Long-term experimental hybridisation results in a heterologous transition and the evolution of a new sex chromosome in swordtail fish

The remarkable diversity of sex determination mechanisms known in fish may be fuelled by exceptionally high rates of sex chromosome turnovers or transitions. However, the evolutionary causes and genomic mechanisms underlying this variation and instability are yet to be understood. Here we report on an over 30-year evolutionary experiment in which we tested the genomic consequences of hybridisation and selection between two Xiphophorus fish species with different sex chromosome systems. We find that introgression and imposing selection for pigmentation phenotypes results in the retention of an unexpectedly large maternally derived genomic region. During the hybridisation process, the sex-determining region of the X chromosome from one parental species was translocated to an autosome in the hybrids leading to the evolution of a new sex chromosome. Our results highlight the complexity of factors contributing to patterns observed in hybrid genomes, and we experimentally demonstrate that hyb...目前已知鱼类的性别决定机制具有极高的多样性，这或许源于性染色体更替（sex chromosome turnover）与转变的超高速率。然而，支撑这种变异与不稳定性的进化动因及基因组机制，迄今仍未被阐明。本研究报道了一项历时超30年的进化实验，旨在检验两种具有不同性染色体系统的剑尾鱼属（Xiphophorus）鱼类之间的杂交与选择所产生的基因组效应。研究发现，基因渐渗（introgression）与针对色素沉着表型（pigmentation phenotypes）的选择作用，会使意外庞大的母源基因组区域得以保留。在杂交过程中，一个亲本物种的X染色体性别决定区域易位至杂交后代的常染色体（autosome）上，进而演化出全新的性染色体。本研究结果凸显了杂交基因组观测模式背后影响因素的复杂性，并通过实验证实了杂交（原文此处内容未完整）。