Browsing by Author "Billard, E."
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- Analysis of sexual phenotype and prezygotic fertility in natural populations of Fucus spiralis, F. vesiculosus (Fucaceae, Phaeophyceae) and their putative hybridsPublication . Billard, E.; Serrão, Ester; Pearson, G. A.; Engel, C. R.; Destombe, C.; Valero, MyriamIn 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.
- Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North AtlanticPublication . Coyer, J. A.; Hoarau, G.; Costa, J. F.; Hogerdijk, B.; Serrão, Ester; Billard, E.; Valero, Myriam; Pearson, G. A.; Olsen, J. L.We examined 733 individuals of Fucusspiralis from 21 locations and 1093 Fucusvesiculosus individuals from 37 locations throughout their northern hemisphere ranges using nuclear and mitochondrial markers. Three genetic entities of F. spiralis were recovered. In northern and sympatric populations, the presence of "F. spiralis Low" in the mid-intertidal and "F. spiralis High" in the high-intertidal was confirmed and both co-occurred with the sister species F. vesiculosus. The third and newly-discovered entity, "F. spiralis South", was present mainly in the southern range, where it did not co-occur with F. vesiculosus. The South entity diverged early in allopatry, then hybridized with F. vesiculosus in sympatry to produce F. spiralis Low. Ongoing parallel evolution of F. spiralis Low and F. spiralis High is most likely due to habitat preference/local selection and maintained by preferentially selfing reproductive strategies. Contemporary populations of F. spiralis throughout the North Atlantic stem from a glacial refugium around Brittany involving F. spiralis High; F. spiralis South was probably unaffected by glacial episodes. Exponential population expansion for F. vesiculosus began during the Cromer and/Holstein interglacial period (300,000-200,000 yrs BP). Following the last glacial maximum (30,000-22,000 yrs BP), a single mtDNA haplotype from a glacial refugium in SW Ireland colonized Scandinavia, the Central Atlantic islands, and the W Atlantic.
- Evolution of mating systems and their implication in the processes of speciation and hybridization in brown algae of the genus FucusPublication . Billard, E.; Serrão, Ester; Valero, M.Chez les algues brunes du genre Fucus, le caractère dioécie/hermaphrodisme a évolué plusieurs fois et l’hybridation est possible entre taxa possédant des systèmes de reproduction contrastés. Ces singularités en font un excellent modèle pour étudier l’évolution des systèmes de reproduction aussi bien à l’échelle macro que micro-évolutive. Une approche phylogénétique basée sur l’analyse de séquences chloroplastiques démontre que, comme chez les plantes supérieures, l’hermaphrodisme est ancestral chez ces algues. Cependant, les taxa F. vesiculosus, F. spiralis et F. ceranoides sont compris dans un râteau irrésolu, mettant en question leur statut d’espèce. Par l’utilisation de marqueurs du flux génique nous avons démontré que les trois espèces étaient bien isolées reproductivement quoique incomplètement. Afin d’étudier l’importance de la barrière aux flux géniques, nous avons concentré notre analyse à l’échelle d’un estran, zone de transition entre F. vesiculosus et F. spiralis. Différentes approches, alliant génétique et biologie des populations ont été utilisées. Comme attendu selon les modèles écologiques de l’évolution des systèmes de reproduction, l’espèce hermaphrodite montre un très faible ratio sperme/ovule tandis qu’une réallocation des ressources vers la fonction mâle est constatée chez l’espèce dioïque. Nos résultats démontrent que l’hybridation est fortement limitée spatialement par de faibles capacités de dispersion et un fort taux d’autofécondation chez F. spiralis. Elle est due au sperme F. vesiculosus fécondant les ovules de F. spiralis. Ces résultats apportent de nouvelles preuves de l’importance des régimes de reproduction lors du processus de spéciation.
- Fucus vesiculosus and spiralis species complex: A nested model of local adaptation at the shore levelPublication . Billard, E.; Serrão, Ester; Pearson, G. A.; Destombe, C.; Valero, MyriamIntertidal rocky shores provide classic examples of habitat-driven divergent selection. We show that the species complex Fucus vesiculosus L./F. spiralis L. is composed of 3 distinct genetic entities that have evolved along different time scales. Using assignment tests based on microsatellite markers and performed on randomly sampled individuals in 2 separate geographic regions (Portugal and France), we reveal that F. spiralis consists of 2 genetic entities that have distinct vertical distributional patterns along the intertidal gradient of selective pressures. Individuals assigned to the cluster found higher on the shore are also morphologically different. They are smaller and bushy, with dichotomous ramifications and no sterile rime around receptacles. Patterns of genetic divergence suggest different times and pathways to reproductive isolation. Divergence between F. vesiculosus and the F. spiralis complex seems to have occurred first, coinciding with divergence in reproductive mode; dioecy versus selfing hermaphroditism. Later, in the hermaphroditic lineage, parallel evolution of 2 co-occurring genetic clusters may have been driven by natural selection and facilitated by high selfing rates in the F. spiralis complex.
- Genetic isolation between three closely related taxa: fucus vesiculosus, F. spiralis, and F. ceranoides (Phaophyceae)Publication . Billard, E.; Daguin, C.; Pearson, G. A.; Serrão, Ester; Engel, C. R.; Valero, MyriamAll traditional markers, both phenotypic and phylogenetic, have failed to discriminate between the taxa composing the Fucus vesiculosus L., F. spiralis L., and F. ceranoides L. species complex, particularly in Brittany (France), so we used five microsatellite markers to compare the allelic frequencies of populations of the three taxa in this region. The aim of this study was to assess whether the different populations were grouped according to their geographical location, their habitat (open coast versus estuary), or their a priori taxonomic assignment. Species-specific alleles were identified at one locus, demonstrating the utility of microsatellite markers for recognizing the three taxa in Brittany. Moreover, our results clearly support the separation of F. vesiculosus, F. spiralis, and F. ceranoides into distinct species, independently of geography. We also identified genetic differentiation between estuarine and coastal populations of F. vesiculosus.