Brandt Alexander, Schaefer Ina, Glanz Julien, Schwander Tanja, Maraun Mark, Scheu Stefan, Bast Jens
Johann-Friedrich-Blumenbach Institute of Zoology and Anthropology, Georg-August-University Goettingen, Untere Karspuele 2, DE-37073, Goettingen, Germany.
Department of Ecology and Evolution, University of Lausanne, UNIL Sorge, Le Biophore, CH-1015, Lausanne, Switzerland.
Nat Commun. 2017 Oct 12;8(1):873. doi: 10.1038/s41467-017-01002-8.
Sex is beneficial in the long term because it can prevent mutational meltdown through increased effectiveness of selection. This idea is supported by empirical evidence of deleterious mutation accumulation in species with a recent transition to asexuality. Here, we study the effectiveness of purifying selection in oribatid mites which have lost sex millions of years ago and diversified into different families and species while reproducing asexually. We compare the accumulation of deleterious nonsynonymous and synonymous mutations between three asexual and three sexual lineages using transcriptome data. Contrasting studies of young asexual lineages, we find evidence for strong purifying selection that is more effective in asexual as compared to sexual oribatid mite lineages. Our results suggest that large populations likely sustain effective purifying selection and facilitate the escape of mutational meltdown in the absence of sex. Thus, sex per se is not a prerequisite for the long-term persistence of animal lineages.Asexual reproduction is thought to be an evolutionary dead end in eukaryotes because deleterious mutations will not be purged effectively. Here, Brandt and colleagues show that anciently asexual oribatid mites in fact have reduced accumulation of deleterious mutations compared to their sexual relatives.
从长远来看，有性生殖是有益的，因为它可以通过提高选择效率来防止突变崩溃。这一观点得到了近期转变为无性生殖的物种中有害突变积累的经验证据的支持。在这里，我们研究了数百万年前就已失去有性生殖能力，并在无性繁殖过程中分化成不同科和物种的甲螨中纯化选择的有效性。我们使用转录组数据比较了三个无性谱系和三个有性谱系中有害非同义突变和同义突变的积累情况。与对年轻无性谱系的对比研究不同，我们发现了有力的纯化选择证据，在甲螨谱系中，无性谱系的纯化选择比有性谱系更有效。我们的研究结果表明，在没有有性生殖的情况下，大量种群可能维持有效的纯化选择，并有助于避免突变崩溃。因此，有性生殖本身并不是动物谱系长期存续的先决条件。在真核生物中，无性生殖被认为是一条进化的死胡同，因为有害突变无法得到有效清除。然而，布兰特及其同事的研究表明，与有性生殖的近亲相比，古老的无性甲螨实际上有害突变的积累有所减少。
