Epistasis, inbreeding depression and the evolution of self-fertilization

Selection, Load and Inbreeding Depression in a Large Metapopulation

Genetics ◽

10.1093/genetics/160.3.1191 ◽

2002 ◽

Vol 160 (3) ◽

pp. 1191-1202 ◽

Cited By ~ 1

Author(s):

Michael C Whitlock

Keyword(s):

Population Structure ◽

Inbreeding Depression ◽

Population Subdivision ◽

Response To Selection ◽

Mutation Load ◽

Deleterious Alleles ◽

Subdivided Population ◽

Soft Selection ◽

Mean Fitness ◽

The Mean

Abstract The subdivision of a species into local populations causes its response to selection to change, even if selection is uniform across space. Population structure increases the frequency of homozygotes and therefore makes selection on homozygous effects more effective. However, population subdivision can increase the probability of competition among relatives, which may reduce the efficacy of selection. As a result, the response to selection can be either increased or decreased in a subdivided population relative to an undivided one, depending on the dominance coefficient FST and whether selection is hard or soft. Realistic levels of population structure tend to reduce the mean frequency of deleterious alleles. The mutation load tends to be decreased in a subdivided population for recessive alleles, as does the expected inbreeding depression. The magnitude of the effects of population subdivision tends to be greatest in species with hard selection rather than soft selection. Population structure can play an important role in determining the mean fitness of populations at equilibrium between mutation and selection.

The role of self-incompatibility systems in the prevention of bi-parental inbreeding

10.7287/peerj.preprints.3042v1 ◽

2017 ◽

Author(s):

Tara N Furstenau ◽

Reed A Cartwright

Keyword(s):

Inbreeding Depression ◽

Pollen Dispersal ◽

Dispersal Distance ◽

Inbreeding Avoidance ◽

Self Incompatibility ◽

Plant Populations ◽

Population Sizes ◽

Self Fertilization ◽

Individual Based Simulation

Hermaphroditic plants experience inbreeding through both self-fertilization and bi-parental inbreeding. Therefore, many plant species have evolved either heteromorphic (morphology-based) or homomorphic (molecular-based) self-incompatibility (SI) systems. These SI systems limit extreme inbreeding through self-fertilization and, in the case of homomorphic SI systems, have the potential to limit bi-parental inbreeding, which is common when dispersal is restricted to a local region. Homomorphic SI species are prevalent across the angiosperms, and it is often assumed that the potential to reduce bi-parental inbreeding may be a factor in their success. To test this assumption, we developed a spatially-explicit, individual-based simulation of plant populations with either heteromorphic SI or one of three different types of homomorphic SI. In our simulations, we varied dispersal distance and the presence of inbreeding depression. We found that autozygosity in the homomorphic SI populations was significantly lower than in the heteromorphic SI populations and that this reduction was due to bi-parental inbreeding avoidance. As expected, the differences between the homomorphic and heteromorphic SI populations were more pronounced when seed and pollen dispersal was limited. However, levels of homozygosity and inbreeding depression between these plant populations were not different. At low dispersal, homomorphic SI populations also suffered reduced female fecundity and had smaller census population sizes. Our results suggest that bi-parental inbreeding avoidance was unlikely to be a major driver in the evolution of homomorphic SI systems.

The role of self-incompatibility systems in the prevention of bi-parental inbreeding

10.7287/peerj.preprints.3042 ◽

2017 ◽

Author(s):

Tara N Furstenau ◽

Reed A Cartwright

Keyword(s):

Inbreeding Depression ◽

Pollen Dispersal ◽

Dispersal Distance ◽

Inbreeding Avoidance ◽

Self Incompatibility ◽

Plant Populations ◽

Population Sizes ◽

Self Fertilization ◽

Individual Based Simulation

Hermaphroditic plants experience inbreeding through both self-fertilization and bi-parental inbreeding. Therefore, many plant species have evolved either heteromorphic (morphology-based) or homomorphic (molecular-based) self-incompatibility (SI) systems. These SI systems limit extreme inbreeding through self-fertilization and, in the case of homomorphic SI systems, have the potential to limit bi-parental inbreeding, which is common when dispersal is restricted to a local region. Homomorphic SI species are prevalent across the angiosperms, and it is often assumed that the potential to reduce bi-parental inbreeding may be a factor in their success. To test this assumption, we developed a spatially-explicit, individual-based simulation of plant populations with either heteromorphic SI or one of three different types of homomorphic SI. In our simulations, we varied dispersal distance and the presence of inbreeding depression. We found that autozygosity in the homomorphic SI populations was significantly lower than in the heteromorphic SI populations and that this reduction was due to bi-parental inbreeding avoidance. As expected, the differences between the homomorphic and heteromorphic SI populations were more pronounced when seed and pollen dispersal was limited. However, levels of homozygosity and inbreeding depression between these plant populations were not different. At low dispersal, homomorphic SI populations also suffered reduced female fecundity and had smaller census population sizes. Our results suggest that bi-parental inbreeding avoidance was unlikely to be a major driver in the evolution of homomorphic SI systems.

The Genomics of Selfing in Maize (Zea mays ssp. mays): Catching Purging in the Act

10.1101/594812 ◽

2019 ◽

Cited By ~ 2

Author(s):

Kyria Roessler ◽

Aline Muyle ◽

Concepcion M. Diez ◽

Garren R.J. Gaut ◽

Alexandros Bousios ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Zea Mays ◽

Inbreeding Depression ◽

Recombination Rate ◽

Principal Component ◽

Genetic Tool ◽

Deleterious Alleles ◽

Self Fertilization ◽

Genomic Scale ◽

Short Timeframe

ABSTRACTIn plants, self-fertilization is both an important reproductive strategy and a valuable genetic tool. In theory, selfing increases homozygosity at a rate of 0.50 per generation. Increased homozygosity can uncover recessive deleterious variants and lead to inbreeding depression, unless it is countered by the loss of these variants by genetic purging. Here we investigated the dynamics of purging on genomic scale by testing three predictions. The first was that heterozygous, putatively deleterious SNPs were preferentially lost from the genome during continued selfing. The second was that the loss of deleterious SNPs varied as a function of recombination rate, because recombination increases the efficacy of selection by uncoupling linked variants. Finally, we predicted that genome size (GS) decreases during selfing, due to the purging of deleterious transposable element (TE) insertions. We tested these three predictions by following GS and SNP variants in a series of selfed maize (Zea mays ssp. mays) lines over six generations. In these lines, putatively deleterious alleles were purged, and purging was more pronounced in highly recombining regions. Homozygosity increased more slowly than expected; instead of increasing by 50% each generation, it increased by 35% to 40%. Finally, three lines showed dramatic decreases in GS, losing an average of 398 Mb from their genomes over the short timeframe of our experiment. TEs were the principal component of loss, and GS loss was more likely for lineages that began with more TE and more chromosomal knob repeats. Overall, this study documented remarkable GS loss – as much DNA as three Arabidopsis thaliana genomes, on average - in only a few generations of selfing.

Heterosis from local drift load is likely insufficient to favor reversions to outcrossing

10.1101/273946 ◽

2018 ◽

Author(s):

Alexander Harkness ◽

Emma E. Goldberg ◽

Yaniv J Brandvain

Keyword(s):

Inbreeding Depression ◽

Population Genetic ◽

Allelic Variation ◽

Initial Increase ◽

Short Term ◽

Genetic Theory ◽

Evolutionary Trajectory ◽

Deleterious Alleles ◽

Self Fertilization ◽

Cross Fertilization

AbstractThe evolutionary trajectory from cross-to self-fertilization is widely documented in nature, but results from several taxa also suggest that outcrossing may evolve in a formerly selfing population. Population genetic theory explains that selfing can evolve when its advantages overcome its immediate cost of inbreeding depression, but that this process will not run in reverse because a self-fertilizing population purges itself of inbreeding depression. That is, the primary short-term advantage of cross-fertilization over self-fertilization depends on the existence of deleterious alleles exposed upon inbreeding. Here, we explore whether outcrossing can evolve in selfing populations if allelic variation exists as divergence among populations. We consider two monomorphic populations of entirely self-fertilizing individuals, introduce a modifier allele that increases the rate of cross-fertilization, and investigate whether the heterosis among populations is sufficient for the modifier to invade and fix. We find that, despite an initial increase in the frequency of the outcrossing modifier, its fixation is possible only when populations harbor extremely large unique fixed genetic loads. These rare reversions to outcrossing become more likely as the load becomes more polygenic, or when the modifier appears on a rare background, such as by dispersal of an outcrossing genotype into a selfing population.

Effects of partial selfing on the equilibrium genetic variance, mutation load and inbreeding depression under stabilizing selection

10.1101/180000 ◽

2017 ◽

Author(s):

Diala Abu Awad ◽

Denis Roze

Keyword(s):

Inbreeding Depression ◽

Evolutionary Biology ◽

Genetic Variance ◽

Stabilizing Selection ◽

Genetic Associations ◽

Mutation Load ◽

Recombination Rates ◽

Self Fertilization ◽

Selected Traits ◽

Peer Community

ABSTRACTThis preprint has been reviewed and recommended by Peer Community In Evolutionary Biology (http://dx.doi.org/10.24072/pci.evolbiol.100041).The mating system of a species is expected to have important effects on its genetic diversity. In this paper, we explore the effects of partial selfing on the equilibrium genetic variance Vg, mutation load L and inbreeding depression δ under stabilizing selection acting on a arbitrary number n of quantitative traits coded by biallelic loci with additive effects. Overall, our model predicts a decrease in the equilibrium genetic variance with increasing selfing rates; however, the relationship between self-fertilization and the variables of interest depends on the strength of associations between loci, and three different regimes are observed. When the U/n ratio is low (where U is the total haploid mutation rate on selected traits) and effective recombination rates are sufficiently high, genetic associations between loci are negligible and the genetic variance, mutation load and inbreeding depression are well predicted by approximations based on single-locus models. For higher values of U/n and/or lower effective recombination, moderate genetic associations generated by epistasis tend to increase Vg, L and δ, this regime being well predicted by approximations including the effects of pairwise associations between loci. For yet higher values of U/n and/or lower effective recombination, a different regime is reached under which the maintenance of coadapted gene complexes reduces Vg, L and δ. Simulations indicate that the values of Vg, L and δ are little affected by assumptions regarding the number of possible alleles per locus.

The impact of self-incompatibility systems on the prevention of biparental inbreeding

PeerJ ◽

10.7717/peerj.4085 ◽

2017 ◽

Vol 5 ◽

pp. e4085

Author(s):

Tara N. Furstenau ◽

Reed A. Cartwright

Keyword(s):

Inbreeding Depression ◽

Pollen Dispersal ◽

Inbreeding Avoidance ◽

Self Incompatibility ◽

Origin And Evolution ◽

Biparental Inbreeding ◽

Self Fertilization ◽

Angiosperm Species ◽

Individual Based Simulation ◽

The Impact

Inbreeding in hermaphroditic plants can occur through two different mechanisms: biparental inbreeding, when a plant mates with a related individual, or self-fertilization, when a plant mates with itself. To avoid inbreeding, many hermaphroditic plants have evolved self-incompatibility (SI) systems which prevent or limit self-fertilization. One particular SI system—homomorphic SI—can also reduce biparental inbreeding. Homomorphic SI is found in many angiosperm species, and it is often assumed that the additional benefit of reduced biparental inbreeding may be a factor in the success of this SI system. To test this assumption, we developed a spatially-explicit, individual-based simulation of plant populations that displayed three different types of homomorphic SI. We measured the total level of inbreeding avoidance by comparing each population to a self-compatible population (NSI), and we measured biparental inbreeding avoidance by comparing to a population of self-incompatible plants that were free to mate with any other individual (PSI). Because biparental inbreeding is more common when offspring dispersal is limited, we examined the levels of biparental inbreeding over a range of dispersal distances. We also tested whether the introduction of inbreeding depression affected the level of biparental inbreeding avoidance. We found that there was a statistically significant decrease in autozygosity in each of the homomorphic SI populations compared to the PSI population and, as expected, this was more pronounced when seed and pollen dispersal was limited. However, levels of homozygosity and inbreeding depression were not reduced. At low dispersal, homomorphic SI populations also suffered reduced female fecundity and had smaller census population sizes. Overall, our simulations showed that the homomorphic SI systems had little impact on the amount of biparental inbreeding in the population especially when compared to the overall reduction in inbreeding compared to the NSI population. With further study, this observation may have important consequences for research into the origin and evolution of homomorphic self-incompatibility systems.

Mating system of Datura inoxia: association between selfing rates and herkogamy within populations

PeerJ ◽

10.7717/peerj.10698 ◽

2021 ◽

Vol 9 ◽

pp. e10698

Author(s):

Vania Jiménez-Lobato ◽

Juan Núñez-Farfán

Keyword(s):

Mating System ◽

Inbreeding Depression ◽

Selfing Rate ◽

Deleterious Alleles ◽

Mating System Evolution ◽

The Difference ◽

Selfing Syndrome ◽

Plant Mating System ◽

Datura Inoxia ◽

Plant Mating

Plant mating system determines, to a great extent, the demographic and genetic properties of populations, hence their potential for adaptive evolution. Variation in plant mating system has been documented between phylogenetically related species as well between populations of a species. A common evolutionary transition, from outcrossing to selfing, is likely to occur under environmental spatial variation in the service of pollinators. Here, we studied two phenotypically (in floral traits) and genetically (in neutral molecular markers) differentiated populations of the annual, insect-pollinated, plant Datura inoxia in Mexico, that differ in the service of pollinators (Mapimí and Cañada Moreno). First, we determined the populations’ parameters of phenotypic in herkogamy, outcrossing and selfing rates with microsatellite loci, and assessed between generation (adults and seedlings) inbreeding, and inbreeding depression. Second, we compared the relationships between parameters in each population. Results point strong differences between populations: plants in Mapimí have, on average, approach herkogamy, higher outcrossing rate (tm = 0.68), lower primary selfing rate (r = 0.35), and lower inbreeding at equilibrium (Fe = 0.24) and higher inbreeding depression (δ = 0.25), than the populations of Cañada. Outcrossing seems to be favored in Mapimí while selfing in Cañada. The relationship between r and Fe were negatively associated with herkogamy in Mapimí; here, progenies derived from plants with no herkogamy or reverse herkogamy had higher selfing rate and inbreeding coefficient than plants with approach herkogamy. The difference Fe–F is positively related to primary selfing rate (r) only in Cañada Moreno which suggests inbreeding depression in selfing individuals and then genetic purging. In conclusion, mating system evolution may occur differentially among maternal lineages within populations of Datura inoxia, in which approach herkogamy favors higher outcrossing rates and low levels of inbreeding and inbreeding depression, while no herkogamy or reverse herkogamy lead to the evolution of the “selfing syndrome” following the purge of deleterious alleles despite high inbreeding among individuals.

Multilocus models of inbreeding depression with synergistic selection and partial self-fertilization

Genetics Research ◽

10.1017/s0016672300029256 ◽

1991 ◽

Vol 57 (2) ◽

pp. 177-194 ◽

Cited By ~ 112

Author(s):

B. Charlesworth ◽

M. T. Morgan ◽

D. Charlesworth

Keyword(s):

Inbreeding Depression ◽

Mutation Rate ◽

Approximate Expression ◽

Heterozygote Advantage ◽

Selfing Rate ◽

Deleterious Alleles ◽

Plausible Model ◽

Computer Calculations ◽

Mean Fitness ◽

The Mean

SummaryMean fitness and inbreeding depression values in multi-locus models of the control of fitness were studied, using both a model of mutation to deleterious alleles, and a model of heterozygote advantage. Synergistic fitness interactions between loci were assumed, to find out if this more biologically plausible model altered the conclusions we obtained previously using a model of multiplicative interactions. Systems of unlinked loci were assumed. We used deterministic computer calculations, and approximations based on normal or Poisson theory. These approximations gave good agreement with the exact results for some regions of the parameter space. In the mutational model, we found that the effect of synergism was to lower the number of mutant alleles per individual, and thus to increase the mean fitness, compared with the multiplicative case. Inbreeding depression, however, was increased. Similar effects on mean fitness and inbreeding depression were found for the case of heterozygote advantage. For that model, the results were qualitatively similar to those previously obtained assuming multiplicativity. With the mutational load model, however, the mean fitness sometimes decreased, and the inbreeding depression increased, at high selfing rates, after declining as the selfing rate increased from zero. We also studied the behaviour of modifier alleles that changed the selfing rate, introduced into equilibrium populations. In general, the results were similar to those with the multiplicative model, but in some cases an ESS selfing rate, with selfing slightly below one, existed. Finally, we derive an approximate expression for the inbreeding depression in completely selfing populations. This depends only on the mutation rate and the dominance coefficient and can therefore be used to obtain estimates of the mutation rate to mildly deleterious alleles for plant species.

The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species

Genetics Research ◽

10.1017/s0016672399003845 ◽

1999 ◽

Vol 74 (1) ◽

pp. 31-42 ◽

Cited By ~ 59

Author(s):

J. RONFORT

Keyword(s):

Inbreeding Depression ◽

Deleterious Mutation ◽

Stable State ◽

Approximate Solutions ◽

Balance Model ◽

Deleterious Mutations ◽

Selfing Rate ◽

Mutation Load ◽

Mean Fitness ◽

The Mean

Single-locus equilibrium frequencies of a partially recessive deleterious mutation under the mutation–selection balance model are derived for partially selfing autotetraploid populations. Assuming multiplicative fitness interactions among loci, approximate solutions for the mean fitness and inbreeding depression values are also derived for the multiple locus case and compared with expectations for the diploid model. As in diploids, purging of deleterious mutations through consanguineous matings occurs in autotetraploid populations, i.e. the equilibrium mutation load is a decreasing function of the selfing rate. However, the variation of inbreeding depression with the selfing rate depends strongly on the dominance coefficients associated with the three heterozygous genotypes. Inbreeding depression can either increase or decrease with the selfing rate, and does not always vary monotonically. Expected issues for the evolution of the selfing rate consequently differ depending on the dominance coefficients. In some cases, expectations for the evolution of the selfing rate resemble expectations in diploids; but particular sets of dominance coefficients can be found that lead to either complete selfing or intermediate selfing rates as unique evolutionary stable state.