In order to uncover the sexual difference in morphology and how early they appear during the development stage of mud crab Scylla paramamosain, we measured, observed, and biostatistically analyzed morphological traits related to sex. For unveiling the morphological differences between sexes, morphological traits involving abdomen width (AW), carapace length (CL), and carapace width (CW), were first measured during the crablet development stage of the S. paramamosain in the present study. The correlation analyses and path analyses exhibited that sexual dimorphism in third abdomen width (AW3) and fourth abdomen width (AW4) could be used for sex identification from stage C Ⅵ (stage Ⅵ of crablet). Based on the stepwise discriminant analysis and standardized traits, a sex discriminant equation was constructed, which is capable for sex identification in crablets from stage C Ⅵ. Observations for secondary sexual traits and abdomen morphology (shape and pleopods) using a dissecting microscope or scanning electron microscope indicated that sexes are easily identified at stage C Ⅷ according to the abdomen shape, meanwhile, at stage C Ⅱ based on pleopods difference, and at stage C Ⅰ by the presence or absence of gonopores. The findings in this study contribute greatly to the accuracy of sex identification of the S. paramamosain during the early development stage, which promotes the understanding of the morphological differentiation mechanism of sex.

中文翻译：

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泥蟹Scylla paramamosain发育早期基于形态特征的性别分化证据

为了揭示泥蟹 Scylla paramamosain 发育阶段的性别差异及其出现的时间，我们对与性别相关的形态特征进行了测量、观察和生物统计分析。为了揭示两性之间的形态差异，本研究首先在 S. paramamosain 的小蟹发育阶段测量了涉及腹部宽度 (AW)、背甲长度 (CL) 和背甲宽度 (CW) 的形态特征。相关分析和路径分析表明，第三腹宽（AW3）和第四腹宽（AW4）的性别二态性可用于CⅥ期（小蟹Ⅵ期）的性别识别。基于逐步判别分析和标准化特征，构建性别判别方程，能够对CⅥ期的小蟹进行性别鉴定。用解剖显微镜或扫描电子显微镜观察第二性征和腹部形态（形状和腹足）表明，CⅧ期根据腹部形状容易识别性别，同时，CⅡ期根据腹足差异，在C Ⅰ期由生殖孔的存在与否决定。本研究结果对提高拟南芥在早期发育阶段性别鉴定的准确性有很大帮助，促进了对性别形态分化机制的理解。用解剖显微镜或扫描电子显微镜观察第二性征和腹部形态（形状和腹足）表明，CⅧ期根据腹部形状容易识别性别，同时，CⅡ期根据腹足差异，在C Ⅰ期由生殖孔的存在与否决定。本研究结果对提高拟南芥在早期发育阶段性别鉴定的准确性有很大帮助，促进了对性别形态分化机制的理解。用解剖显微镜或扫描电子显微镜观察第二性征和腹部形态（形状和腹足）表明，CⅧ期根据腹部形状容易识别性别，同时，CⅡ期根据腹足差异，在C Ⅰ期由生殖孔的存在或不存在决定。本研究结果对提高拟南芥在早期发育阶段性别鉴定的准确性有很大帮助，促进了对性别形态分化机制的理解。