Stabilizing selection on nectar concentration in wild Petunia axillaris , as revealed by genetic analysis of pollen dispersal

Most animal-pollinated plants produce nectar as a pollinator reward. Despite the main role that nectar plays in plant-pollinator interactions, the impact of natural variation in nectar traits on realized male fitness is poorly known. Here, we assessed this relation for a wild Petunia axillaris population using paternity-based direct selection gradient analysis, which allowed us also to infer pollen dispersal patterns. Because male fecundity may depend on other traits which could be associated with nectar characteristics (i.e. volume and concentration), we also considered selection on other key reproductive traits. The analysis revealed that P. axillaris was a strict outcrosser, but that successful pollination occurred mainly among neighbours. Individual plants varied greatly in their male fecundity. Nectar concentration, a key feature of nectar that determines its profitability, was subjected to stabilizing selection. Selection through male function also affected corolla area (positive directional selection), corolla tube length (negative directional selection), and floral display size (stabilizing selection), but none of these traits were phenotypically correlated with nectar characteristics. Because nectar concentration affects the ability and foraging efficiency of different flower visitors to feed on nectar, stabilizing selection may reflect either the preference of the most effective pollinators, or antagonistic selection driven by pollinators and non-pollinating nectar consumers

Assortative mating and differential male mating success in an ash hybrid zone population

BACKGROUND: The structure and evolution of hybrid zones depend mainly on the relative importance of dispersal and local adaptation, and on the strength of assortative mating. Here, we study the influence of dispersal, temporal isolation, variability in phenotypic traits and parasite attacks on the male mating success of two parental species and hybrids by real-time pollen flow analysis. We focus on a hybrid zone population between the two closely related ash species Fraxinus excelsior L. (common ash) and F. angustifolia Vahl (narrow-leaved ash), which is composed of individuals of the two species and several hybrid types. This population is structured by flowering time: the F. excelsior individuals flower later than the F. angustifolia individuals, and the hybrid types flower in-between. Hybrids are scattered throughout the population, suggesting favorable conditions for their local adaptation. We estimate jointly the best-fitting dispersal kernel, the differences in male fecundity due to variation in phenotypic traits and level of parasite attack, and the strength of assortative mating due to differences in flowering phenology. In addition, we assess the effect of accounting for genotyping error on these estimations. RESULTS: We detected a very high pollen immigration rate and a fat-tailed dispersal kernel, counter-balanced by slight phenological assortative mating and short-distance pollen dispersal. Early intermediate flowering hybrids, which had the highest male mating success, showed optimal sex allocation and increased selfing rates. We detected asymmetry of gene flow, with early flowering trees participating more as pollen donors than late flowering trees. CONCLUSION: This study provides striking evidence that long-distance gene flow alone is not sufficient to counter-act the effects of assortative mating and selfing. Phenological assortative mating and short-distance dispersal can create temporal and spatial structuring that appears to maintain this hybrid population. The asymmetry of gene flow, with higher fertility and increased selfing, can potentially confer a selective advantage to early flowering hybrids in the zone. In the event of climate change, hybridization may provide a means for F. angustifolia to further extend its range at the expense of F. excelsior

Social transmission of reproductive behavior increases frequency of inherited disorders in a young-expanding population

The observation of high frequencies of certain inherited disorders in the population of Saguenay–Lac Saint Jean can be explained in terms of the variance and the correlation of effective family size (EFS) from one generation to the next. We have shown this effect by using the branching process approach with real demographic data. When variance of EFS is included in the model, despite its profound effect on mutant allele frequency, any mutant introduced in the population never reaches the known carrier frequencies (between 0.035 and 0.05). It is only when the EFS correlation between generations is introduced into the model that we can explain the rise of the mutant alleles. This correlation is described by a c parameter that reflects the dependency of children’s EFS on their parents’ EFS. The c parameter can be considered to reflect social transmission of demographic behavior. We show that such social transmission dramatically reduces the effective population size. This could explain particular distributions in allele frequencies and unusually high frequency of certain inherited disorders in some human populations

Post marital residence behaviours shape genetic variation in hunter-gatherer and agricultural populations from Central Africa

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Neutral Theory: From Complex Population History to Natural Selection and Sociocultural Phenomena in Human Populations

International audienceHere, we present a synthetic view on how Kimura's Neutral theory has helped us gaining insight on the different evolutionary forces that shape human evolution. We put this perspective in the frame of recent emerging challenges: the use of whole genome data for reconstructing population histories, natural selection on complex polygenic traits, and integrating cultural processes in human evolution

Inférence des processus démographiques passés à partir de différents marqueurs génétiques pour des populations humaines aux modes de vie contrastés

Reconstruire l histoire démographique de notre espèce est un défi pour de nombreuses disciplines. Notamment, l émergence de l agriculture et de l élevage au Néolithique est largement considérée par les archéologues et paléoanthropologues comme le déclencheur des grandes expansions démographiques. A l inverse, peu d études de génétique des populations ont détecté des traces d expansions néolithiques dans le polymorphisme génétique actuel, soulignant plutôt des expansions plus anciennes (Paléolithique moyen ou supérieur). Ici, nous avons inféré l histoire démographique de populations d Afrique et d Eurasie aux modes de vie contrastés, à l aide de plusieurs méthodes issues de la théorie de la coalescence appliquées à différents marqueurs génétiques. L analyse de séquences autosomales et mitochondriales révèle une première expansion au Paléolithique, excepté chez les ancêtres des chasseurs-cueilleurs actuels en Afrique. Grâce aux microsatellites autosomaux, nous démontrons également une deuxième phase d expansion plus récente, compatible avec la transition néolithique, chez les populations d agriculteurs sédentaires mais pas chez les populations d éleveurs nomades. Nous avons également montré que les processus de migration et d isolation peuvent influencer dans une certaine mesure les inférences démographiques pour certaines populations. Enfin des analyses sur données simulées nous ont permis de tester les méthodes utilisées et ont confirmé le fait que, dans le cas de deux expansions successives au cours du temps, les données de séquences tendront à nous renseigner sur l évènement le plus ancien tandis que les données microsatellites dévoileront l évènement le plus récent.Reconstructing the demographic History of human populations remains a strongly investigated issue in many disciplines. In particular, the transition from hunting and gathering to plant and animal domestication during the Neolithic period is widely assumed by paleoanthropologists and archeologists to have driven recent human population expansions. Conversely, although demographic changes leave footprints on genetic polymorphism, few population genetic studies have found traces of Neolithic expansions in the current repartition of human genetic diversity, pointing rather toward more ancient (i.e. Middle or Upper Paleolithic) expansions. Here, we inferred the demographic history of multiple African and Eurasian populations with contrasted life styles, using several coalescent-based methods applied to different types of genetic markers. The analyses on autosomal and mitochondrial sequences revealed a Paleolithic expansion event for most populations, except for the ancestors of contemporary African hunter-gatherers. Using autosomal microsatellites, we also inferred a more recent expansion event, likely concomitant with the Neolithic transition, in sedentary farmer but not in nomadic herder populations. We also found that, in some cases, isolation and migration patterns can have an impact on coalescent-based inferences. Finally, using simulated data, we confirmed the fact that, when two consecutive expansions occur, sequence data generally give information about the oldest one while microsatellite data can bring information about the most recent one.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Modélisation de l'impact de la sélection naturelle et culturelle sur la diversité génétique (cas de la transmission du succès reproducteur et des réseaux de gènes)

Les forces de sélection sont un des moteurs de l évolution de la diversité phénotypique et de la diversité génétique neutre et des zones codantes du génome. Cette sélection peut s appliquer sur des caractères transmis génétiquement ou culturellement. Le travail effectué s intéresse à ces deux processus de sélection. Nous avons étudié dans un premier temps les effets de la transmission intergénérationnelle de la fécondité sur la diversité génétique neutre puis dans un deuxième temps l impact de la sélection sur des phénotypes codés par des réseaux de gènes sur le polymorphisme de ces gènes.La transmission de la fécondité est un phénomène culturel ou génétique qui se caractérise par une corrélation positive entre la taille de fratrie d un individu et la taille de fratrie de ses enfants. Il a été observé tant dans des populations humaines qu animales. Nous montrons, par l outil de la modélisation, que ses effets et la possibilité de le détecter dépendent autant du type de données étudiées (génétiques ou généalogiques), que des différents types de transmission (uniparentale, biparentale). Nous montrons que d autres phénomènes, tels que l hétérogénéité du succès reproducteur des individus, peuvent fortement moduler son impact. Nous développons un certain nombre d outils permettant de détecter ce phénomène de transmission de la fécondité tant sur des données généalogiques que sur des données génétiques relevant de différents modèles mutationnels (microsatellite, séquences, SNPs) et de différents types de transmission (haploïde ou diploïde, lié au sexe ou non). Nous avons appliqué ces outils notamment à trois populations humaines du Cilento en Italie (généalogies et ADN mitochondrial), des données d Asie Centrale (chromosome Y) et des données HapMap (autosomes).La seconde partie de la thèse porte sur la modélisation de l action de la sélection naturelle sur des caractères codés par des réseaux de régulation et décrit l impact de ce type de sélection sur l évolution du phénotype et sur la diversité des gènes sous-jacents. Un phénotype est le résultat des interactions entre différents gènes et leurs produits. Nous montrons que la sélection sur ce phénotype va modifier l organisation du réseau de gènes ainsi que le niveau de polymorphisme des gènes du réseau. Par exemple, lorsque le phénotype optimal correspond à une expression médiane des gènes, les gènes les plus régulateurs vont être soumis à une plus forte perte de diversité. En revanche, si le phénotype optimal correspond à une expression très forte, ce sont les gènes les plus régulés qui vont être les plus contraints. Cette analyse a permis de montrer la complexité des relations entre sélection, réseaux de régulation, phénotypes et environnement.Selective forces are one of the major determinants of the evolution of phenotypic diversity and genetic diversity, in neutral and coding zones of the genome. Selection can occur on genetically - or culturally - transmitted traits. This thesis considers these two selective processes. First, we studied the effects of intergenerational fertility transmission on neutral genetic diversity. Second, we considered the impact of selection on phenotypes coded by a gene network and on the polymorphism of genes within the network.Fertility transmission is a cultural or genetic phenomenon, which is characterised by a positive correlation between the sibship size of an individual and that of its children. It was observed both in human and animal populations. Using a modelling approach, we show that its effects and the possibility to detect it depend both on the kind of studied data (genetic or genealogical data) and on the different kind of transmission (uniparental, biparental). We show that other phenomena, such as the heterogeneity of reproductive success between individuals, can affect its effects. We develop several tools allowing to infer this phenomenon of fertility transmission on genealogical data, as well as on genetic polymorphism data that follows different mutational models (microsatellites, sequences, SNPs) and different transmission modes (haploid or diploid, sex-linked or not). We applied in particular these tools to three human populations of the Cilento area in Italy (genealogical and mitochondrial DNA data), to Central Asian data (Y chromosome) and to HapMap data (autosomes).The second part of this thesis deals with the modelling of the action of natural selection on traits coded by regulation networks and describes the impact of such selection on the evolution of the phenotype and of the underlying genes. A given phenotype is the result of the interaction between different genes and their products. We show that phenotypic selection will modify the gene network organisation, as well as the level of polymorphism of the genes involved in the network. For example, when the optimal phenotype corresponds to an intermediate level of gene expression, the most regulatory genes will lose much of their diversity. Conversely, if the optimal phenotype corresponds to a very strong expression of the genes, it will be the most regulated genes that will be the most constrained. This analysis allowed us to show the complexity of the relations between selection, regulation networks, phenotypes and the environment.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF