Sex strongly impacts genome evolution via recombination and segregation. In the absence of these processes, haplotypes within lineages of diploid organisms are predicted to accumulate mutations independently of each other and diverge over time. This so-called “Meselson effect” is regarded as a strong indicator of the long-term evolution under obligate asexuality. Here, we present genomic and transcriptomic data of three populations of the asexual oribatid mite species Oppiella nova and its sexual relative Oppiella subpectinata. We document strikingly different patterns of haplotype divergence between the two species, strongly supporting Meselson effect–like evolution and long-term asexuality in O. nova: I) variation within individuals exceeds variation between populations in O. nova but vice versa in O. subpectinata; II) two O. nova sublineages feature a high proportion of lineage-specific heterozygous single-nucleotide polymorphisms (SNPs), indicating that haplotypes continued to diverge after lineage separation; III) the deepest split in gene trees generally separates the two haplotypes in O. nova, but populations in O. subpectinata; and IV) the topologies of the two haplotype trees match each other. Our findings provide positive evidence for the absence of canonical sex over evolutionary time in O. nova and suggest that asexual oribatid mites can escape the dead-end fate usually associated with asexual lineages.

性别通过重组和分离强烈影响基因组进化。在没有这些过程的情况下，预计二倍体生物谱系内的单倍型会彼此独立地积累突变，并随着时间的推移而发生分化。这种所谓的“梅塞尔森效应”被认为是专性无性生殖下长期进化的有力指标。在这里，我们展示了无性螨类Oppiella nova及其有性亲属Oppiella subpectinata三个种群的基因组和转录组数据。我们记录了两个物种之间显着不同的单倍型分化模式，强烈支持O. nova中的类似梅塞尔森效应的进化和长期无性行为：I) O. nova中个体内部的变异超过了群体之间的变异，但O. subpectinata中反之亦然; II) 两个O. nova亚谱系具有高比例的谱系特异性杂合单核苷酸多态性 (SNP)，表明谱系分离后单倍型继续分化； III) 基因树中最深的分裂通常将O. nova中的两个单倍型分开，但O. subpectinata中的群体; IV) 两个单倍型树的拓扑相互匹配。我们的研究结果为O. nova在进化过程中不存在规范性性别提供了积极的证据，并表明无性生殖螨可以逃脱通常与无性谱系相关的死胡同命运。