Sex dimorphism and ontogenetic allometry of Goyazana castelnaui (Crustacea, Brachyura)

ABSTRACT: In crustaceans, studies of dimorphism using geometric morphometry approach are particularly appropriate due to the facility and accuracy in the identification of homologous landmarks. The aim of this study was identify the existence of sexual and age dimorphism of freshwater crab Goyazana castelnaui (H. Milne-Edwards, 1853), except for the dimorphism of the pleon, since it is an aspect intrinsic to the Brachyura. Were determined 10 anatomical landmarks for ventral view and 11 for the dorsal view. A covariance matrix was generated, containing factors related to the sexes and age groups of each sex, and the images were considered symmetrical. The canonical variate analysis (CVA) and discriminant analysis (DA) were performed with 999 permutations and as comparisons were made based on the Hotteling test (T²) of the Procrustes distance. In the ventral view no variation was found in the form of juveniles and adults of females and males (p = 0.4548, p = 0.131, respectively) based on the Procrustres distance. In the dorsal view, a separation was observed between the adult females and the other groups, indicating a noticeable modification of the cephalothorax volume for the allocation of the gonads.

摘要：在甲壳类动物研究中，采用几何形态测量学（geometric morphometry）方法分析形态二态性尤为合适，因其在同源地标点的识别上兼具便捷性与准确性。本研究旨在探究淡水蟹Goyazana castelnaui（H. Milne-Edwards, 1853）的性别与年龄形态二态性，但不包括腹部（pleon）的二态性——因这是短尾下目（Brachyura）物种的固有特征。本研究共设置10个腹面视图解剖地标点与11个背面视图解剖地标点。本研究生成了协方差矩阵，其中包含与各性别及其年龄组相关的因子，并将所有图像视作对称样本。本研究采用999次置换的典范变量分析（canonical variate analysis, CVA）与判别分析（discriminant analysis, DA），并基于普氏距离（Procrustes distance）的霍特林检验（T²）开展组间比较。基于普氏距离分析结果，腹面视图下，雌性与雄性的幼体、成体形态均未发现显著差异（分别对应p=0.4548、p=0.131）。而在背面视图中，成年雌性与其余组别间呈现显著分离，这表明雌性头胸部（cephalothorax）体积发生了明显变化，以容纳生殖腺。