Sex-chromosome systems tend to be highly conserved and knowledge about their evolution typically comes from macroevolutionary inference. Rapidly evolving complex sex-chromosome systems represent a rare opportunity to study the mechanisms of sex-chromosome evolution at unprecedented resolution. Three cryptic species of wood-white butterflies—Leptidea juvernica, L. sinapis and L. reali—have each a unique set of multiple sex-chromosomes with 3–4 W and 3–4 Z chromosomes. Using a transcriptome-based microarray for comparative genomic hybridisation (CGH) and a library of bacterial artificial chromosome (BAC) clones, both developed in L. juvernica, we identified Z-linked Leptidea orthologs of Bombyx mori genes and mapped them by fluorescence in situ hybridisation (FISH) with BAC probes on multiple Z chromosomes. In all three species, we determined synteny blocks of autosomal origin and reconstructed the evolution of multiple sex-chromosomes. In addition, we identified W homologues of Z-linked orthologs and characterised their molecular differentiation. Our results suggest that the multiple sex-chromosome system evolved in a common ancestor as a result of dynamic genome reshuffling through repeated rearrangements between the sex chromosomes and autosomes, including translocations, fusions and fissions. Thus, the initial formation of neo-sex chromosomes could not have played a role in reproductive isolation between these Leptidea species. However, the subsequent species-specific fissions of several neo-sex chromosomes could have contributed to their reproductive isolation. Then, significantly increased numbers of Z-linked genes and independent neo-W chromosome degeneration could accelerate the accumulation of genetic incompatibilities between populations and promote their divergence resulting in speciation.

中文翻译：

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Leptidea 木白蝶中与动态基因组改组相关的多条性染色体的进化

性染色体系统往往是高度保守的，关于它们进化的知识通常来自宏观进化推理。快速进化的复杂性染色体系统代表了以前所未有的分辨率研究性染色体进化机制的难得机会。三种神秘的木白蝴蝶——Leptidea juvernica、L. sinapis 和 L. reali——每一种都有一组独特的多条性染色体，带有 3-4 W 和 3-4 Z 染色体。使用基于转录组的微阵列进行比较基因组杂交 (CGH) 和细菌人工染色体 (BAC) 克隆文库，两者都在 L. juvernica 中开发，我们鉴定了家蚕基因的 Z-连锁 Leptidea 直系同源物，并通过荧光原位定位它们与多条 Z 染色体上的 BAC 探针杂交 (FISH)。在所有三个物种中，我们确定了常染色体起源的同线性块并重建了多个性染色体的进化。此外，我们确定了 Z-linked orthologs 的 W 同系物并表征了它们的分子分化。我们的研究结果表明，由于性染色体和常染色体之间的重复重排（包括易位、融合和裂变），动态基因组重组导致多性染色体系统在共同祖先中进化。因此，新性染色体的初始形成不可能在这些 Leptidea 物种之间的生殖隔离中发挥作用。然而，随后几条新性染色体的物种特异性裂变可能导致了它们的生殖隔离。然后，