1,720,984 research outputs found
Perenniality induces high inbreeding depression in self-fertilising species
No full textWhen predicting the fate and consequences of recurring deleterious mutationsin self-fertilising populations most models developed make the assumptionthat populations have discrete non-overlapping generations. This makesthem biologically irrelevant when considering perennial species with overlappinggenerations and where mating occurs independently of the age group.The few models studying the effect of perennial life-histories on the geneticproperties of populations in the presence of self-fertilisation have done soconsidering age-dependent selection. They find low levels of inbreeding depressionin perennial populations that do not explain empirical observations.Here we propose a simple deterministic model in continuous time with selectionat different fitness traits and feedback between population fitnessand size. We find that a perennial life-history can result in high levels ofinbreeding depression in spite of inbreeding, due to higher frequencies of heterozygousindividuals at the adult stage. We also propose that there may bedemographic advantages for self-fertilisation that are independent of reproductivesuccess
Mort et stérilité avec un zeste de suicide évolutif : Interaction entre mutations délétères et taille de population, et l’évolution de l’autofécondation
No full textLa présence des mutations délétères a favorisé l'évolution de mécanismes, au niveau cellulaire et au niveau des organismes (e.g. les régimes de reproduction), permettant de diminuer leurs effets négatifs. Au cours de cette thèse nous avons étudié leur impact sur la taille des populations à travers des modèles tenant compte de l'interaction entre la démographie et la sélection, cette interaction étant souvent mise de coté dans les modèles conventionnels de génétique des populations. Dans un contexte déterministe à un seul locus des mutations somatiques et gamétiques influencent la taille et le fardeau génétique des populations (ces derniers étant dépendants du moment d’expression des mutations dans le cycle de vie). Nos modèles stochastiques avec un grand nombre de locus indiquent que la viabilité des populations dépend des paramètres démographiques et génétiques (taux de mutation, effet délétère des mutations). L'autofécondation est généralement avantageuse, augmentant la taille et la viabilité des populations, mais lorsque les mutations sont de faible effet un régime d'autogamie stricte mène à l'extinction par fonte mutationelle. En permettant l'évolution de l'autofécondation à partir d'une population allogame nous observons des cas de suicide évolutif où les populations évoluent vers l'autogamie stricte et s'éteignent, ce qui pourrait expliquer les taux d’extinctions élevés des espèces auto-fécondantes comparées aux allo-fécondantes. Ces modèles prédisent que la taille des populations pourrait être une conséquence et non une cause de leurs propriétés génétiques, appuyant sur l’importance de prendre en compte leur interaction dans l'étude de l'évolution des populations.As the ultimate source of genetic variation, mutation has the inconvenience of introducing deleterious mutations. These mutations shape the evolution of species, from genetic mechanisms on the cellular level to reproductive systems, which lessen their effects on fitness. In this thesis we explore how these mutations influence population size by allowing the interaction between population size and selection, which has been little explored in conventional population genetics models. In a deterministic context with a single locus, germ-line and somatic mutations influence population size and the mutation load, both which depend on the timing of the expression of these mutations. Multi-locus individual based models show that population viability depends on the demographic properties and on the rate of introduction and impact of mutations. Though self-fertilisation generally increases population viability, strictly self-fertilising populations go extinct due to mutational meltdown when mutations are of small effect. When selfing is allowed to evolve from an outcrossing reproductive regime, there are cases of evolutionary suicide where strict selfing evolves and leads to extinction. We predict that the genetic properties of populations may not be a consequence but a cause of population size. We have emphasized the importance of taking the demographic consequences of deleterious mutations into account when studying the evolution of populations, as in the case of the evolution of self-fertilisation where the previously undetected evolutionary suicide was observed. This result may explain the observed higher extinction rates in selfing compared to outcrossing species
Hide and seek: hidden genetic variance contributing to the adaptive potential of selfing populations
No full textStanding genetic variation is considered a major contributor to the adaptive potential of species. The low heritable genetic variation observed in self-fertilising populations has led to the hypothesis that species with this particular mating system would be less likely to adapt. However, a non-negligible amount of cryptic genetic variation for polygenic traits, accumulated through negative linkage disequilibrium, could prove to be an important source of standing variation in self-fertilising species. Using a classical quantitative genetics model, we demonstrate that selfing populations are better able to store cryptic genetic variance than outcrossing populations, notably due to their lower recombination rate. Following a shift in the environment, this hidden diversity can be partially released, increasing the additive variance and adaptive potential of selfing populations. In such conditions, even though the process of adaptation itself is mating system dependant, selfers reach levels of fitness that are equal to or higher than outcrossing populations within a few generations. Outcrossing populations respond better to selection for the new optimum, but they maintain more genetic diversity resulting in a higher genetic load. In selfing populations, genetic diversity is remobilised, and new close-to-optimum genotypes are generated and quickly increase in frequency, leading to more homogenous populations. Our results bring new insights into the role of standing genetic variation for adaptation in selfing populations
Conditions for maintaining and eroding pseudo-overdominance and its contribution to inbreeding depression
Get PDFClassical models that ignore linkage predict that deleterious recessive mutations should purge or fix within inbred populations, yet inbred populations often retain moderate to high segregating load. True overdominance could generate balancing selection strong enough to sustain inbreeding depression even within inbred populations, but this is considered rare. However, arrays of deleterious recessives linked in repulsion could generate appreciable pseudo-overdominance that would also sustain segregating load. We used simulations to explore how long pseudo-overdominant (POD) zones persist once created (e.g., by hybridization between populations fixed for alternative mildly deleterious mutations). Balanced haplotype loads, tight linkage, and moderate to strong cumulative selective effects all serve to maintain POD zones. Tight linkage is key, suggesting that such regions are most likely to arise and persist in low recombination regions (like inversions). Selection and drift unbalance the load, eventually eliminating POD zones, but this process is quite slow under strong pseudo-overdominance. Background selection accelerates the loss of weak POD zones but reinforces strong ones in inbred populations by disfavoring homozygotes. Models and empirical studies of POD dynamics within populations help us understand how POD zones may allow the load to persist, greatly affecting load dynamics and mating systems evolutio
Conditions for maintaining and eroding pseudo-overdominance and its contribution to inbreeding depression
Get PDFData from: The double edged sword: the demographic consequences of the evolution of self-fertilisation
No full textPhylogenies indicate that the transition from outcrossing to selfing is frequent, with selfing populations being more prone to extinction. The rates of transition to selfing and extinction, acting on different timescales, could explain the observed distributions of extant selfing species among taxa. However, phylogenetic and theoretical studies consider these mechanisms independently, i.e. transitions do not cause extinction. Here, we theoretically explore the demographic consequences of the evolution of self-fertilization. Deleterious mutations and mutations modifying the selfing rate are recurrently introduced and the number of offspring depends on individual fitness, allowing for a demographic feedback. We show that mutational meltdowns can be triggered in populations evolving near strict selfing. Populations having survived the demographic crash are more stable than ancestral outcrossing populations once deleterious mutations are purged. The relatively rapid time-scales in which extinctions occur indicate that during evolutionary transitions the accumulation of deleterious mutations may not be the cause of extinctions observed on longer time scales, which in turn could lead to the underestimation of transition rates from outcrossing to selfing
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Data from: Hidden genetic variance contributes to increase the short-term adaptive potential of selfing populations
No full textStanding genetic variation is considered a major contributor to the adaptive potential of species. The low heritable genetic variation observed in self-fertilising populations has led to the hypothesis that species with this mating system would be less likely to adapt. However, a non-negligible amount of cryptic genetic variation for polygenic traits, accumulated through negative linkage disequilibrium, could prove to be an important source of standing variation in self-fertilising species. To test this hypothesis we simulated populations under stabilizing selection subjected to an environmental change. We demonstrate that, when the mutation rate is high (but realistic), selfing populations are better able to store genetic variance than outcrossing populations through genetic associations, notably due to the reduced effective recombination rate associated with predominant selfing. Following an environmental shift, this diversity can be partially remobilized, which increases the additive variance and adaptive potential of predominantly (but not completely) selfing populations. In such conditions, despite initially lower observed genetic variance, selfing populations adapt as readily as outcrossing ones within a few generations. For low mutation rates, purifying selection impedes the storage of diversity through genetic associations, in which case, as previously predicted, the lower genetic variance of selfing populations results in lower adaptability compared to their outcrossing counterparts. The population size and the mutation rate are the main parameters to consider, as they are the best predictors of the amount of stored diversity in selfing populations. Our results and their impact on our knowledge of adaptation under high selfing rates are discussed
Hide and seek: hidden genetic variance contributing to the adaptive potential of selfing populations
No full textPreprint Ce rapport est disponible dans : BioRxivStanding genetic variation is considered a major contributor to the adaptive potential of species. The low heritable genetic variation observed in self-fertilising populations has led to the hypothesis that species with this particular mating system would be less likely to adapt. However, a non-negligible amount of cryptic genetic variation for polygenic traits, accumulated through negative linkage disequilibrium, could prove to be an important source of standing variation in self-fertilising species. Using a classical quantitative genetics model, we demonstrate that selfing populations are better able to store cryptic genetic variance than outcrossing populations, notably due to their lower recombination rate. Following a shift in the environment, this hidden diversity can be partially released, increasing the additive variance and adaptive potential of selfing populations. In such conditions, even though the process of adaptation itself is mating system dependant, selfers reach levels of fitness that are equal to or higher than outcrossing populations within a few generations. Outcrossing populations respond better to selection for the new optimum, but they maintain more genetic diversity resulting in a higher genetic load. In selfing populations, genetic diversity is remobilised, and new close-to-optimum genotypes are generated and quickly increase in frequency, leading to more homogenous populations. Our results bring new insights into the role of standing genetic variation for adaptation in selfing populations
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