Sexual reproduction is a ubiquitous basic feature of life and genetic sex determination is thus widespread, at least among eukaryotes. Understanding the remarkable diversity of sex determination mechanisms, however, is limited by the paucity of empirical studies. Here, we traced back the evolution of sex determination in an entire clade of vertebrates and uncovered that the northern pike (Esox lucius) master sex-determining gene initiated from a 65 to 90 million-year-old gene duplication and remained sex-linked on undifferentiated sex chromosomes for at least 56 million years. Contrasting with its ancient origin, we identified several independent species- or population-specific transitions of sex determination mechanisms in this lineage, including an unexpected complete and recent Y-chromosome loss in some North American northern pike populations. These findings highlight the diversity of the evolutionary fates of master sex-determining genes and raise the importance of careful considerations of population demographic history in sex determination studies. Our study also puts forward the hypothesis that occasional sex reversals and genetic bottlenecks provide a non-adaptive explanation for sex determination transitions.

中文翻译：

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古代北方派克大师性别决定基因的兴衰

有性生殖是生活无处不在的基本特征，因此遗传性别决定至少在真核生物中广泛存在。然而，由于缺乏经验研究，对性别决定机制的显着多样性的了解受到限制。在这里，我们追溯了整个脊椎动物进化支中性别决定的进化过程，发现北部派克（Esox lucius）的主要性别决定基因起始于65到9000万年前的基因复制，并一直保持着性别联系。至少5600万年未分化的性染色体。与它的古老起源相反，我们在该谱系中确定了几个独立的物种决定或特定群体的性别决定机制的转变，包括一些北美北部派克种群中意外的完整和最近的Y染色体丧失。这些发现突出了主要性别决定基因进化命运的多样性，并提高了在性别决定研究中仔细考虑人口统计历史的重要性。我们的研究还提出了这样的假设，即偶然的性逆转和遗传瓶颈为性别确定的过渡提供了非自适应的解释。