共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
The impact of directional selection on specific trait types in plant species, and how a species’ life history mediates this response to selection remains understudied. Discovering such interactions is however crucial for understanding the interplay between ecological and genetic processes underlying local adaptation in plants, and to evaluate a species’ evolutionary potential with respect to changing environments. Furthermore, it remains unclear whether the degree of adaptive differentiation generally increases with the geographical distance between plant populations. Here, we present a weighted mixed model based meta-analysis aimed at unraveling the potential interactions between plant trait types, life history characteristics and QST–FST comparisons, and assessing the effect of geographical scale on population differentiation. Based on 51 studies we found that QST values exceeded their corresponding FST values in 71.74 % out of 401 cases. Furthermore, different trait types were found to be differently susceptible to natural selection and the magnitude of QST–FST comparisons was mediated by a plant species’ life span. These findings may be closely related to the genetic architectures of trait types and life histories, with the proportion of large-effect genes likely shaping the response to natural selection. QST–FST values also increased with increasing distance between populations, pinpointing the combined effects of environmental differentiation and isolation by distance on the magnitude of population divergence. Finally, our model showed an inverse relationship between FST and QST–FST values, presumably resulting from isolation by distance, the exchange of advantageous alleles, or genetic correlations among traits. 相似文献
3.
Kin and levels-of-selection models are common approaches for modelling social evolution. Indirect genetic effect (IGE) models represent a different approach, specifying social effects on trait values rather than fitness. We investigate the joint effect of relatedness, multilevel selection and IGEs on response to selection. We present a measure for the degree of multilevel selection, which is the natural partner of relatedness in expressions for response. Response depends on both relatedness and the degree of multilevel selection, rather than only one or the other factor. Moreover, response is symmetric in relatedness and the degree of multilevel selection, indicating that both factors have exactly the same effect. Without IGEs, the key parameter is the product of relatedness and the degree of multilevel selection. With IGEs, however, multilevel selection without relatedness can explain evolution of social traits. Thus, next to relatedness and multilevel selection, IGEs are a key element in the genetical theory of social evolution. 相似文献
4.
Generalization of the QST framework in hierarchically structured populations: Impacts of inbreeding and dominance
下载免费PDF全文
![点击此处可从《Molecular ecology resources》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Philippe Cubry Ivan Scotti Sylvie Oddou‐Muratorio François Lefèvre 《Molecular ecology resources》2017,17(6):e76-e83
QST is a differentiation parameter based on the decomposition of the genetic variance of a trait. In the case of additive inheritance and absence of selection, it is analogous to the genic differentiation measured on individual loci, FST. Thus, QST?FST comparison is used to infer selection: selective divergence when QST > FST, or convergence when QST < FST. The definition of Q‐statistics was extended to two‐level hierarchical population structures with Hardy–Weinberg equilibrium. Here, we generalize the Q‐statistics framework to any hierarchical population structure. First, we developed the analytical definition of hierarchical Q‐statistics for populations not at Hardy–Weinberg equilibrium. We show that the Q‐statistics values obtained with the Hardy–Weinberg definition are lower than their corresponding F‐statistics when FIS > 0 (higher when FIS < 0). Then, we used an island model simulation approach to investigate the impact of inbreeding and dominance on the QST?FST framework in a hierarchical population structure. We show that, while differentiation at the lower hierarchical level (QSR) is a monotonic function of migration, differentiation at the upper level (QRT) is not. In the case of additive inheritance, we show that inbreeding inflates the variance of QRT, which can increase the frequency of QRT > FRT cases. We also show that dominance drastically reduces Q‐statistics below F‐statistics for any level of the hierarchy. Therefore, high values of Q‐statistics are good indicators of selection, but low values are not in the case of dominance. 相似文献
5.
G. M. Tallis P. Leppard 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1988,75(2):278-281
Communicated by A. Robertson 相似文献
6.
7.
Background selection, the effects of the continual removal of deleterious mutations by natural selection on variability at linked sites, is potentially a major determinant of DNA sequence variability. However, the joint effects of background selection and genetic recombination on the shape of the neutral gene genealogy have proved hard to study analytically. The only existing formula concerns the mean coalescent time for a pair of alleles, making it difficult to assess the importance of background selection from genome-wide data on sequence polymorphism. Here we develop a structured coalescent model of background selection with recombination and implement it in a computer program that efficiently generates neutral gene genealogies for an arbitrary sample size. We check the validity of the structured coalescent model against forward-in-time simulations and show that it accurately captures the effects of background selection. The model produces more accurate predictions of the mean coalescent time than the existing formula and supports the conclusion that the effect of background selection is greater in the interior of a deleterious region than at its boundaries. The level of linkage disequilibrium between sites is elevated by background selection, to an extent that is well summarized by a change in effective population size. The structured coalescent model is readily extendable to more realistic situations and should prove useful for analyzing genome-wide polymorphism data. 相似文献
8.
Background selection is a process whereby recurrent deleterious mutations cause a decrease in the effective population size and genetic diversity at linked loci. Several authors have suggested that variation in the intensity of background selection could cause variation in FST across the genome, which could confound signals of local adaptation in genome scans. We performed realistic simulations of DNA sequences, using recombination maps from humans and sticklebacks, to investigate how variation in the intensity of background selection affects FST and other statistics of population differentiation in sexual, outcrossing species. We show that, in populations connected by gene flow, Weir and Cockerham's (1984; Evolution, 38 , 1358) estimator of FST is largely insensitive to locus‐to‐locus variation in the intensity of background selection. Unlike FST, however, dXY is negatively correlated with background selection. Moreover, background selection does not greatly affect the false‐positive rate in FST outlier studies in populations connected by gene flow. Overall, our study indicates that background selection will not greatly interfere with finding the variants responsible for local adaptation. 相似文献
9.
Natural selection and the evoluation of dominance 总被引:2,自引:0,他引:2
10.
F. E. Wasserman C. Dowd B. A. Schlinger D. Byman S. P. Battista T. H. Kunz 《Bioelectromagnetics》1984,5(3):331-339
Seventeen birds from 12 flocks were exposed to microwave radiation under various combinations of power density and duration; three birds from two additional flocks served as sham-exposed controls. Experiments were conducted outdoors at Manomet, Massachusetts (41°56′N, 70°35′W) under normal winter ambient temperatures. Although irradiated birds maintained their positions within a flock hierarchy with one exception, some appeared to have a change in their level of aggression after exposure. 相似文献
11.
Modification of dominance by selection in the homozygote 总被引:1,自引:0,他引:1
12.
Using the structured coalescent model, it is shown that unequal migration rates between different pairs of subpopulations can increase the value of Wright's coefficient F(ST) and its dependence on the mutation rate, and decrease the effective level of gene flow. Two specific models of population structure are considered: (i) an 'island model with barrier' where migration rates between subpopulations on the same side of the barrier are higher than migration rates between subpopulations on opposite sides of the barrier, and (ii) the two-dimensional stepping-stone model with unequal migration rates in the two dimensions of the model. 相似文献
13.
Most models of positive directional selection assume codominance of the beneficial allele. We examine the importance of this assumption by implementing a coalescent model of positive directional selection with arbitrary dominance. We find that, for a given mean fixation time, a beneficial allele has a much weaker effect on diversity at linked neutral sites when the allele is recessive. 相似文献
14.
The evolution of dominance: a direct approach through the theory of linkage and selection 总被引:5,自引:1,他引:4
The mathematical model of evolution of dominance proposed by Fisher and Wright, and expanded upon by Ewens and others is subjected to a more thorough examination. The model is treated as a bonafide two locus system of a major and modifying locus involving mutation, selection and recombination. In the usual case we confirm Ewens' conclusion to the effect that in the final stages the rate of evolution is essentially algebraic. Further, we establish the role of linkage in determining the rate of evolution. Specifically we show that in both the initial and final stages of the process the looser the linkage the faster the progress towards complete dominance. 相似文献
15.
Response to joint selection on germination and flowering phenology depends on the direction of selection
下载免费PDF全文
![点击此处可从《Ecology and evolution》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Flowering and germination time are components of phenology, a complex phenotype that incorporates a number of traits. In natural populations, selection is likely to occur on multiple components of phenology at once. However, we have little knowledge of how joint selection on several phenological traits influences evolutionary response. We conducted one generation of artificial selection for all combinations of early and late germination and flowering on replicated lines within two independent base populations in the herb Campanula americana. We then measured response to selection and realized heritability for each trait. Response to selection and heritability were greater for flowering time than germination time, indicating greater evolutionary potential of this trait. Selection for earlier phenology, both flowering and germination, did not depend on the direction of selection on the other trait, whereas response to selection to delay germination and flowering was greater when selection on the other trait was in the opposite direction (e.g., early germination and late flowering), indicating a negative genetic correlation between the traits. Therefore, the extent to which correlations shaped response to selection depended on the direction of selection. Furthermore, the genetic correlation between timing of germination and flowering varies across the trait distributions. The negative correlation between germination and flowering time found when selecting for delayed phenology follows theoretical predictions of constraint for traits that jointly determine life history schedule. In contrast, the lack of constraint found when selecting for an accelerated phenology suggests a reduction of the covariance due to strong selection favoring earlier flowering and a shorter life cycle. This genetic architecture, in turn, will facilitate further evolution of the early phenology often favored in warm climates. 相似文献
16.
Bystander effects and the structure of dominance hierarchies 总被引:6,自引:1,他引:5
Prior modeling work has found that pure winner and loser effects(i.e., changing the estimation of your own fighting abilityas a function of direct prior experience) can have importantconsequences for hierarchy formation. Here these models areextended to incorporate "bystander effects." When bystandereffects are in operation, observers (i.e., bystanders) of aggressiveinteractions change their assessment of the protagonists' fighting
abilities (depending on who wins and who loses). Computer simulations
demonstrate that when bystander winner effects alone are atplay, groups have a clear omega (bottom-ranking individual),while the relative position of other group members remainsdifficult to determine. When only bystander loser effects arein operation, wins and losses are randomly distributed throughout
a group (i.e., no discernible hierarchy). When pure and bystanderwinner effects are jointly in place, a linear hierarchy, inwhich all positions (i.e., to when N = 4) are clearly defined,emerges. Joint pure and bystander loser effects produce thesame result. In principle one could test the predictions fromthe models developed here in a straightforward comparativestudy. Hopefully, the results of this model will spur on suchstudies in the future. 相似文献
17.
Deleterious alleles are constantly introduced into populations due to mutation. In subdivided populations, the impact of these mutations depends on the strength of selection as well as the softness of selection, that is, the extent to which fitness is governed by local rather than global competition. It is widely appreciated that the intensity and type of competition will affect selection on deleterious mutations but most empirical work has focused solely on the effects of competition on selection strength. However, competition has rarely been studied in the context of selection ‘softness’ even though competition is at the conceptual root of soft selection. All other things being equal, theory predicts that inter‐ and intraspecific competitions have opposing effects on the softness of selection. Using Drosophila melanogaster, we estimated the strength and softness of selection in a ‘baseline’ competitive environment as well as two additional competitive environments characterized by either additional intra‐ or interspecific competitors. We found that competitive environment had little effect on the average strength of selection. While the softness of selection was affected by the type of competition, the direction of change varied across tests of different genes, contrary to expectation. Although the ‘hard/soft’ selection paradigm implicitly assumes that all individuals are equally sensitive to the local competitive environment, we found this not to be the case. Wild‐type individuals were more sensitive to changes in the genetic quality of their local competitors than mutant individuals. 相似文献
18.
Naoyuki Takahata 《Theoretical population biology》1982,22(2):258-277
The advantage or disadvantage of sexual reproduction or recombination for the accumulation of mutant genes in a population is studied under the joint effects of recurrent mutations, selection, and random sampling drift. To obtain the rate at which mutant genes are incorporated three different methods are used; numerical integration of Kolmogorov backward equations, simulation of stochastic difference equations, and Monte Carlo experiments. The first two methods are used in a two-locus system to obtain the fixation probability of double mutants and other related quantities under five different selection models. The third one is conducted for a multiple-locus system and the rate of accumulation of mutant genes per locus is studied. Comparison of the results between sexual and asexual populations shows that the effect of recombination depends on initial linkage disequilibrium, mutation rate v, selection intensity s, and population size Ne. The mode of selection is also an important factor and the large effect of recombination is observed when mutant genes are individually deleterious but collectively favorable. Under a given model of selection, the great advantage or disadvantage of recombination is achieved when a large extent of genetic polymorphism is produced not by mutation but by recombination. Extreme values of Nes and Nev make the effect insignificant. The results of Monte Carlo experiments also reveal the presence of interaction between selection and sampling drift even when the loci segregate independently and selection is multiplicative. Although this interaction is usually small, there are cases in which one locus theory cannot be used freely. In those cases, the effect of recombination is prominent and one locus theory gives an overestimate of the rate. 相似文献
19.
FST is frequently used as a summary of genetic differentiation among groups. It has been suggested that FST depends on the allele frequencies at a locus, as it exhibits a variety of peculiar properties related to genetic diversity: higher values for biallelic single-nucleotide polymorphisms (SNPs) than for multiallelic microsatellites, low values among high-diversity populations viewed as substantially distinct, and low values for populations that differ primarily in their profiles of rare alleles. A full mathematical understanding of the dependence of FST on allele frequencies, however, has been elusive. Here, we examine the relationship between FST and the frequency of the most frequent allele, demonstrating that the range of values that FST can take is restricted considerably by the allele-frequency distribution. For a two-population model, we derive strict bounds on FST as a function of the frequency M of the allele with highest mean frequency between the pair of populations. Using these bounds, we show that for a value of M chosen uniformly between 0 and 1 at a multiallelic locus whose number of alleles is left unspecified, the mean maximum FST is ∼0.3585. Further, FST is restricted to values much less than 1 when M is low or high, and the contribution to the maximum FST made by the most frequent allele is on average ∼0.4485. Using bounds on homozygosity that we have previously derived as functions of M, we describe strict bounds on FST in terms of the homozygosity of the total population, finding that the mean maximum FST given this homozygosity is 1 − ln 2 ≈ 0.3069. Our results provide a conceptual basis for understanding the dependence of FST on allele frequencies and genetic diversity and for interpreting the roles of these quantities in computations of FST from population-genetic data. Further, our analysis suggests that many unusual observations of FST, including the relatively low FST values in high-diversity human populations from Africa and the relatively low estimates of FST for microsatellites compared to SNPs, can be understood not as biological phenomena associated with different groups of populations or classes of markers but rather as consequences of the intrinsic mathematical dependence of FST on the properties of allele-frequency distributions.DIFFERENTIATION among groups is one of the fundamental subjects of the field of population genetics. Comparisons of the level of variation among subpopulations with the level of variation in the total population have been employed frequently in population-genetic theory, in statistical methods for data analysis, and in empirical studies of distributions of genetic variation. Wright’s (Wright 1951) fixation indices, and FST in particular, have been central to this effort.Wright’s FST was originally defined as the correlation between two randomly sampled gametes from the same subpopulation when the correlation of two randomly sampled gametes from the total population is set to zero. Several definitions of FST or FST-like quantities are now available, relying on a variety of different conceptual formulations but all measuring some aspect of population differentiation (e.g., Charlesworth 1998; Holsinger and Weir 2009). Many authors have claimed that one or another formulation of FST is affected by levels of genetic diversity or by allele frequencies, either because the range of FST is restricted by these quantities or because these quantities affect the degree to which FST reflects population differentiation (e.g., Charlesworth 1998; Nagylaki 1998; Hedrick 1999, 2005; Long and Kittles 2003; Jost 2008; Ryman and Leimar 2008; Long 2009; Meirmans and Hedrick 2011). For example, Nagylaki (1998) and Hedrick (1999) argued that measures of FST may be poor measures of genetic differentiation when the level of diversity is high. Charlesworth (1998) suggested that FST can be inflated when diversity is low, arguing that FST might not be appropriate for comparing loci with substantially different levels of variation. In a provocative recent article, Jost (2008) used the diversity dependence of forms of FST to question their utility as differentiation measures at all.One definition that is convenient for mathematical assessment of the relationship of an FST-like quantity and allele frequencies is the quantity labeled GST by Nei (1973), which for a given locus measures the difference between the heterozygosity of the total (pooled) population, hT, and the mean heterozygosity across subpopulations, hS, divided by the heterozygosity of the total population:(1)In terms of the homozygosity of the total population, HT = 1 − hT, and the mean homozygosity across subpopulations, HS = 1 − hS, we can write(2)The Wahlund (1928) principle guarantees that HS ≥ HT and, therefore, because HS ≤ 1 and for a polymorphic locus with finitely many alleles, 0 < HT < 1, GST lies in the interval [0,1].Using GST for their definition of FST, Hedrick (1999, 2005) and Long and Kittles (2003) pointed out that because hT < 1, FST cannot exceed the mean homozygosity across subpopulations, HS:FST = 1 ? hS/hT < 1 ? hS = HS.(3)Hedrick (2005) obtained this result by considering a set of K equal-sized subpopulations, in which each allele is private to a single subpopulation. In the limit as K → ∞, a stronger upper bound on FST as a function of HS and K reduces to Equation 3 (see also Jin and Chakraborty 1995 and Long and Kittles 2003).While Hedrick (1999, 2005) and Long and Kittles (2003) have clarified the relationship between FST and the mean homozygosity HS across subpopulations, their approaches do not easily illuminate the connection between FST and allele frequencies themselves. A formal understanding of the relationship between FST and allele frequencies would make it possible to more fully understand the behavior of FST in situations where markers of interest differ substantially in allele frequencies or levels of genetic diversity. Our recent work on the relationship between homozygosity and the frequency of the most frequent allele (Rosenberg and Jakobsson 2008; Reddy and Rosenberg 2012) provides a mathematical approach for formal investigation of bounds on population-genetic statistics in terms of allele frequencies. In this article, we therefore seek to thoroughly examine the dependence of FST on allele frequencies by investigating the upper bound on FST in terms of the frequency M of the most frequent allele across a pair of populations. We derive bounds on FST given the frequency of the most frequent allele and bounds on the frequency of the most frequent allele given FST. We consider loci with arbitrarily many alleles in a pair of subpopulations. Using theory for the bounds on homozygosity given the frequency of the most frequent allele, we obtain strict bounds on FST given the homozygosity of the total population. Our analysis clarifies the relationships among FST, allele frequencies, and homozygosity, providing explanations for peculiar observations of FST that can be attributed to allele-frequency dependence. 相似文献
20.
Male red-winged blackbirds were given implants of testosterone or flutamide in order to manipulate the level of androgen reaching receptor sites. Implants of cholesterol were given as controls. Radioimmunoassay showed higher levels of testosterone and DHT in the plasma of testosterone-implanted birds than in the plasma of the pooled flutamide-implanted and cholesterol-implanted birds. Dominance was significantly correlated with effective androgen level. Androgen level was not correlated with rates of supplantations per subordinate but was correlated with rates of escalated attacks per subordinate. Thus androgen level influences dominance in male red-winged blackbirds by influencing one component of aggressiveness. 相似文献