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1.
Sexual differences are often dramatic and widespread across taxa. Their extravagance and ubiquity can be puzzling because the common underlying genome of males and females is expected to impede rather than foster phenotypic divergence. Widespread dimorphism, despite a shared genome, may be more readily explained by considering the multivariate, rather than univariate, framework governing the evolution of sexual dimorphism. In the univariate formulation, differences in genetic variances and a low intersexual genetic correlation () can facilitate the evolution of sexual dimorphism. However, studies that have analysed sex‐specific differences in heritabilities or genetic variances do not always find significant differences. Furthermore, many of the reported estimates of are very high and positive. When monomorphic heritabilities and a high are present together, the evolution of sexual dimorphism on a trait‐by‐trait basis is severely constrained. By contrast, the multivariate formulation has greater generality and more flexibility. Although the number of multivariate sexual dimorphism studies is low, almost all support sex‐specific differences in the G (variance‐covariance) matrix; G matrices can differ with respect to size and/or orientation, affecting the response to selection differently between the sexes. Second, whereas positive values of the univariate quantity only hinder positive changes in sexual dimorphism, positive covariances in the intersexual covariance B matrix can either help or hinder. Similarly, the handful of studies reporting B matrices indicate that it is often asymmetric, so that B can affect the evolution of single traits differently between the sexes. Multivariate approaches typically demonstrate that genetic covariances among traits can strongly constrain trait evolution when compared with univariate approaches. By contrast, in the evolution of sexual dimorphism, a multivariate view potentially reveals more opportunities for sexual dimorphism to evolve by considering the effect sex‐specific selection has on sex‐specific G matrices and an asymmetric B matrix. 相似文献
2.
Theory predicts that a 1 : 1 sex ratio is favoured in the absence of countervailing selection pressures. In an experiment with Drosophila melanogaster, we found significantly greater variation in the offspring sex ratios of freely mated flies than would be expected by the binomial distribution. In a surprise result, control flies given no mate choice exhibited significant under-dispersal in their sex ratio variation, possibly from sperm limitation. Both treatments, however, produced populations with a 1 : 1 sex ratio. This supports the hypothesis that sexually antagonistic selection for reproductive success in sons, and fecundity in daughters, may overcome selection for an equal sex ratio. Such precision in sex allocation may allow for the maintenance of genetic variation underlying trade-offs between male and female reproductive success. 相似文献
3.
Wyman MJ Cutter AD Rowe L 《Evolution; international journal of organic evolution》2012,66(5):1556-1566
Males and females share most of the same genes, so selection in one sex will typically produce a correlated response in the other sex. Yet, the sexes have evolved to differ in a multitude of behavioral, morphological, and physiological traits. How did this sexual dimorphism evolve despite the presence of a common underlying genome? We investigated the potential role of gene duplication in the evolution of sexual dimorphism. Because duplication events provide extra genetic material, the sexes each might use this redundancy to facilitate sex‐specific gene expression, permitting the evolution of dimorphism. We investigated this hypothesis at the genome‐wide level in Drosophila melanogaster, using the presence of sex‐biased expression as a proxy for the sex‐specific specialization of gene function. We expected that if sexually antagonistic selection is a potent force acting upon individual genes, duplication will result in paralog families whose members differ in sex‐biased expression. Gene members of the same duplicate family can have different expression patterns in males versus females. In particular, duplicate pairs containing a male‐biased gene are found more frequently than expected, in agreement with previous studies. Furthermore, when the singleton ortholog is unbiased, duplication appears to allow one of the paralog copies to acquire male‐biased expression. Conversely, female‐biased expression is not common among duplicates; fewer duplicate genes are expressed in the female‐soma and ovaries than in the male‐soma and testes. Expression divergence exists more in older than in younger duplicates pairs, but expression divergence does not correlate with protein sequence divergence. Finally, genomic proximity may have an effect on whether paralogs differ in sex‐biased expression. We conclude that the data are consistent with a role of gene duplication in fostering male‐biased, but not female‐biased, gene expression, thereby aiding the evolution of sexual dimorphism. 相似文献
4.
The Fisherian sexual selection paradigm has been called the null model of sexual selection. At its heart is the expectation of a genetic correlation (rG) between female preference and male trait. However, recent meta‐analysis has shown estimated correlations are often extremely weak and not statistically significant. We show here that systematic failure of studies to reject the null hypothesis that rG = 0 is almost certainly due to the low power of most experimental designs used. We provide an easy way to assess experimental power a priori and suggest that current data make it difficult to definitively test a key component of the Fisher effect. 相似文献
5.
Stronger selection on males has the potential to lower the deleterious mutation load of females, reducing the cost of sex. However, few studies have directly quantified the strength of selection for both sexes. As the magnitude of inbreeding depression (ID) is related to the strength of selection, we measured the cost of inbreeding for both males and females in a laboratory population of Drosophila melanogaster. Using a novel technique for inbreeding, we found significant ID for both juvenile viability and adult fitness in both sexes. The genetic variation responsible for this depression in fitness appeared to be recessive for adult fitness (h=0.11) and partially additive for juvenile viability (h=0.29). ID was identical across the sexes in terms of juvenile viability but was significantly more deleterious for males than females as adults, even though female X-chromosome homogamety should predispose them to a higher inbreeding load. We estimated the strength of selection on adult males to be 1.24 greater than on adult females, and this appears to be a consequence of selection arising from competition for mates. Combined with the generally positive intersexual genetic correlation for inbred lines, our results suggest that the mutation load of sexual females could be meaningfully reduced by stronger selection acting on males. 相似文献
6.
Because homologous traits of males and females are likely to have a common genetic basis, sex-specific selection (often resulting from sexual selection on one sex) may generate an evolutionary tug-of-war known as intralocus sexual conflict, which will constrain the adaptive divergence of the sexes. Theory suggests that intralocus sexual conflict can be mitigated through reduction of the intersexual genetic correlation (rMF), predicting negative covariation between rMF and sexual dimorphism. In addition, recent work showed that selection should favor reduced expression of alleles inherited from the opposite-sex parent (intersexual inheritance) in traits subject to intralocus sexual conflict. For traits under sexual selection in males, this should be manifested either in reduced maternal heritability or, when conflict is severe, in reduced heritability through the opposite-sex parent in offspring of both sexes. However, because we do not know how far these hypothesized evolutionary responses can actually proceed, the importance of intralocus sexual conflict as a long-term constraint on adaptive evolution remains unclear. In this study, we investigated the genetic architecture of sexual and nonsexual morphological traits in Prochyliza xanthostoma. The lowest rMF and greatest dimorphism were exhibited by two sexual traits (head length and antenna length) and, among all traits, the degree of sexual dimorphism was correlated negatively with rMF. Moreover, sexual traits exhibited reduced maternal heritabilities, and the most strongly dimorphic sexual trait (antenna length) was heritable only through the same-sex parent in offspring of both sexes. Our results support theory and suggest that intralocus sexual conflict can be resolved substantially by genomic adaptation. Further work is required to identify the proximate mechanisms underlying these patterns. 相似文献
7.
Theory predicts that sexual reproduction can increase population viability relative to asexual reproduction by allowing sexual selection in males to remove deleterious mutations from the population without large demographic costs. This requires that selection acts more strongly in males than females and that mutations affecting male reproductive success have pleiotropic effects on population productivity, but empirical support for these assumptions is mixed. We used the seed beetle Callosobruchus maculatus to implement a three‐generation breeding design where we induced mutations via ionizing radiation (IR) in the F0 generation and measured mutational effects (relative to nonirradiated controls) on an estimate of population productivity in the F1 and effects on sex‐specific competitive lifetime reproductive success (LRS) in the F2. Regardless of whether mutations were induced via F0 males or females, they had strong negative effects on male LRS, but a nonsignificant influence on female LRS, suggesting that selection is more efficient in removing deleterious alleles in males. Moreover, mutations had seemingly shared effects on population productivity and competitive LRS in both sexes. Thus, our results lend support to the hypothesis that strong sexual selection on males can act to remove the mutation load on population viability, thereby offering a benefit to sexual reproduction. 相似文献
8.
Tim Connallon Robert M. Cox Ryan Calsbeek 《Evolution; international journal of organic evolution》2010,64(6):1671-1682
Theory suggests that sex‐specific selection can facilitate adaptation in sexually reproducing populations. However, sexual conflict theory and recent experiments indicate that sex‐specific selection is potentially costly due to sexual antagonism: alleles harmful to one sex can accumulate within a population because they are favored in the other sex. Whether sex‐specific selection provides a net fitness benefit or cost depends, in part, on the relative frequency and strength of sexually concordant versus sexually antagonistic selection throughout a species’ genome. Here, we model the net fitness consequences of sex‐specific selection while explicitly considering both sexually concordant and sexually antagonistic selection. The model shows that, even when sexual antagonism is rare, the fitness costs that it imposes will generally overwhelm fitness benefits of sexually concordant selection. Furthermore, the cost of sexual antagonism is, at best, only partially resolved by the evolution of sex‐limited gene expression. To evaluate the key parameters of the model, we analyze an extensive dataset of sex‐specific selection gradients from wild populations, along with data from the experimental evolution literature. The model and data imply that sex‐specific selection may likely impose a net cost on sexually reproducing species, although additional research will be required to confirm this conclusion. 相似文献
9.
Schwander T Beukeboom LW 《BioEssays : news and reviews in molecular, cellular and developmental biology》2011,33(2):111-114
A new study in Caenorhabditis elegans shows that homologous autosomes segregate non-randomly with the sex chromosome in the heterogametic sex. Segregation occurs according to size, small autosomes segregating with, and large autosomes segregating away from the X-chromosome. Such sex-biased transmission of autosomes could facilitate the spread of sexually antagonistic alleles whose effects favor the fitness of one sex at the expense of the other. This may provide a first step toward the evolution of new sex determination systems. 相似文献
10.
Melissa A. Toups Nicolas Rodrigues Nicolas Perrin Mark Kirkpatrick 《Molecular ecology》2019,28(8):1877-1889
X and Y chromosomes can diverge when rearrangements block recombination between them. Here we present the first genomic view of a reciprocal translocation that causes two physically unconnected pairs of chromosomes to be coinherited as sex chromosomes. In a population of the common frog (Rana temporaria), both pairs of X and Y chromosomes show extensive sequence differentiation, but not degeneration of the Y chromosomes. A new method based on gene trees shows both chromosomes are sex‐linked. Furthermore, the gene trees from the two Y chromosomes have identical topologies, showing they have been coinherited since the reciprocal translocation occurred. Reciprocal translocations can thus reshape sex linkage on a much greater scale compared with inversions, the type of rearrangement that is much better known in sex chromosome evolution, and they can greatly amplify the power of sexually antagonistic selection to drive genomic rearrangement. Two more populations show evidence of other rearrangements, suggesting that this species has unprecedented structural polymorphism in its sex chromosomes. 相似文献
11.
The X chromosome is found twice as often in females as males. This has led to an intuition that X‐linked genes for traits experiencing sexually antagonistic selection should tend to evolve toward the female optimum. However, this intuition has never been formally examined. In this paper, I present a simple mathematical model and ask whether the X chromosome is indeed biased toward effecting female‐optimal phenotypes. Counter to the intuition, I find that the exact opposite bias exists; the X chromosome is revealed to be a welcome spot for mutations that benefit males at the expense of females. Not only do male‐beneficial alleles have an easier time of invading and spreading through a population, but they also achieve higher equilibrium frequencies than comparable female‐beneficial alleles. The X chromosome is therefore expected over evolutionary time to nudge phenotypes closer to the male optimum. Consequently, the X chromosome should find itself engaged in perpetual intragenomic conflicts with the autosomes and the mitochondria over developmental outcomes. The X chromosome's male bias and the intragenomic conflicts that ensue bear on the evolution of gene regulation, speciation, and our concept of organismality. 相似文献
12.
Steven A. Frank Manus M. Patten 《Evolution; international journal of organic evolution》2020,74(2):495-498
Males and females have different optimal values for some traits, such as body size. When the same genes control these traits in both sexes, selection pushes in opposite directions in males and females. Alleles at autosomal loci spend equal amounts of time in males and females, suggesting that the sexually antagonistic selective forces may approximately balance between the opposing optima. Frank and Crespi noted that alleles on the X chromosome spend twice as much time in diploid females as in haploid males. That distinction between the sexes may tend to favor X-linked genes that push more strongly toward the female optimum than the male optimum. The female bias of X-linked genes opposes the intermediate optimum of autosomal genes, potentially creating a difference between the direction of selection on traits favored by X chromosomes and autosomes. Patten has recently argued that explicit genetic assumptions about dominance and the relative magnitude of allelic effects may lead X-linked genes to favor the male rather than the female optimum, contradicting Frank and Crespi. This article combines the insights of those prior analyses into a new, more general theory. We find some parameter combinations for X-linked loci that favor a female bias and other parameter combinations that favor a male bias. We conclude that the X likely contains a mosaic pattern of loci that differ with autosomes over sexually antagonistic traits. The overall tendency for a female or male bias on the X depends on prior assumptions about the distribution of key parameters across X-linked loci. Those parameters include the dominance coefficient and the way in which ploidy influences the magnitude of allelic effects. 相似文献
13.
Knowledge of heritability and genetic correlations are of central importance in the study of adaptive trait evolution and genetic constraints. We use a paternal half-sib-full-sib breeding design to investigate the genetic architecture of three life-history and morphological traits in the seed beetle, Callosobruchus maculatus. Heritability was significant for all traits under observation and genetic correlations between traits (r(A)) were low. Interestingly, we found substantial sex-specific genetic effects and low genetic correlations between sexes (r(MF)) in traits that are only moderately (weight at emergence) to slightly (longevity) sexually dimorphic. Furthermore, we found an increased sire ([Formula: see text]) compared to dam ([Formula: see text]) variance component within trait and sex. Our results highlight that the genetic architecture even of the same trait should not be assumed to be the same for males and females. Furthermore, it raises the issue of the presence of unnoticed environmental effects that may inflate estimates of heritability. Overall, our study stresses the fact that estimates of quantitative genetic parameters are not only population, time, environment, but also sex specific. Thus, extrapolation between sexes and studies should be treated with caution. 相似文献
14.
Katrine K. Lund-Hansen Jessica K. Abbott Edward H. Morrow 《Evolution; international journal of organic evolution》2020,74(12):2703-2713
A handful of studies have investigated sexually antagonistic constraints on achieving sex-specific fitness optima, although exclusively through male-genome-limited evolution experiments. In this article, we established a female-limited X chromosome evolution experiment, where we used an X chromosome balancer to enforce the inheritance of the X through the matriline, thus removing exposure to male selective constraints. This approach eliminates the effects of sexually antagonistic selection on the X chromosome, permitting evolution toward a single sex-specific optimum. After multiple generations of selection, we found strong evidence that body size and development time had moved toward a female-specific optimum, whereas reproductive fitness and locomotion activity remained unchanged. The changes in body size and development time are consistent with previous results, and suggest that the X chromosome is enriched for sexually antagonistic genetic variation controlling these particular traits. The lack of change in reproductive fitness and locomotion activity could be due to a number of mutually nonexclusive explanations, including a lack of sexually antagonistic variance on the X chromosome for those traits or confounding effects of the use of the balancer chromosome. This study is the first to employ female-genome-limited selection and adds to the understanding of the complexity of sexually antagonistic genetic variation. 相似文献
15.
Tim Connallon Andrew G. Clark 《Evolution; international journal of organic evolution》2010,64(12):3417-3442
Sex‐biased genes—genes that are differentially expressed within males and females—are nonrandomly distributed across animal genomes, with sex chromosomes and autosomes often carrying markedly different concentrations of male‐ and female‐biased genes. These linkage patterns are often gene‐ and lineage‐dependent, differing between functional genetic categories and between species. Although sex‐specific selection is often hypothesized to shape the evolution of sex‐linked and autosomal gene content, population genetics theory has yet to account for many of the gene‐ and lineage‐specific idiosyncrasies emerging from the empirical literature. With the goal of improving the connection between evolutionary theory and a rapidly growing body of genome‐wide empirical studies, we extend previous population genetics theory of sex‐specific selection by developing and analyzing a biologically informed model that incorporates sex linkage, pleiotropy, recombination, and epistasis, factors that are likely to vary between genes and between species. Our results demonstrate that sex‐specific selection and sex‐specific recombination rates can generate, and are compatible with, the gene‐ and species‐specific linkage patterns reported in the genomics literature. The theory suggests that sexual selection may strongly influence the architectures of animal genomes, as well as the chromosomal distribution of fixed substitutions underlying sexually dimorphic traits. 相似文献
16.
Delph LF Steven JC Anderson IA Herlihy CR Brodie ED 《Evolution; international journal of organic evolution》2011,65(10):2872-2880
Genetic correlations between the sexes can constrain the evolution of sexual dimorphism and be difficult to alter, because traits common to both sexes share the same genetic underpinnings. We tested whether artificial correlational selection favoring specific combinations of male and female traits within families could change the strength of a very high between-sex genetic correlation for flower size in the dioecious plant Silene latifolia. This novel selection dramatically reduced the correlation in two of three selection lines in fewer than five generations. Subsequent selection only on females in a line characterized by a lower between-sex genetic correlation led to a significantly lower correlated response in males, confirming the potential evolutionary impact of the reduced correlation. Although between-sex genetic correlations can potentially constrain the evolution of sexual dimorphism, our findings reveal that these constraints come not from a simple conflict between an inflexible genetic architecture and a pattern of selection working in opposition to it, but rather a complex relationship between a changeable correlation and a form of selection that promotes it. In other words, the form of selection on males and females that leads to sexual dimorphism may also promote the genetic phenomenon that limits sexual dimorphism. 相似文献
17.
Chromosome fusion and fission are primary mechanisms of karyotype evolution. In particular, the fusion of a sex chromosome and an autosome has been proposed as a mechanism to resolve intralocus sexual antagonism. If sexual antagonism is common throughout the genome, we should expect to see an excess of fusions that join sex chromosomes and autosomes. Here, we present a null model that provides the probability of a sex chromosome autosome fusion, assuming all chromosomes have an equal probability of being involved in a fusion. This closed-form expression is applicable to both male and female heterogametic sex chromosome systems and can accommodate unequal proportions of fusions originating in males and females. We find that over 25% of all chromosomal fusions are expected to join a sex chromosome and an autosome whenever the diploid autosome count is fewer than 16, regardless of the sex chromosome system. We also demonstrate the utility of our model by analysing two contrasting empirical datasets: one from Drosophila and one from the jumping spider genus Habronattus. We find that in the case of Habronattus, there is a significant excess of sex chromosome autosome fusions but that in Drosophila there are far fewer sex chromosome autosome fusions than would be expected under our null model. 相似文献
18.
Gert Stulp Bram Kuijper Abraham P. Buunk Thomas V. Pollet Simon Verhulst 《Biology letters》2012,8(6):976-978
Intralocus sexual conflict (IASC) occurs when a trait under selection in one sex constrains the other sex from achieving its sex-specific fitness optimum. Selection pressures on body size often differ between the sexes across many species, including humans: among men individuals of average height enjoy the highest reproductive success, while shorter women have the highest reproductive success. Given its high heritability, IASC over human height is likely. Using data from sibling pairs from the Wisconsin Longitudinal Study, we present evidence for IASC over height: in shorter sibling pairs (relatively) more reproductive success (number of children) was obtained through the sister than through the brother of the sibling pair. By contrast, in average height sibling pairs most reproductive success was obtained through the brother relative to the sister. In conclusion, we show that IASC over a heritable, sexually dimorphic physical trait (human height) affects Darwinian fitness in a contemporary human population. 相似文献
19.
《Current biology : CB》2020,30(18):3617-3623.e3
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20.
Mimicry of non-rewarding flowers to rewarding flowers has been accepted as a strategy to improve pollination success in angiosperms. It has been proposed that this mechanism depends on whether potential pollinators can discriminate between the flowers. In this study, the intersexual mimicry and deceit pollination were studied in a threatened dioecious aquatic herb, Ottelia acuminata. Its female flowers resemble male flowers in morphology and odor compounds, to avoid discrimination by pollinators and outcompete male flowers in attracting the pollinators using stronger scents and bigger flowers. However, an obvious visit bias of its pollinator (Apis cerana) to male flowers was detected, suggesting that bees can distinguish the rewarding males from non-rewarding females. Although the deceit was not successful, pollination was not seriously undermined because pollen limitation was found to be low in the sampled natural population. We speculate that, due to “accidental” visits on female flowers and “mistake” pollinations, pollen limitation could be mitigated by a high frequency of pollen donors, and is correlated with the size and sex ratio of a population. Ottelia acuminata is a threatened dioecious aquatic herb. We suggest that developing multi-stakeholder coalitions should be encouraged to save the threatened edible and ornamental plant species in China. We hope this study could provide new insights into understanding of the role of intersexual mimicry in other flowering plants. 相似文献