Institute of Hydrobiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China.
Marine Fisheries Research Institute of Zhejiang Province, Zhoushan, China.
Front Endocrinol (Lausanne). 2021 Jan 27;11:542942. doi: 10.3389/fendo.2020.542942. eCollection 2020.
Animal taxa show remarkable variability in sexual reproduction, where separate sexes, or gonochorism, is thought to have evolved from hermaphroditism for most cases. Hermaphroditism accounts for 5% in animals, and sequential hermaphroditism has been found in teleost. In this study, we characterized a novel form of the transient hermaphroditic stage in little yellow croaker () during early gonadal development. The ovary and testis were indistinguishable from 7 to 40 days post-hatching (dph). Morphological and histological examinations revealed an intersex stage of male gonads between 43 and 80 dph, which consist of germ cells, somatic cells, efferent duct, and early primary oocytes (EPOs). These EPOs in testis degenerate completely by 90 dph through apoptosis yet can be rescued by exogenous 17--estradiol. Male germ cells enter the mitotic flourishing stage before meiosis is initiated at 180 dph, and they undergo normal spermatogenesis to produce functional sperms. This transient hermaphroditic stage is male-specific, and the ovary development appears to be normal in females. This developmental pattern is not found in the sister species or any other closely related species. Further examinations of serum hormone levels indicate that the absence of 11-ketotestosterone and elevated levels of 17--estradiol delineate the male intersex gonad stage, providing mechanistic insights on this unique phenomenon. Our research is the first report on male-specific transient hermaphroditism and will advance the current understanding of fish reproductive biology. This unique gonadal development pattern can serve as a useful model for studying the evolutionary relationship between hermaphroditism and gonochorism, as well as teleost sex determination and differentiation strategies.
动物类群在有性生殖方面表现出显著的变异性，其中雌雄异体（gonochorism）被认为是大多数情况下从雌雄同体（hermaphroditism）进化而来的。雌雄同体在动物中占 5%，并且在硬骨鱼中已经发现了连续的雌雄同体。在这项研究中，我们描述了小黄鱼（）在早期性腺发育过程中一种新的短暂雌雄同体阶段的形式。在孵化后 7 到 40 天（dph），卵巢和精巢无法区分。形态学和组织学检查显示，在 43 到 80 dph 之间存在雄性性腺的间性阶段，其由生殖细胞、体细胞、输出管和早期初级卵母细胞（EPOs）组成。这些在睾丸中的 EPOs 通过细胞凋亡在 90 dph 时完全退化，但可以通过外源性 17β-雌二醇挽救。雄性生殖细胞在减数分裂开始前进入有丝分裂旺盛阶段，在 180 dph 时，它们经历正常的精子发生，产生功能性精子。这种短暂的雌雄同体阶段是雄性特有的，而卵巢发育在雌性中似乎是正常的。这种发育模式在姐妹种 或任何其他密切相关的物种中都没有发现。对血清激素水平的进一步检查表明，11-酮睾酮的缺乏和 17β-雌二醇水平的升高划定了雄性间性性腺阶段，为这种独特现象提供了机制上的见解。我们的研究是关于雄性特异性短暂雌雄同体的首次报道，将推进对鱼类生殖生物学的现有理解。这种独特的性腺发育模式可以作为研究雌雄同体和雌雄异体之间的进化关系以及硬骨鱼性别决定和分化策略的有用模型。
