l étude des sporophytes. Mes travaux de thèse ont permis de mettre en évidence l importance de ces gamétophytes dans le maintien des populations, en comparant les modes de reproduction de trois espèces de laminaires. Les résultats suggèrent que le déterminisme du sexe est principalement génétique et que l effet de la température de l eau de mer sur la phase microscopique peut expliquer les distributions géographiques de certaines espèces. Par ailleurs, différents stratégies reproductives ont été observées au sein et entre espèces suggérant l existence de phénomènes d adaptations locales. En particulier, en limite d aire de distribution des espèces, nos résultats montrent l existence de la parthénogenèse géographique.PARIS-BIUSJ-Physique recherche (751052113) / SudocROSCOFF-Observ.Océanol. (292393008) / SudocSudocFranceChileFRC

First record of the invasive red alga Polysiphonia morrowii Harvey (Rhodomelaceae, Rhodophyta) on the Patagonian shores of the Southwestern Atlantic

International audienceSeaweed invasions are recognized as one of the major threats to biological diversity and coastal resources. Nevertheless, the number of introduced macroalgae has been underestimated due to the increasing number of cryptic invasions. Polysiphonia morrowii is native to the North Pacific and several cryptic introductions of this species have been reported over the past decade. In this study, we recorded the presence of the invasive P. morrowii in the Southwestern Atlantic (Patagonia Argentina) using a morphological and molecular approach for the identification at species level. Polysiphonia morrowii specimens from Argentina showed no morphological differences from members of invasive populations in France. We found two different haplotypes, suggesting that P. morrowii was probably introduced into this area by multiple introduction events. The increasing number of shipping and aquaculture activities worldwide and the ability of this species to be a successful invader suggest that P. morrowii is likely to be a cosmopolitan invasive species and that further management planning is required for its early detection and control

Temporal genomics help in deciphering neutral and adaptive patterns in the contemporary evolution of kelp populations

International audienceThe impact of climate change on populations will be contingent upon their contemporary adaptive evolution. In this study, we investigated the contemporary evolution of four populations of the cold-water kelp Laminaria digitata by analysing their spatial and temporal genomic variation using ddRAD-sequencing. These populations were sampled from the center to the southern margin of its north-eastern Atlantic distribution at two-time points, spanning at least two generations. Through genome scans for local adaptation at a single time point, we identified candidate loci that showed clinal variation correlated with changes in sea surface temperature (SST) along latitudinal gradients. This finding suggests that SST may drive the adaptive response of these kelp populations, although factors such as species' demographic history should also be considered. Additionally, we performed a simulation approach to distinguish the effect of selection from genetic drift in allele frequency changes over time. This enabled the detection of loci in the southernmost population that exhibited temporal differentiation beyond what would be expected from genetic drift alone: these are candidate loci which could have evolved under selection over time. In contrast, we did not detect any outlier locus based on temporal differentiation in the population from the North Sea, which also displayed low and decreasing levels of genetic diversity. The diverse evolutionary scenarios observed among populations can be attributed to variations in the prevalence of selection relative to genetic drift across different environments. Therefore, our study highlights the potential of temporal genomics to offer valuable insights into the contemporary evolution of marine foundation species facing climate change