Data from: Highly conserved Z and molecularly diverged W chromosomes in the fish genus Triportheus (Characiformes, Triportheidae)

The main objectives of this study were to test (i) if the W chromosome differentiation matches to species' evolutionary divergence (phylogenetic concordance) and (ii) if sex chromosomes share a common ancestor within a congeneric group. The monophyletic genus Triportheus (Characiformes, Triportheidae) was the model group for this study. All species in this genus so far analyzed have ZW sex chromosome system, where the Z is always the largest chromosome of the karyotype, while the W chromosome is highly variable ranging from almost homomorphic to highly heteromorphic. We applied conventional and molecular cytogenetic approaches including C-banding, rDNA mapping, comparative genomic hybridization (CGH) and cross species whole chromosome painting (WCP) to test our questions. We developed Z and W chromosome paints from T. auritus for cross species WCP and performed CGH in a representative species (T. signatus) to decipher level of homologies and rates of differentiation of W chromosomes. Our study reveled that the ZW sex chromosome system had a common origin, showing highly conserved Z chromosomes and remarkably divergent W chromosomes. Notably, the W chromosomes have evolved to different shapes and sequence contents within ~15-25 MYA of divergence time. Such differentiation highlights a dynamic process of W chromosome evolution within congeneric species of Triportheus.本研究的核心研究目标有二：其一，验证W染色体的分化是否与物种的演化分化（phylogenetic concordance，系统发育一致性）相匹配；其二，验证同属类群内的性染色体是否共享共同祖先。本研究以单系三角鲤属（Triportheus，三角鲤科Triportheidae，脂鲤目Characiformes）作为模型类群。截至目前，该属所有已完成分析的物种均采用ZW型性染色体系统：其中Z染色体始终为核型（karyotype）中最大的染色体，而W染色体则呈现高度多态性，形态从近乎同形（homomorphic）到高度异形（heteromorphic）不等。本研究采用常规与分子细胞遗传学手段，包括C带（C-banding）、核糖体DNA（rDNA）定位（rDNA mapping）、比较基因组杂交（comparative genomic hybridization, CGH）以及跨物种全染色体涂染（cross species whole chromosome painting, WCP），用以验证上述科学问题。我们从亮鳍三角鲤（Triportheus auritus）的Z、W染色体制备涂染探针，用于跨物种WCP实验，并在代表物种饰纹三角鲤（Triportheus signatus）中开展CGH实验，以解析W染色体的同源程度与分化速率。本研究揭示，ZW型性染色体系统具有共同起源，Z染色体高度保守，而W染色体则呈现显著分化。值得注意的是，在约1500万至2500万年（MYA，百万年前）的分化时间尺度内，W染色体已演化出各异的形态与序列组成。此类分化特征清晰展现了三角鲤属同属物种间W染色体演化的动态进程。