Despite its inherent costs, sexual reproduction is ubiquitous in nature, and the mechanisms to protect it from a competitive displacement by asexuality remain unclear. Popular mutation‐based explanations, like the Muller's ratchet and the Kondrashov's hatchet, assume that purifying selection may not halt the accumulation of deleterious mutations in the nonrecombining genomes, ultimately leading to their degeneration. However, empirical evidence is scarce and it remains particularly unclear whether mutational degradation proceeds fast enough to ensure the decay of clonal organisms and to prevent them from outcompeting their sexual counterparts. To test this hypothesis, we jointly analysed the exome sequences and the fitness‐related phenotypic traits of the sexually reproducing fish species and their clonal hybrids, whose evolutionary ages ranged from F1 generations to 300 ky. As expected, mutations tended to accumulate in the clonal genomes in a time‐dependent manner. However, contrary to the predictions, we found no trend towards increased nonsynonymity of mutations acquired by clones, nor higher radicality of their amino acid substitutions. Moreover, there was no evidence for fitness degeneration in the old clones compared with that in the younger ones. In summary, although an efficacy of purifying selection may still be reduced in the asexual genomes, our data indicate that its efficiency is not drastically decreased. Even the oldest investigated clone was found to be too young to suffer fitness consequences from a mutation accumulation. This suggests that mechanisms other than mutation accumulation may be needed to explain the competitive advantage of sex in the short term.

中文翻译：

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没有证据表明克隆鱼杂种中有害突变的积累和适应性降低：放弃性生活不后悔。

尽管有其固有的成本，但性生殖在自然界还是普遍存在的，尚不清楚保护性生殖免受无性竞争取代的机制。流行的基于突变的解释，例如穆勒的棘轮和康达拉索夫的斧头，认为纯化选择可能不会阻止非重组基因组中有害突变的积累，最终导致它们的退化。但是，缺乏经验证据，尤其不清楚的是突变降解的进行速度是否足够快，以确保克隆生物的腐烂并阻止其竞争性伴侣。为了验证这一假设，我们共同分析了有性繁殖鱼类及其克隆杂种的外显子组序列和与健身相关的表型特征，其进化年龄从F1代到300 ky。如预期的那样，突变倾向于以时间依赖的方式在克隆基因组中积累。然而，与预测相反，我们没有发现克隆获得的突变的非同义性增加的趋势，也没有发现其氨基酸取代的更高自由基性的趋势。此外，与年轻的克隆相比，没有证据表明老克隆具有适合性退化。总而言之，尽管无性基因组中纯化选择的功效可能仍会降低，但我们的数据表明其功效并未急剧降低。即使是研究最久的克隆，也发现其年龄太小，无法承受突变积累带来的适应性后果。