Emmanuelle Billard | Universidade do Porto (original) (raw)

Papers by Emmanuelle Billard

Research paper thumbnail of The Size Advantage Model of Sex Allocation in the Protandrous Sex-Changer Crepidula fornicata : Role of the Mating System, Sperm Storage, and Male Mobility

The American Naturalist, 2015

Sequential hermaphroditism is adaptive when the reproductive value of an individual varies with s... more Sequential hermaphroditism is adaptive when the reproductive value of an individual varies with size or age, and this relationship differs between males and females. In this case, theory shows that the lifetime reproductive output of an individual is increased by changing sex (a hypothesis referred to as the size-advantage model). Sex-linked differences in size-fitness curves can stem from differential costs of reproduction, the mating system, and differences in growth and mortality between sexes. Detailed empirical data is required to disentangle the relative roles of each of these factors within the theory. Quantitative data are also needed to explore the role of sperm storage, which has not yet been considered with sequential hermaphrodites. Using experimental rearing and paternity assignment, we report relationships between size and reproductive success of Crepidula fornicata, a protandrous (male-first) gastropod. Male reproductive success increased with size due to the polygamous system and stacking behavior of the species, but females nonetheless had greater reproductive success than males of the same size, in agreement with the size-advantage theory. Sperm storage appeared to be a critical determinant of success for both sexes, and modeling the effect of sperm storage showed that it could potentially accelerate sex change in protandrous species.

Research paper thumbnail of When is it worth being a self-compatible hermaphrodite? Context-dependent effects of self-pollination on female advantage in gynodioecious Silene nutans

Ecology and Evolution, 2015

In gynodioecious plant species with nuclear-cytoplasmic sex determination, females and hermaphrod... more In gynodioecious plant species with nuclear-cytoplasmic sex determination, females and hermaphrodites plants can coexist whenever female have higher seed fitness than hermaphrodites. Although the effect of self fertilization on seed fitness in hermaphrodites has been considered theoretically, this effect is far from intuitive, because it can either increase the relative seed fitness of the females (if it leads hermaphrodites to produce inbred, low quality offspring) or decrease it (if it provides reproductive assurance to hermaphrodites). Hence, empirical investigation is needed to document whether relative seed fitness varies with whether pollen is or is not limiting to seed production. In the current study, we measured fruit set and seed production in both females and hermaphrodites and the selfing rate in hermaphrodites in two experimental patches that differed in sex ratios in the gynodioecious plant Silene nutans. We found an impact of plant gender, patch, and their interaction, with females suffering from stronger pollen limitation when locally frequent. In the most pollen-limited situation, the selfing rate of hermaphrodites increased and provided hermaphrodites with a type of reproductive assurance that is not available to females. By integrating both the beneficial (reproductive assurance) and costly effects (through inbreeding depression) of self-pollination, we showed that whether females did or did not exhibit higher seed fitness depended on the degree of pollen limitation on seed production.

Research paper thumbnail of Genetic isolation between three closely related taxa: Fucus vesiculosus, F-Spiralis, and F-Ceranoides (Phaophyceae

Journal of Phycology, 2005

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between th... more All 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.

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

European Journal of Phycology, 2005

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and... more 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.

Research paper thumbnail of Deep genetic divergence between austral populations of the red alga Gigartina skottsbergii reveals a cryptic species endemic to the Antarctic continent

Polar Biology, 2015

The almost complete isolation of Antarctica after the intensification the Antarctic circumpolar c... more The almost complete isolation of Antarctica after the intensification the Antarctic circumpolar current (ACC) during the middle-Miocene has been challenged by recent molecular data showing the existence of allelic exchange across the ACC. For organisms present on both sides of the ACC, two hypotheses have then been discussed to explain the origin of the Antarctic populations: (1) They correspond to recent immigrants from adjacent continents, or (2) they have evolved in situ and have survived the dramatic effects of the last Quaternary glaciations in this region. The red algae Gigartina skottsbergii presents a disjoint distribution and is reported in both Antarctica and southern South America, a distribution pattern that largely exceeds its dispersal capacity. Mitochondrial sequences of the intergenic region Cox2-3 (n = 233) and partial chloroplastic RuBisCo large subunit gene (n = 26) sequences were obtained for individuals from the Chilean sub-Antarctic ecoregion and Antarctic Peninsula localities. The results strongly support the persistence of populations on each side of the Drake Passage during glacial periods and the existence of dispersal barrier due to the ACC. On both sides of the ACC, the last Quaternary glaciations have induced strong bottlenecks that were followed by rapid colonization events.

Research paper thumbnail of Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

Marine Ecology Progress Series, 2010

Intertidal rocky shores provide classic examples of habitat-driven divergent selection. We show t... more Intertidal 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.

Research paper thumbnail of How much better are females? The occurrence of female advantage, its proximal causes and its variation within and among gynodioecious species

Annals of Botany, 2012

Background Gynodioecy is a reproductive system of interest for evolutionary biologists, as it pos... more Background Gynodioecy is a reproductive system of interest for evolutionary biologists, as it poses the question of how females can be maintained while competing with hermaphrodites that possess both male and female functions. One necessary condition for the ...

Research paper thumbnail of Conservation and polymorphism of mitochondrial intergenic sequences in brown algae (Phaeophyceae)

European Journal of …, 2008

... The Baltic Sea as a model system for studying postglacial colonization and ecological differe... more ... The Baltic Sea as a model system for studying postglacial colonization and ecological differentiation, exemplified by the red alga Ceramium tenuicorne ... A molecular re-examination of speciation in the intertidal red alga Mastocarpus stellatus (Gigartinales, Rhodophyta) in Europe ...

Research paper thumbnail of Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

Intertidal rocky shores provide classic examples of habitat-driven divergent selection. We show t... more Intertidal 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.

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

European Journal of Phycology, 2005

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and... more 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.

Research paper thumbnail of Genetic isolation between three closely related taxa: Fucus vesiculosus, F-Spiralis, and F-Ceranoides (Phaophyceae

Journal of Phycology, 2005

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between th... more All 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.

Research paper thumbnail of Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/ F. vesiculosus species complex in the North Atlantic

Molecular Phylogenetics and Evolution, 2011

Research paper thumbnail of GENETIC ISOLATION BETWEEN THREE CLOSELY RELATED TAXA: FUCUS

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between th... more All 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.

Research paper thumbnail of The Size Advantage Model of Sex Allocation in the Protandrous Sex-Changer Crepidula fornicata : Role of the Mating System, Sperm Storage, and Male Mobility

The American Naturalist, 2015

Sequential hermaphroditism is adaptive when the reproductive value of an individual varies with s... more Sequential hermaphroditism is adaptive when the reproductive value of an individual varies with size or age, and this relationship differs between males and females. In this case, theory shows that the lifetime reproductive output of an individual is increased by changing sex (a hypothesis referred to as the size-advantage model). Sex-linked differences in size-fitness curves can stem from differential costs of reproduction, the mating system, and differences in growth and mortality between sexes. Detailed empirical data is required to disentangle the relative roles of each of these factors within the theory. Quantitative data are also needed to explore the role of sperm storage, which has not yet been considered with sequential hermaphrodites. Using experimental rearing and paternity assignment, we report relationships between size and reproductive success of Crepidula fornicata, a protandrous (male-first) gastropod. Male reproductive success increased with size due to the polygamous system and stacking behavior of the species, but females nonetheless had greater reproductive success than males of the same size, in agreement with the size-advantage theory. Sperm storage appeared to be a critical determinant of success for both sexes, and modeling the effect of sperm storage showed that it could potentially accelerate sex change in protandrous species.

Research paper thumbnail of When is it worth being a self-compatible hermaphrodite? Context-dependent effects of self-pollination on female advantage in gynodioecious Silene nutans

Ecology and Evolution, 2015

In gynodioecious plant species with nuclear-cytoplasmic sex determination, females and hermaphrod... more In gynodioecious plant species with nuclear-cytoplasmic sex determination, females and hermaphrodites plants can coexist whenever female have higher seed fitness than hermaphrodites. Although the effect of self fertilization on seed fitness in hermaphrodites has been considered theoretically, this effect is far from intuitive, because it can either increase the relative seed fitness of the females (if it leads hermaphrodites to produce inbred, low quality offspring) or decrease it (if it provides reproductive assurance to hermaphrodites). Hence, empirical investigation is needed to document whether relative seed fitness varies with whether pollen is or is not limiting to seed production. In the current study, we measured fruit set and seed production in both females and hermaphrodites and the selfing rate in hermaphrodites in two experimental patches that differed in sex ratios in the gynodioecious plant Silene nutans. We found an impact of plant gender, patch, and their interaction, with females suffering from stronger pollen limitation when locally frequent. In the most pollen-limited situation, the selfing rate of hermaphrodites increased and provided hermaphrodites with a type of reproductive assurance that is not available to females. By integrating both the beneficial (reproductive assurance) and costly effects (through inbreeding depression) of self-pollination, we showed that whether females did or did not exhibit higher seed fitness depended on the degree of pollen limitation on seed production.

Research paper thumbnail of Genetic isolation between three closely related taxa: Fucus vesiculosus, F-Spiralis, and F-Ceranoides (Phaophyceae

Journal of Phycology, 2005

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between th... more All 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.

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

European Journal of Phycology, 2005

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and... more 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.

Research paper thumbnail of Deep genetic divergence between austral populations of the red alga Gigartina skottsbergii reveals a cryptic species endemic to the Antarctic continent

Polar Biology, 2015

The almost complete isolation of Antarctica after the intensification the Antarctic circumpolar c... more The almost complete isolation of Antarctica after the intensification the Antarctic circumpolar current (ACC) during the middle-Miocene has been challenged by recent molecular data showing the existence of allelic exchange across the ACC. For organisms present on both sides of the ACC, two hypotheses have then been discussed to explain the origin of the Antarctic populations: (1) They correspond to recent immigrants from adjacent continents, or (2) they have evolved in situ and have survived the dramatic effects of the last Quaternary glaciations in this region. The red algae Gigartina skottsbergii presents a disjoint distribution and is reported in both Antarctica and southern South America, a distribution pattern that largely exceeds its dispersal capacity. Mitochondrial sequences of the intergenic region Cox2-3 (n = 233) and partial chloroplastic RuBisCo large subunit gene (n = 26) sequences were obtained for individuals from the Chilean sub-Antarctic ecoregion and Antarctic Peninsula localities. The results strongly support the persistence of populations on each side of the Drake Passage during glacial periods and the existence of dispersal barrier due to the ACC. On both sides of the ACC, the last Quaternary glaciations have induced strong bottlenecks that were followed by rapid colonization events.

Research paper thumbnail of Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

Marine Ecology Progress Series, 2010

Intertidal rocky shores provide classic examples of habitat-driven divergent selection. We show t... more Intertidal 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.

Research paper thumbnail of How much better are females? The occurrence of female advantage, its proximal causes and its variation within and among gynodioecious species

Annals of Botany, 2012

Background Gynodioecy is a reproductive system of interest for evolutionary biologists, as it pos... more Background Gynodioecy is a reproductive system of interest for evolutionary biologists, as it poses the question of how females can be maintained while competing with hermaphrodites that possess both male and female functions. One necessary condition for the ...

Research paper thumbnail of Conservation and polymorphism of mitochondrial intergenic sequences in brown algae (Phaeophyceae)

European Journal of …, 2008

... The Baltic Sea as a model system for studying postglacial colonization and ecological differe... more ... The Baltic Sea as a model system for studying postglacial colonization and ecological differentiation, exemplified by the red alga Ceramium tenuicorne ... A molecular re-examination of speciation in the intertidal red alga Mastocarpus stellatus (Gigartinales, Rhodophyta) in Europe ...

Research paper thumbnail of Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

Intertidal rocky shores provide classic examples of habitat-driven divergent selection. We show t... more Intertidal 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.

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

European Journal of Phycology, 2005

In the genus Fucus, the character dioecy/hermaphroditism has undergone multiple state changes and... more 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.

Research paper thumbnail of Genetic isolation between three closely related taxa: Fucus vesiculosus, F-Spiralis, and F-Ceranoides (Phaophyceae

Journal of Phycology, 2005

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between th... more All 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.

Research paper thumbnail of Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/ F. vesiculosus species complex in the North Atlantic

Molecular Phylogenetics and Evolution, 2011

Research paper thumbnail of GENETIC ISOLATION BETWEEN THREE CLOSELY RELATED TAXA: FUCUS

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between th... more All 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.