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

Male gametophyte fragmentation in <i>Laminaria digitata</i>: a life history strategy to enhance reproductive success

An understanding of the life history of Laminaria digitata is crucial to implementing efficient management practices that can ensure the persistence of the kelp forest. L. digitata shows an obligate haplo-diplont heteromorphic life cycle with alternation of a large sporophyte and dioecious microscopic gametophytes. The study of growth and reproduction in culture conditions demonstrated different strategies in male and female gametophytes: Males grew vegetatively and reproduced simultaneously, whereas females stopped growing after reproduction. In addition, we demonstrated that males were able to fragment to give new gametophyte individuals. These results suggest that male and female gametophytes have developed two contrasting reproductive strategies with semelparous females and iteroparous males enhancing the reproductive success of the species

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

Cryptic introduction of the red alga Polysiphonia morrowii Harvey (Rhodomelaceae, Rhodophyta) in the North Atlantic Ocean highlighted by a DNA barcoding approach

International audienceMacroalgae are prone to be introduced outside of their autochthonous area; however, the difficulty to unequivocally identify them based on morpho-anatomical features, mainly due to the lack of diagnostic characters, often hampered the rapid detection of exogenous species. In the present study, we document that the Polysiphonia species that dominates, during spring, the high intertidal level in Brittany is Polysiphonia morrowii. We demonstrated the presence of this alien species in the North Eastern Atlantic in light of molecular sequences. This species originally from the Northwest Pacific Ocean has already been reported as introduced in Chile and New Zealand on a molecular ground and has been suspected in North Sea and Mediterranean Sea based on morpho-anatomical ground. Among the 105 individuals of P. morrowii collected along the coast of Brittany, three haplotypes were found suggesting several introduction events. In our opinion, the progression of this exogenous species, which has been so far undetected due to its morphological similarities with native species, should be further monitored

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