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

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.

Long-term Evolution, Short-term Evolution, and Population Genetic Theory

1998 ◽  
Vol 191 (4) ◽  
pp. 391-396 ◽  
Author(s):  
Ilan Eshel ◽  
Marcus W. Feldman ◽  
Aviv Bergman
Keyword(s):  
Population Genetic ◽  
Long Term Evolution ◽  
Short Term ◽  
Genetic Theory ◽  
Term Evolution

scholarly journals Epistasis, inbreeding depression and the evolution of self-fertilization

2019 ◽  
Author(s):  
Diala Abu Awad ◽  
Denis Roze
Keyword(s):  
Inbreeding Depression ◽  
Stabilizing Selection ◽  
Linkage Disequilibria ◽  
Deleterious Alleles ◽  
Mating System Evolution ◽  
Special Cases ◽  
Self Fertilization ◽  
Mean Fitness ◽  
Selection For ◽  
Individual Based Simulation

ABSTRACTInbreeding depression resulting from partially recessive deleterious alleles is thought to be the main genetic factor preventing self-fertilizing mutants from spreading in outcrossing hermaphroditic populations. However, deleterious alleles may also generate an advantage to selfers in terms of more efficient purging, while the effects of epistasis among those alleles on inbreeding depression and mating system evolution remain little explored. In this paper, we use a general model of selection to disentangle the effects of different forms of epistasis (additive-by-additive, additive-by-dominance and dominance-by-dominance) on inbreeding depression and on the strength of selection for selfing. Models with fixed epistasis across loci, and models of stabilizing selection acting on quantitative traits (generating distributions of epistasis) are considered as special cases. Besides its effects on inbreeding depression, epistasis may increase the purging advantage associated with selfing (when it is negative on average), while the variance in epistasis favors selfing through the generation of linkage disequilibria that increase mean fitness. Approximations for the strengths of these effects are derived, and compared with individual-based simulation results.

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

2019 ◽  
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.

Differences in morphology, survival and size between self- and cross-fertilized larvae of Mytilus galloprovincialis

1994 ◽  
Vol 74 (2) ◽  
pp. 445-448 ◽  
Author(s):  
A.R. Beaumont ◽  
A.K.M. Matin-Abdul
Keyword(s):  
Inbreeding Depression ◽  
Mytilus Galloprovincialis ◽  
Morphological Abnormality ◽  
Lower Survival ◽  
Self Fertilization ◽  
Cross Fertilization

The serendipitous detection of a rare hermaphrodite individual of Mytilus galloprovincialis during the process of spawning in the laboratory enabled self- and cross-fertilization to be achieved. Self-fertilized larvae exhibited significantly higher percentages of morphological abnormality at 3 d, lower survival at 9 d and decreased size at 31 d of age compared with cross-fertilized larvae. These results are discussed in the light of equivocal evidence for inbreeding depression in larvae derived from self-fertilization, full-sib matings and gynogenesis in other bivalves.

scholarly journals Selection Response in Finite Populations

Genetics ◽  
1996 ◽  
Vol 144 (4) ◽  
pp. 1961-1974 ◽  
Author(s):  
Ming Wei ◽  
Armando Caballero ◽  
William G Hill
Keyword(s):  
Linkage Disequilibrium ◽  
Inbreeding Depression ◽  
Genetic Variance ◽  
Relative Rate ◽  
Selection Response ◽  
Rate Of Change ◽  
Effective Population ◽  
Short Term ◽  
Model Account

Formulae were derived to predict genetic response under various selection schemes assuming an infinitesimal model. Account was taken of genetic drift, gametic (linkage) disequilibrium (Bulmer effect), inbreeding depression, common environmental variance, and both initial segregating variance within families (σAW02) and mutational (σM2) variance. The cumulative response to selection until generation t(CRt) can be approximated asCRt≈R0[t−β(1−σAW∞2σAW02)t24Ne]−Dt2Ne,where Ne is the effective population size, σAW∞2=NeσM2 is the genetic variance within families at the steady state (or one-half the genic variance, which is unaffected by selection), and D is the inbreeding depression per unit of inbreeding. R  0 is the selection response at generation 0 assuming preselection so that the linkage disequilibrium effect has stabilized. β is the derivative of the logarithm of the asymptotic response with respect to the logarithm of the within-family genetic variance, i.e., their relative rate of change. R  0 is the major determinant of the short term selection response, but σM2, Ne and β are also important for the long term. A selection method of high accuracy using family information gives a small Ne and will lead to a larger response in the short term and a smaller response in the long term, utilizing mutation less efficiently.

scholarly journals Stirred but not shaken: population and recruitment genetics of the scallop (Pecten fumatus) in Bass Strait, Australia

2016 ◽  
Vol 73 (9) ◽  
pp. 2333-2341 ◽  
Author(s):  
Jennifer R. Ovenden ◽  
Bree J. Tillett ◽  
Michael Macbeth ◽  
Damien Broderick ◽  
Fiona Filardo ◽  
...  
Keyword(s):  
Genetic Structure ◽  
Population Genetic Structure ◽  
Population Genetic ◽  
Allelic Variation ◽  
Open Water ◽  
Marine Species ◽  
Population Connectivity ◽  
Valuable Insight ◽  
Fine Scale ◽  
Scale Population

Abstract We report population genetic structure and fine-scale recruitment processes for the scallop beds (Pecten fumatus) in Bass Strait and the eastern coastline of Tasmania in southern Australia. Conventional population pairwise FST analyses are compared with novel discriminant analysis of principal components (DAPC) to assess population genetic structure using allelic variation in 11 microsatellite loci. Fine-scale population connectivity was compared with oceanic features of the sampled area. Disjunct scallop beds were genetically distinct, but there was little population genetic structure between beds connected by tides and oceanic currents. To identify recruitment patterns among and within beds, pedigree analyses determined the distribution of parent–offspring and sibling relationships in the sampled populations. Beds in northeastern Bass Strait were genetically distinct to adjacent beds (FST 0.003–0.005) and may not contribute to wider recruitment based on biophysical models of larval movement. Unfortunately, pedigree analyses lacked power to further dissect fine-scale recruitment processes including self-recruitment. Our results support the management of disjunct populations as separate stocks and the protection of source populations among open water beds. The application of DAPC and parentage analyses in the current study provided valuable insight into their potential power to determine population connectivity in marine species with larval dispersal.

scholarly journals Selection, Load and Inbreeding Depression in a Large Metapopulation

Genetics ◽  
2002 ◽  
Vol 160 (3) ◽  
pp. 1191-1202 ◽  
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.

Selection by parasites for clonal diversity and mixed mating

1994 ◽  
Vol 346 (1317) ◽  
pp. 271-281 ◽  
Keyword(s):  
Computer Simulations ◽  
Inbreeding Depression ◽  
Reproductive Strategies ◽  
Deleterious Mutation ◽  
Clonal Diversity ◽  
Evolutionary Stability ◽  
Mixed Mating ◽  
Dioecious Populations ◽  
Cross Fertilization ◽  
Evolutionarily Stable

On theoretical grounds, coevolutionary interactions with parasites can select for cross-fertilization, even when there is a twofold advantage gained by reproducing through uniparental means. The suspected advantage of cross-fertilization stems from the production of genetically rare offspring, which are expected to be more likely to escape infection by coevolving enemies. In the present study, we consider the effects that parasites have on parthenogenetic mutants in obligately sexual, dioecious populations. Computer simulations show that repeated mutation to parthenogenesis can lead to the accumulation of clones with different resistance genotypes, and that a moderately diverse set of clones could competitively exclude the ancestral sexual subpopulation. The simulations also show that, when there are reasonable rates of deleterious mutation, Muller’s ratchet combined with coevolutionary interactions with parasites can lead to the evolutionary stability of cross-fertilization. In addition, we consider the effects that parasites can have on the evolution of uniparental reproduction in cosexual populations. Strategy models show that parasites and inbreeding depression could interact to select for evolutionarily stable reproductive strategies that involve mixtures of selfed and outcrossed progeny.

Population Genetic Theory of the Cost of Inbreeding

1984 ◽  
Vol 123 (5) ◽  
pp. 642-653 ◽  
Author(s):  
Marcus Feldman ◽  
Freddy B. Christiansen
Keyword(s):  
Population Genetic ◽  
Genetic Theory ◽  
The Cost
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