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Emmanuelle Porcher - One of the best experts on this subject based on the ideXlab platform.
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Inbreeding depression under mixed outcrossing, Self-Fertilization and sib-mating
BMC evolutionary biology, 2016Co-Authors: Emmanuelle Porcher, Russell LandeAbstract:Biparental inbreeding, mating between two relatives, occurs at a low frequency in many natural plant populations, which also often have substantial rates of Self-Fertilization. Although biparental inbreeding is likely to influence the dynamics of inbreeding depression and the evolution of Selfing rates, it has received limited theoretical attention in comparison to Selfing. The only previous model suggested that biparental inbreeding can favour the maintenance of stable intermediate Selfing rates, but made unrealistic assumptions about the genetic basis of inbreeding depression. Here we extend a genetic model of inbreeding depression, describing nearly recessive lethal mutations at a very large number of loci, to incorporate sib-mating. We also include a constant component of inbreeding depression modelling the effects of mildly deleterious, nearly additive alleles. We analyze how observed rates of sib-mating influence the mean number of heterozygous lethals alleles and inbreeding depression in a population reproducing by a mixture of Self-Fertilization, sib-mating and outcrossing. We finally use the ensuing relationship between equilibrium inbreeding depression and population Selfing rate to infer the evolutionarily stable Selfing rates expected under such a mixed mating system. We show that for a given rate of inbreeding, sib-mating is more efficient at purging inbreeding depression than Selfing, because homozygosity of lethals increases more gradually through sib-mating than through Selfing. Because sib-mating promotes the purging of inbreeding depression and the evolution of Selfing, our genetic model of inbreeding depression also predicts that sib-mating is unlikely to maintain stable intermediate Selfing rates. Our results imply that even low rates of sib-mating affect plant mating system evolution, by facilitating the evolution of Selfing via more efficient purging of inbreeding depression. Alternative mechanisms, such as pollination ecology, are necessary to explain stable mixed Selfing and outcrossing.
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Inbreeding depression under mixed outcrossing, Self-Fertilization and sib-mating
BMC Evolutionary Biology, 2016Co-Authors: Emmanuelle Porcher, Russell LandeAbstract:Background: Biparental inbreeding, mating between two relatives, occurs at a low frequency in many natural plant populations, which also often have substantial rates of Self-Fertilization. Although biparental inbreeding is likely to influence the dynamics of inbreeding depression and the evolution of Selfing rates, it has received limited theoretical attention in comparison to Selfing. The only previous model suggested that biparental inbreeding can favour the maintenance of stable intermediate Selfing rates, but made unrealistic assumptions about the genetic basis of inbreeding depression. Here we extend a genetic model of inbreeding depression, describing nearly recessive lethal mutations at a very large number of loci, to incorporate sib-mating. We also include a constant component of inbreeding depression modelling the effects of mildly deleterious, nearly additive alleles. We analyze how observed rates of sib-mating influence the mean number of heterozygous lethals alleles and inbreeding depression in a population reproducing by a mixture of Self-Fertilization, sib-mating and outcrossing. We finally use the ensuing relationship between equilibrium inbreeding depression and population Selfing rate to infer the evolutionarily stable Selfing rates expected under such a mixed mating system. Results: We show that for a given rate of inbreeding, sib-mating is more efficient at purging inbreeding depression than Selfing, because homozygosity of lethals increases more gradually through sib-mating than through Selfing. Because sib-mating promotes the purging of inbreeding depression and the evolution of Selfing, our genetic model of inbreeding depression also predicts that sib-mating is unlikely to maintain stable intermediate Selfing rates. Conclusions: Our results imply that even low rates of sib-mating affect plant mating system evolution, by facilitating the evolution of Selfing via more efficient purging of inbreeding depression. Alternative mechanisms, such as pollination ecology, are necessary to explain stable mixed Selfing and outcrossing.
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maintenance of quantitative genetic variance under partial Self Fertilization with implications for evolution of Selfing
Genetics, 2015Co-Authors: Russell Lande, Emmanuelle PorcherAbstract:We analyze two models of the maintenance of quantitative genetic variance in a mixed-mating system of Self-Fertilization and outcrossing. In both models purely additive genetic variance is maintained by mutation and recombination under stabilizing selection on the phenotype of one or more quantitative characters. The Gaussian allele model (GAM) involves a finite number of unlinked loci in an infinitely large population, with a normal distribution of allelic effects at each locus within lineages Selfed for τ consecutive generations since their last outcross. The infinitesimal model for partial Selfing (IMS) involves an infinite number of loci in a large but finite population, with a normal distribution of breeding values in lineages of Selfing age τ . In both models a stable equilibrium genetic variance exists, the outcrossed equilibrium , nearly equal to that under random mating, for all Selfing rates, r , up to critical value, r ^ , the purging threshold , which approximately equals the mean fitness under random mating relative to that under complete Selfing. In the GAM a second stable equilibrium, the purged equilibrium , exists for any positive Selfing rate, with genetic variance less than or equal to that under pure Selfing; as r increases above r ^ the outcrossed equilibrium collapses sharply to the purged equilibrium genetic variance. In the IMS a single stable equilibrium genetic variance exists at each Selfing rate; as r increases above r ^ the equilibrium genetic variance drops sharply and then declines gradually to that maintained under complete Selfing. The implications for evolution of Selfing rates, and for adaptive evolution and persistence of predominantly Selfing species, provide a theoretical basis for the classical view of Stebbins that predominant Selfing constitutes an “evolutionary dead end.”
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Maintenance of Quantitative Genetic Variance Under Partial Self-Fertilization, with Implications for Evolution of Selfing
Genetics, 2015Co-Authors: Russell Lande, Emmanuelle PorcherAbstract:We analyze two models of the maintenance of quantitative genetic variance in a mixed-mating system of Self-Fertilization and outcrossing. In both models purely additive genetic variance is maintained by mutation and recombination under stabilizing selection on the phenotype of one or more quantitative characters. The Gaussian allele model (GAM) involves a finite number of unlinked loci in an infinitely large population, with a normal distribution of allelic effects at each locus within lineages Selfed for τ consecutive generations since their last outcross. The infinitesimal model for partial Selfing (IMS) involves an infinite number of loci in a large but finite population, with a normal distribution of breeding values in lineages of Selfing age τ. In both models a stable equilibrium genetic variance exists, the outcrossed equilibrium, nearly equal to that under random mating, for all Selfing rates, r, up to critical value, Embedded Image, the purging threshold, which approximately equals the mean fitness under random mating relative to that under complete Selfing. In the GAM a second stable equilibrium, the purged equilibrium, exists for any positive Selfing rate, with genetic variance less than or equal to that under pure Selfing; as r increases above Embedded Image the outcrossed equilibrium collapses sharply to the purged equilibrium genetic variance. In the IMS a single stable equilibrium genetic variance exists at each Selfing rate; as r increases above Embedded Image the equilibrium genetic variance drops sharply and then declines gradually to that maintained under complete Selfing. The implications for evolution of Selfing rates, and for adaptive evolution and persistence of predominantly Selfing species, provide a theoretical basis for the classical view of Stebbins that predominant Selfing constitutes an “evolutionary dead end.”
Russell Lande - One of the best experts on this subject based on the ideXlab platform.
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Inbreeding depression under mixed outcrossing, Self-Fertilization and sib-mating
BMC evolutionary biology, 2016Co-Authors: Emmanuelle Porcher, Russell LandeAbstract:Biparental inbreeding, mating between two relatives, occurs at a low frequency in many natural plant populations, which also often have substantial rates of Self-Fertilization. Although biparental inbreeding is likely to influence the dynamics of inbreeding depression and the evolution of Selfing rates, it has received limited theoretical attention in comparison to Selfing. The only previous model suggested that biparental inbreeding can favour the maintenance of stable intermediate Selfing rates, but made unrealistic assumptions about the genetic basis of inbreeding depression. Here we extend a genetic model of inbreeding depression, describing nearly recessive lethal mutations at a very large number of loci, to incorporate sib-mating. We also include a constant component of inbreeding depression modelling the effects of mildly deleterious, nearly additive alleles. We analyze how observed rates of sib-mating influence the mean number of heterozygous lethals alleles and inbreeding depression in a population reproducing by a mixture of Self-Fertilization, sib-mating and outcrossing. We finally use the ensuing relationship between equilibrium inbreeding depression and population Selfing rate to infer the evolutionarily stable Selfing rates expected under such a mixed mating system. We show that for a given rate of inbreeding, sib-mating is more efficient at purging inbreeding depression than Selfing, because homozygosity of lethals increases more gradually through sib-mating than through Selfing. Because sib-mating promotes the purging of inbreeding depression and the evolution of Selfing, our genetic model of inbreeding depression also predicts that sib-mating is unlikely to maintain stable intermediate Selfing rates. Our results imply that even low rates of sib-mating affect plant mating system evolution, by facilitating the evolution of Selfing via more efficient purging of inbreeding depression. Alternative mechanisms, such as pollination ecology, are necessary to explain stable mixed Selfing and outcrossing.
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Inbreeding depression under mixed outcrossing, Self-Fertilization and sib-mating
BMC Evolutionary Biology, 2016Co-Authors: Emmanuelle Porcher, Russell LandeAbstract:Background: Biparental inbreeding, mating between two relatives, occurs at a low frequency in many natural plant populations, which also often have substantial rates of Self-Fertilization. Although biparental inbreeding is likely to influence the dynamics of inbreeding depression and the evolution of Selfing rates, it has received limited theoretical attention in comparison to Selfing. The only previous model suggested that biparental inbreeding can favour the maintenance of stable intermediate Selfing rates, but made unrealistic assumptions about the genetic basis of inbreeding depression. Here we extend a genetic model of inbreeding depression, describing nearly recessive lethal mutations at a very large number of loci, to incorporate sib-mating. We also include a constant component of inbreeding depression modelling the effects of mildly deleterious, nearly additive alleles. We analyze how observed rates of sib-mating influence the mean number of heterozygous lethals alleles and inbreeding depression in a population reproducing by a mixture of Self-Fertilization, sib-mating and outcrossing. We finally use the ensuing relationship between equilibrium inbreeding depression and population Selfing rate to infer the evolutionarily stable Selfing rates expected under such a mixed mating system. Results: We show that for a given rate of inbreeding, sib-mating is more efficient at purging inbreeding depression than Selfing, because homozygosity of lethals increases more gradually through sib-mating than through Selfing. Because sib-mating promotes the purging of inbreeding depression and the evolution of Selfing, our genetic model of inbreeding depression also predicts that sib-mating is unlikely to maintain stable intermediate Selfing rates. Conclusions: Our results imply that even low rates of sib-mating affect plant mating system evolution, by facilitating the evolution of Selfing via more efficient purging of inbreeding depression. Alternative mechanisms, such as pollination ecology, are necessary to explain stable mixed Selfing and outcrossing.
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maintenance of quantitative genetic variance under partial Self Fertilization with implications for evolution of Selfing
Genetics, 2015Co-Authors: Russell Lande, Emmanuelle PorcherAbstract:We analyze two models of the maintenance of quantitative genetic variance in a mixed-mating system of Self-Fertilization and outcrossing. In both models purely additive genetic variance is maintained by mutation and recombination under stabilizing selection on the phenotype of one or more quantitative characters. The Gaussian allele model (GAM) involves a finite number of unlinked loci in an infinitely large population, with a normal distribution of allelic effects at each locus within lineages Selfed for τ consecutive generations since their last outcross. The infinitesimal model for partial Selfing (IMS) involves an infinite number of loci in a large but finite population, with a normal distribution of breeding values in lineages of Selfing age τ . In both models a stable equilibrium genetic variance exists, the outcrossed equilibrium , nearly equal to that under random mating, for all Selfing rates, r , up to critical value, r ^ , the purging threshold , which approximately equals the mean fitness under random mating relative to that under complete Selfing. In the GAM a second stable equilibrium, the purged equilibrium , exists for any positive Selfing rate, with genetic variance less than or equal to that under pure Selfing; as r increases above r ^ the outcrossed equilibrium collapses sharply to the purged equilibrium genetic variance. In the IMS a single stable equilibrium genetic variance exists at each Selfing rate; as r increases above r ^ the equilibrium genetic variance drops sharply and then declines gradually to that maintained under complete Selfing. The implications for evolution of Selfing rates, and for adaptive evolution and persistence of predominantly Selfing species, provide a theoretical basis for the classical view of Stebbins that predominant Selfing constitutes an “evolutionary dead end.”
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Maintenance of Quantitative Genetic Variance Under Partial Self-Fertilization, with Implications for Evolution of Selfing
Genetics, 2015Co-Authors: Russell Lande, Emmanuelle PorcherAbstract:We analyze two models of the maintenance of quantitative genetic variance in a mixed-mating system of Self-Fertilization and outcrossing. In both models purely additive genetic variance is maintained by mutation and recombination under stabilizing selection on the phenotype of one or more quantitative characters. The Gaussian allele model (GAM) involves a finite number of unlinked loci in an infinitely large population, with a normal distribution of allelic effects at each locus within lineages Selfed for τ consecutive generations since their last outcross. The infinitesimal model for partial Selfing (IMS) involves an infinite number of loci in a large but finite population, with a normal distribution of breeding values in lineages of Selfing age τ. In both models a stable equilibrium genetic variance exists, the outcrossed equilibrium, nearly equal to that under random mating, for all Selfing rates, r, up to critical value, Embedded Image, the purging threshold, which approximately equals the mean fitness under random mating relative to that under complete Selfing. In the GAM a second stable equilibrium, the purged equilibrium, exists for any positive Selfing rate, with genetic variance less than or equal to that under pure Selfing; as r increases above Embedded Image the outcrossed equilibrium collapses sharply to the purged equilibrium genetic variance. In the IMS a single stable equilibrium genetic variance exists at each Selfing rate; as r increases above Embedded Image the equilibrium genetic variance drops sharply and then declines gradually to that maintained under complete Selfing. The implications for evolution of Selfing rates, and for adaptive evolution and persistence of predominantly Selfing species, provide a theoretical basis for the classical view of Stebbins that predominant Selfing constitutes an “evolutionary dead end.”
Philippe Jarne - One of the best experts on this subject based on the ideXlab platform.
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Experimental Evidence for the Negative Effects of Self-Fertilization on the Adaptive Potential of Populations
Current Biology - CB, 2017Co-Authors: Elsa Noël, Philippe Jarne, Sylvain Glémin, Alicia Mackenzie, Adeline Segard, Violette Sarda, Patrice DavidAbstract:Self-Fertilization is widely believed to be an ''evolu-tionary dead end'' [1, 2], increasing the risk of extinction [3] and the accumulation of deleterious mutations in genomes [4]. Strikingly, while the failure to adapt has always been central to the dead-end hypothesis [1, 2], there are no quantitative genetic selection experiments comparing the response to positive selection in Selfing versus outcrossing populations. Here we studied the response to selection on a morphological trait in laboratory populations of a hermaphroditic, Self-fertile snail under either Selfing or outcrossing. We applied both treatments to two types of populations: some having undergone frequent Selfing and purged a substantial fraction of their mutation load in their recent history [5], and others continuously maintained under outcrossing. Populations with a history of outcrossing respond faster to selection than those that have experienced Selfing. In addition, when Self-Fertilization occurs during selection, the response is initially fast but then rapidly slows, while out-crossing populations maintain their response throughout the experiment. This occurs irrespective of past Selfing history, suggesting that high levels of inbreeding depression, contrary to expectation [6], do not set strong limits to the response to selection under inbreeding, at least at the timescale of a few generations. More surprisingly, pheno-typic variance is consistently higher under Selfing, although it quickly becomes less responsive to selection. This implies an increase in non-heritable variance, hence a breakdown of developmental canalization [7] under Selfing. Our findings provide the first empirical support of the short-term positive and long-term negative effects of Selfing on adaptive potential.
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reduced mate availability leads to evolution of Self Fertilization and purging of inbreeding depression in a hermaphrodite
Evolution, 2016Co-Authors: Elsa Noël, Philippe Jarne, Violette Sarda, Yohann Chemtob, Tim Janicke, Benjamin Pelissie, Patrice DavidAbstract:: Basic models of mating-system evolution predict that hermaphroditic organisms should mostly either cross-fertilize, or Self-fertilize, due to Self-reinforcing coevolution of inbreeding depression and outcrossing rates. However transitions between mating systems occur. A plausible scenario for such transitions assumes that a decrease in pollinator or mate availability temporarily constrains outcrossing populations to Self-fertilize as a reproductive assurance strategy. This should trigger a purge of inbreeding depression, which in turn encourages individuals to Self-fertilize more often and finally to reduce male allocation. We tested the predictions of this scenario using the freshwater snail Physa acuta, a Self-compatible hermaphrodite that preferentially outcrosses and exhibits high inbreeding depression in natural populations. From an outbred population, we built two types of experimental evolution lines, controls (outcrossing every generation) and constrained lines (in which mates were often unavailable, forcing individuals to Self-fertilize). After ca. 20 generations, individuals from constrained lines initiated Self-Fertilization earlier in life and had purged most of their inbreeding depression compared to controls. However, their male allocation remained unchanged. Our study suggests that the mating system can rapidly evolve as a response to reduced mating opportunities, supporting the reproductive assurance scenario of transitions from outcrossing to Selfing.
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a problem with the estimate of Self Fertilization depression in the hermaphrodite freshwater snail bulinus truncatus the effect of grouping
Evolution, 1994Co-Authors: Claudie Doums, Bernard Delay, Philippe JarneAbstract:The evolution of Self-Fertilization has been the subject of both numerous theoretical and empirical studies (reviewed by Jain 1976; Charlesworth and Charlesworth 1987; Uyenoyama et al. 1993; Jarne and Charlesworth 1993). These studies have shown that inbreeding depression, that is, the lowered fitness of inbred as compared with outbred individuals, is an important factor determining this evolution. Although most research has focused on plants, some studies have been performed on hermaphrodite animals (see Jarne and Charlesworth 1993) and particularly freshwater snails (see Jarne et al. 1993). Differences in survival rates between progeny of Selfing and outcrossing individuals have been shown and interpreted as resulting from inbreeding depression. Selfing snails also have a lower fecundity than outcrossing snails. The whole effect (fecundity of parents and inbreeding depression of their progeny) has been referred to as Self-Fertilization depression (Jarne et al. 1991). However, specific problems may arise when estimating Self-Fertilization depression in animals. In experiments on hermaphroditic freshwater snails, Selfed progenies have been produced usually by isolated virgin adults, and outcrossed progenies have been produced by grouped adults (review in Jarne et al. 1993). The effect of the mating system (outcrossing) and the effect of grouping are therefore associated when analyzing the results of outcrossing. It has been shown for various species of freshwater snails that both population density and size influence growth, survival, and fecundity (Chernin and Michelson 1956a,b; Thomas et al. 1974; Thomas and Benjamin 1974; Ahmed et al. 1986; Chaudhry and Morgan 1987). Increased density and population size is generally associated with a reduced fecundity and could lead to an underestimate of Self-Fertilization depression. In this paper, we investigate whether previous estimates of Self-Fertilization depression may have been biased by a grouping effect. By using aphallic individuals of the hermaphrodite freshwater snail Bulinus truncatus (see below), we can estimate the effect of grouping Selffertilized for isolated and grouped snails. This is done by comparing the fitness of isolated snails with that of individuals at various group size and densities. Bulinus truncatus is a Self-fertile hermaphrodite with two sexual morphs, euphallic and aphallic individuals, occurring in natural populations. Euphallic snails can Self-fertilize as well as outcross as males or as females. Aphallic snails are characterized by the absence of the male copulatory organ (Larambergue 1939). They can Selffertilize and receive sperm from an euphallic partner. However, they cannot transfer their own sperm to a partner (Larambergue 1939). No mutual exchange of sperm occurs during copulation in hermaphrodite freshwater snails: one individual acts as the female when its partner acts as the male. The determinism of aphally is still unclear; some results indicate a genetic determinism (Larambergue 1939), whereas others point strongly to the role of temperature (Schrag and Read 1992). A consequence of aphally is that purely aphallic populations can only Self-fertilize. By using aphallic snails, the consequences of grouping can therefore be estimated without interference of the mating system. The aim of the present work is to test (1) whether a grouping effect occurs in the conditions previously used to analyze the Self-Fertilization depression (about 150 mL of water per snail with group size of 5 to 10 snails) (Jarne and Delay 1990; Jarne et al.
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do Self Fertilization and genetic drift promote a very low genetic variability in the allotetraploid bulinus truncatus gastropoda planorbidae populations
Genetics Research, 1993Co-Authors: Flobert Njiokou, Bernard Delay, Christian Bellec, Patrick Berrebi, Philippe JarneAbstract:Bulinus truncatus , one of the intermediate hosts of the genus Schistosoma is an hermaphrodite freshwater snail species occupying a variety of environments over almost all Africa. These environments are subjected to large variations in water availability. B. truncatus is allotetraploid and its populations exhibit various frequencies of aphallic individuals (unable to reproduce as male). Both traits probably favour a reproduction by Self-Fertilization. Here we investigate the genetic structure of populations of B. truncatus of Niger and Ivory Coast using protein electrophoresis to analyse the influence of the environment and of both the last traits. To obtain an estimate of the true heterozygosity in this allotetraploid species, we analyse independently the two diploid loci at each tetraploid locus. Our study indicates (i) an extremely low intrapopulation polymorphism with most alleles fixed and the total absence of heterozygotes and (ii) low differentiation between populations. These results indicate high gene flow between populations. However, the existence of private alleles sometimes at high frequency, the low polymorphism and the lack of heterozygotes point to the role of both genetic drift and Self-Fertilization, the second amplifying the genetic consequences of the first.
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Self-Fertilization VERSUS CROSS-Fertilization IN THE HERMAPHRODITIC FRESHWATER SNAIL BULINUS GLOBOSUS.
Evolution, 1991Co-Authors: Philippe Jarne, Luc Finot, Bernard Delay, Louis ThalerAbstract:Self-Fertilization depression of fitness in the freshwater hermaphroditic snail Bulinus globosus, an intermediate host of the parasitic trematode Schistosoma, has been studied in a strain originating from Niger. B. globosus is an outcrosser that can Self-fertilize when isolated before any copulation has occurred. The Self-Fertilization depression has been estimated during two successive generations. In the first generation, Selfing was compared to outcrossing. Within each mating system group, Selfing and outcrossing were compared again in the second generation. A striking difference was shown in favor of cross-Fertilization for the number of eggs laid, the survival at birth of young snails and the number of snails reaching sexual maturity. The overall Self-Fertilization depression is 0.920 after two generations of Selfing. We discuss the relative role of Selfing and outcrossing in the evolution of freshwater snail populations.
Pierreolivier Cheptou - One of the best experts on this subject based on the ideXlab platform.
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does the evolution of Self Fertilization rescue populations or increase the risk of extinction
Annals of Botany, 2019Co-Authors: Pierreolivier CheptouAbstract:Background and aims As a major evolutionary transition in seed plants, the evolution of plant mating systems has been much debated in evolutionary ecology. Over the last 10 years, well-established patterns of evolution have emerged. On the one hand, experimental studies have shown that Self-Fertilization is likely to evolve in a few generations (microevolution) as a response to rapid environmental change (e.g. pollinator decline), eventually rescuing a population. On the other, phylogenetic studies have demonstrated that repeated evolution towards Self-Fertilization (macroevolution) leads to a higher risk of lineage extinction and is thus likely to be disadvantageous in the long term. Scope In either case - the short-term or long-term evolution of Self-Fertilization (Selfing) - these findings indicate that a mating system is not neutral with respect to population or lineage persistence. They also suggest that Selfing can have contrasting effects depending on time scale. This raises the question of whether mating system evolution can rescue populations facing environmental change. In this review, empirical and theoretical evidence of the direct and indirect effects of mating systems on population demography and lineage persistence were analysed. A simple theoretical evolutionary rescue model was also developed to investigate the potential for evolutionary rescue through Selfing. Key findings Demographic studies consistently show a short-term advantage of Selfing provided by reproductive assurance, but a long-term disadvantage for Selfing lineages, suggesting indirect genomic consequences of Selfing (e.g. mutation load and lower adaptability). However, our theoretical evolutionary rescue model found that even in the short term, while mating system evolution can lead to evolutionary rescue, it can also lead to evolutionary suicide, due to the inherent frequency-dependent selection of mating system traits. Conclusions These findings point to the importance of analysing the demographic consequences of Self-Fertilization in order to predict the effect of Selfing on population persistence as well as take into account the indirect genomic consequences of Selfing. The pace at which processes such as inbreeding depression, purging, reproductive assurance and genomic rearrangements occur after the Selfing transition is the key to clarifying whether or not Selfing will result in evolutionary rescue.
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allee effect and Self Fertilization in hermaphrodites reproductive assurance in a structured metapopulation
Evolution, 2008Co-Authors: Antoine Dornier, Francois Munoz, Pierreolivier CheptouAbstract:Reproductive assurance through Selfing during colonization events or when population densities are low has often been put forward as a mechanism selecting for the evolution of Self-Fertilization. Such arguments emphasize on the role of both local demography and metapopulation processes. We developed a model for the evolution of Self-Fertilization in a structured metapopulation in which local densities are not steady because of population growth. Reproduction by Selfing is density-independent (reproductive assurance) but Selfed seeds endure inbreeding depression, whereas reproduction by outcrossing is density-dependent (Allee effect). First, we derived an analytical criterion for metapopulation viability as a function of the Selfing rate and metapopulation parameters. We show that outcrossers can develop a viable metapopulation when they produce a high amount of dispersal seeds that counterbalances their incapacity to found new populations from low densities. Second, the model shows there is a positive feedback between demography and outcrossing rates, leading to either complete outcrossing or Selfing. Specifically, we illustrate that inbreeding depression can paradoxically favor the evolution of Selfing because of its negative effect on density. Also, complete outcrossing can be selected despite pollen limitation, although it does not provide a full seed set. This model underlines the influence of the mating system both on demography and gene dynamics in a metapopulation context.
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allee effect and Self Fertilization in hermaphrodites reproductive assurance in demographically stable populations
Evolution, 2004Co-Authors: Pierreolivier CheptouAbstract:The fact that Selfing increases seed set (reproductive assurance) has often been put forward as an important selective force for the evolution of Selfing. However, the role of reproductive assurance in hermaphroditic populations is far from being clear because of a lack of theoretical work. Here, I propose a theoretical model that analyzes Self-Fertilization in the presence of reproductive assurance. Because reproductive assurance directly influences the per capita growth rate, I developed an explicit demographic model for partial Selfers in the presence of reproductive assurance, specifically when outcrossing is limited by the possibility of pollen transfer (Allee effect). Mating system parameters are derived as a function of the underlying demographical parameters. The functional link between population demography and mating system parameters (reproductive assurance, Selfing rate) can be characterized. The demographic model permits the analysis of the evolution of Self-Fertilization in stable populations when reproductive assurance occurs. The model reveals some counterintuitive results such as the fact that increasing the fraction of Selfed ovules can, in certain circumstances, increase the fraction of outcrossed ovules. Moreover, I demonstrate that reproductive assurance per se cannot account for the evolution of stable mixed Selfing rates. Also, the model reveals that the extinction of outcrossing populations depends on small changes in population density (ecological perturbations), while the transition from outcrossing to Selfing can, in certain cases, lead the population to extinction (evolutionary suicide). More generally, this paper highlights the fact that Self-Fertilization affects both the dynamics of individuals and the dynamics of Selfing genes in hermaphroditic populations.
Mark O. Johnston - One of the best experts on this subject based on the ideXlab platform.
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Flower Development and the Evolution of Self-Fertilization in Amsinckia: The Role of Heterochrony
Evolutionary Biology, 2010Co-Authors: Ping Li, Mark O. JohnstonAbstract:We studied the development of 26 flower traits under natural conditions in three clades of the genus Amsinckia (Boraginaceae). Each clade contained both a derived highly Self-fertilizing taxon and an ancestral more highly outcrossing taxon. The more outcrossing taxa contained two flower morphs—pins and thrums—with opposite positioning of the sex organs (heterostyly). The highly Selfing taxa had smaller flowers with sex organs in close proximity (homostyly). Growth trajectories were quantified over the entire or nearly the entire period from primordium initiation to flower opening. These trajectories were compared in the heterochronic framework and, in contrast with previous studies, character size was tracked over time rather than relative to another character. We focused on three hypotheses: (1) The distinct developmental trajectories leading to pins and thrums should be similar in all clades, while the trajectories leading to homostylous flowers might differ among clades. This was supported. Specifically, contrasting growth rates of stamen and pistil heights in heterostylous flowers caused pin and thrum flowers to have the reciprocal arrangement of anther and stigma heights. From the viewpoint of heterochrony, the decreased size (paedomorphosis) of the homostylous morph, compared to pins and thrums, resulted from decreased growth rate (neoteny) and earlier offset (progenesis) in all clades. Nevertheless, multiple heterochronic processes were involved in the mosaic development and evolution of homostylous flowers. (2) We tested the hypothesis that small, Self-fertilizing flowers have reduced development times, one of the proposed selective advantages of increased Self-Fertilization rates. We found in contrast that developmental duration of homostylous flowers was either the same (two clades) or longer (one clade) compared to duration of pins and thrums. (3) Finally, we tested von Baer’s Law, which proposes that developmental differences among closely related taxa should arise later in development than differences among more distantly related taxa. Von Baer’s Law was supported strongly among homostyles, moderately among thrums and weakly among pins.
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quantitative genetic variation in populations of amsinckia spectabilis that differ in rate of Self Fertilization
Evolution, 2009Co-Authors: Magdalena P Bartkowska, Mark O. JohnstonAbstract:Self-Fertilization is expected to reduce genetic diversity within populations and consequently to limit adaptability to changing environments. Little is known, however, about the way the evolution of Self-Fertilization changes the amount or pattern of the components of genetic variation in natural populations. In this study, a reciprocal North Carolina II design and maximum-likelihood methods were implemented to investigate the genetic basis of variation for 15 floral and vegetative traits in four populations of the annual plant Amsinckia spectabilis (Boraginaceae) differing in mating system. Six variance components were estimated according to Cockerham and Weir's "bio" model c. Compared to the three partially Selfing populations, we found significantly lower levels of nuclear variance for several traits in the nearly completely Self-fertilizing population. Furthermore, for 11 of 15 traits we did not detect nuclear variation to be significantly greater than zero. We also found high maternal variance in one of the partially Selfing populations for several traits, and little dominance variance in any population. These results are in agreement with the evolutionary dead-end hypothesis for highly Self-fertilizing taxa.
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correlated evolution of Self Fertilization and inbreeding depression an experimental study of nine populations of amsinckia boraginaceae
Evolution, 1996Co-Authors: Mark O. Johnston, Daniel J. SchoenAbstract:The relation between inbreeding depression and rate of Self-Fertilization was studied in nine natural pop- ulations of the annual genus Amsinckia. The study included two clades (phylogenetic lineages) in which small-flowered, homostylous populations or species are believed to have evolved from large-flowered, heterostylous, Self-compatible ones. In one lineage the small-flowered species is tetraploid with disomic inheritance. Rates of Self-Fertilization were 25% to 55% in the four large-flowered, heterostylous populations; 72% in a large-flowered but homostylous population; and greater than 99.5% in the four small-flowered, homostylous populations, which produce seed autonomously. When present, inbreeding depression occurred in the fertility but not the survival components of fitness. Using a cumulative fitness measure incorporating both survival and fertility (flower number), we found inbreeding depression to be lower in the four very highly Self-fertilizing populations than in the five intermediate ones. The Spearman rank correlation between inbreeding depression and Selfing rate for the nine populations was -0.50, but was not statistically significant (P = 0.12). Inbreeding depression was greater in the two tetraploid populations than in the very highly Self-fertilizing, diploid ones. Phenotypic stability of progeny from Self-Fertilization tended to be higher in populations with lower inbreeding depression. We conclude that levels of Self-Fertilization and inbreeding depression in Amsinckia are de- termined more by other factors than by each other. Estimates of mutation rates and dominance coefficients of deleterious alleles, obtained from a companion study of the four highly Self-fertilizing populations, suggest that a strong relationship may not be expected. We discuss the relationship of the present results to current theory of the coevolution of Self- Fertilization and inbreeding depression.
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effects of cross and Self Fertilization on progeny fitness in lobelia cardinalis and l siphilitica
Evolution, 1992Co-Authors: Mark O. JohnstonAbstract:Inbreeding depression, or the decreased fitness of progeny derived from Self-Fertilization as compared to outcrossing, is thought to be the most general factor affecting the evolution of Self-Fertilization in plants. Nevertheless, data on inbreeding depression in fitness characters are almost nonexistent for perennials observed in their natural environments. In this study I measured inbreeding depression in both survival and fertility in two sympatric, short-lived, perennial herbs: hummingbird-pollinated Lobelia cardinalis (two populations) and bumblebee-pollinated L. siphilitica (one population). Crosses were performed by hand in the field, and seedlings germinated in the greenhouse. Levels of inbreeding depression were determined for one year in the greenhouse and for two to three years for seedlings transplanted back to the natural environment. Fertility was measured as flower number, which is highly correlated with seed production under natural conditions in these populations. Inbreeding depression was assessed in three ways: 1) survival and fertility within the different age intervals; 2) cumulative survival from the seed stage through each age interval; and 3) net fertility, or the expected fertility of a seed at different ages. Net fertility is a comprehensive measure of fitness combining survival and flower number. In all three populations, Selfing had nonsignificant effects on the number and size of seeds. Lobelia siphilitica and one population of L. cardinalis exhibited significant levels of inbreeding depression between seed maturation and germination, excluding the consideration of possible differences in dormancy or longterm viability in the soil. There was no inbreeding depression in subsequent survival in the greenhouse in any population. In the field, significant survival differences between Selfed and outcrossed progeny occurred only in two years and in only one population of L. cardinalis. For both survival and fertility there was little evidence for the expected differences among families in inbreeding depression. Compared to survival, inbreeding depression in fertility (flower number) tended to be much higher. By first-year flower production, the combined effects on survival and flower number caused inbreeding depression in net fertility to reach 54%, 34% and 71% for L. siphilitica and the two populations of L. cardinalis. By the end of the second year of flowering in the field, inbreeding depression in net fertility was 53% for L. siphilitica and 54% for one population of L. cardinalis. For the other population of L. cardinalis, these values were 76% through the second year of flowering and 83% through the third year. Such high levels of inbreeding depression should strongly influence selection on those characters affecting Self-Fertilization rates in these two species.