Sex differentiation in grayling (Salmonidae) goes through an all-male stage and is delayed in genetic males who instead grow faster

Fish populations can be threatened by distorted sex ratios that arise during sex differentiation. Here we describe sex differentiation in a wild grayling (Thymallus thymallus) population that suffers from distorted sex ratios. We verified that sex determination is linked to the sex determining locus (sdY) of salmonids. This allowed us to study sex-specific gene expression and gonadal development. Sex-specific gene expression could be observed during embryogenesis and was strong around hatching. About half of the fish showed immature testes around eleven weeks after fertilization. This phenotype was mostly replaced by the “testis-to-ovary” or “ovaries” phenotypes during development. The gonads of the remaining fish stayed undifferentiated until six months after fertilization. Genetic sexing revealed that fish with undifferentiated gonads were all males, who grew larger than the genetic females during the observational period. Only 12% of the genetic males showed testicular tissue six mon...

鱼类种群可能因性别分化过程中出现的性别比例失衡而受到威胁。在此，我们描述了一个受性别比例失衡影响的野生茴鱼（Thymallus thymallus）种群的性别分化过程。我们证实，性别决定与鲑科鱼类的性别决定基因座（sdY）相关。这使我们能够研究性别特异性基因表达和性腺发育。性别特异性基因表达在胚胎发生期即可观察到，且在孵化前后表现强烈。受精后约11周，约半数鱼类表现出未成熟的睾丸。发育过程中，这种表型大多被“睾丸向卵巢转化”或“卵巢”表型所替代。其余鱼类的性腺在受精后6个月内保持未分化状态。遗传性别鉴定显示，性腺未分化的鱼类均为雄性，且在观察期内其生长速度快于遗传雌性。仅12%的遗传雄性在6个……时表现出睾丸组织。