Department of Ecology and Evolution, Biophore, University of Lausanne, 1015, Lausanne, Switzerland.
Swiss Federal Institute of Technology (EPFL), Bâtiment GC, 1015, Lausanne, Switzerland.
Sci Rep. 2017 Nov 3;7(1):15024. doi: 10.1038/s41598-017-14905-9.
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 months after fertilization. We conclude that sex differentiation starts before hatching, goes through an all-male stage for both sexes (which represents a rare case of "undifferentiated" gonochoristic species that usually go through an all-female stage), and is delayed in males. During these juvenile stages males grow faster than females instead of developing their gonads.
鱼类种群可能会受到性分化过程中出现的性别比例失调的威胁。在这里，我们描述了一个遭受性别比例失调的野生灰鳟（Thymallus thymallus）种群的性分化。我们验证了性别决定与鲑鱼的性别决定基因座（sdY）有关。这使我们能够研究性别特异性基因表达和性腺发育。在胚胎发生期间可以观察到性别特异性基因表达，并且在孵化前后非常强烈。大约一半的鱼类在受精后 11 周左右显示出未成熟的睾丸。这种表型在发育过程中主要被“睾丸到卵巢”或“卵巢”表型所取代。其余鱼类的性腺在受精后六个月仍未分化。遗传性别鉴定显示，未分化性腺的鱼类均为雄性，在观察期间比遗传雌性鱼类生长得更大。只有 12%的遗传雄性鱼类在受精后六个月显示出睾丸组织。我们得出结论，性分化在孵化前开始，雌雄两性都经历一个全雄性阶段（这代表了一个罕见的“未分化”的雌雄同体物种，通常经历一个全雌性阶段），并且在雄性中被延迟。在这些幼体阶段，雄性比雌性生长得更快，而不是发育其性腺。
