The maintenance of sexual reproduction is a problem in evolutionary theory because, all else being equal, asexual populations have a twofold fitness advantage over their sexual counterparts and should rapidly outnumber a sexual population because every individual has the potential to reproduce. The twofold cost of sex exists because of anisogamy or gamete dimorphism-egg-producing females make a larger contribution to the zygote compared with the small contribution made by the sperm of males, but both males and females contribute 50% of the genes. Anisogamy also generates the conditions for sexual selection, a powerful evolutionary force that does not exist in asexual populations. The continued prevalence of sexual reproduction indicates that the 'all else being equal' assumption is incorrect. Here I show that sexual selection can mitigate or even eliminate the cost of sex. If sexual selection causes deleterious mutations to be more deleterious in males than females, then deleterious mutations are maintained at lower equilibrium frequency in sexual populations relative to asexual populations. The fitness of sexual females is higher than asexuals because there is no difference in the fecundity of sexual females and asexuals of the same genotype, but the equilibrium frequency of deleterious mutations is lower in sexual populations. The results are not altered by synergistic epistasis in males.

译文

在进化论中,有性生殖的维持是一个问题,因为在所有其他条件相同的情况下,无性生殖群体比性生殖群体具有双重的适应性优势,并且应该迅速超过性生殖群体,因为每个人都有繁殖的潜力。由于异型或配子二态性,存在双重性别成本-与男性精子的贡献相比,产生卵子的雌性对合子的贡献更大,但雄性和雌性都贡献了50% 基因。异婚也产生了性选择的条件,这是无性群体中不存在的强大进化力量。有性生殖的持续流行表明 “所有其他条件都相等” 的假设是不正确的。在这里,我表明性选择可以减轻甚至消除性行为的成本。如果性选择导致有害突变在男性中比在女性中更有害,那么相对于无性人群,有害突变在性人群中保持在较低的平衡频率。性女性的适应性高于无性女性,因为相同基因型的性女性和无性女性的繁殖力没有差异,但有性人群中有害突变的平衡频率较低。男性的协同上位性不会改变结果。

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