Sex chromosomes are highly variable in some taxonomic groups, but the evolutionary mechanisms underlying this diversity are not well understood. In terrestrial isopod crustaceans, evolutionary turnovers in sex chromosomes are frequent, possibly caused by Wolbachia, a vertically-transmitted endosymbiont causing male-to-female sex reversal. Here, we use surgical manipulations and genetic crosses, plus genome sequencing, to examine sex chromosomes in the terrestrial isopod Trachelipus rathkei. Although an earlier cytogenetics study suggested a ZZ/ZW sex chromosome system in this species, we surprisingly find multiple lines of evidence that in our study population, sex is determined by an XX/XY system. Consistent with a recent evolutionary origin for this XX/XY system, the putative male-specific region of the genome is small. The genome shows evidence of Y-linked duplications of the gene encoding the androgenic gland hormone, a major component of male sexual differentiation in isopods. Our analyses also uncover sequences horizontally acquired from past Wolbachia infections, consistent with the hypothesis that Wolbachia may have interfered with the evolution of sex determination in T. rathkei. Overall, these results provide evidence for the co-occurrence of multiple sex chromosome systems within T. rathkei, further highlighting the relevance of terrestrial isopods as models for the study of sex chromosome evolution.

性染色体在某些分类群中高度可变，但这种多样性背后的进化机制尚不清楚。在陆生等足类甲壳类动物中，性染色体的进化转换很频繁，这可能是由沃尔巴克氏体引起的，沃尔巴克氏体是一种垂直传播的内共生体，会导致雄性到雌性的性逆转。在这里，我们使用手术操作和遗传杂交以及基因组测序来检查陆生等足类动物Trachelipus rathkei中的性染色体. 尽管早期的细胞遗传学研究表明该物种存在 ZZ/ZW 性染色体系统，但我们令人惊讶地发现多条证据表明，在我们的研究人群中，性别由 XX/XY 系统决定。与此 XX/XY 系统的最近进化起源一致，基因组的假定男性特定区域很小。基因组显示编码雄性腺激素的基因存在 Y 连锁重复的证据，雄性腺激素是等足类动物雄性性分化的主要组成部分。我们的分析还揭示了从过去的Wolbachia感染中水平获得的序列，这与Wolbachia可能干扰了T. rathkei性别决定进化的假设一致. 总的来说，这些结果为T. rathkei中多个性染色体系统的共现提供了证据，进一步强调了陆生等足类动物作为性染色体进化研究模型的相关性。