Population variation and sexual dimorphism in the deep-sea crab Parilia alcocki (Brachyura, Leucosiidae)

Parilia alcocki is a deep-sea crab inhabiting the continental shelves and slopes of the eastern Arabian Sea and western Bay of Bengal at a depth of 128–457 m. No published information is available on its population characteristics and sexual dimorphism. The present study provides the first-ever insight into the population differentiation and sexual dimorphism in P. alcocki using Geometric Morphometric Analysis (GMA) of carapace and chela shapes. The Arabian Sea population possessed carapaces with a more pointed anterior and a rounded posterior margin as compared with the Bay of Bengal population. When chela shapes are compared, the Arabian Sea crabs possess an elongated, narrower arm, and shorter pollex. The observed shape variations could be attributed to heterogeneous habitat conditions in these regions which influence feeding and predation. Sexual dimorphism in carapace shapes was indiscernible. However, males exhibited wider intra-specific variations in carapace shape and show a larger average and maximum size for linear carapace measurements. Also, male crabs possess elongated and narrow arms and shorter pollex, whereas the females have a broader and shorter arm and longer pollex, indicative of classical sexual size dimorphism. Our study confirmed the suitability of GMA to understand the ecological and biological characteristics and trait-habitat linkages of P. alcocki.阿尔科克帕里亚蟹（Parilia alcocki）是一种栖息于阿拉伯海东缘及孟加拉湾西部大陆架与大陆坡海域的深海蟹类，其栖息水深范围为128~457米。目前尚无关于该物种种群特征与性别二态性的公开研究报道。本研究通过对头胸甲与螯足形态开展几何形态测量学分析（GMA），首次解析了阿尔科克帕里亚蟹（P. alcocki）的种群分化与性别二态性。与孟加拉湾种群相比，阿拉伯海种群的头胸甲前缘更为尖锐，后缘更显圆润。在螯足形态上，阿拉伯海种群的蟹类腕节更为细长狭窄，指节更短。观测到的形态差异可归因于两地异质性的栖息环境条件，此类环境条件会影响蟹类的摄食与捕食行为。头胸甲形态的性别二态性并不显著。然而，雄性个体的头胸甲形态种内变异程度更高，其头胸甲线性测量值的平均与最大尺寸均更大。此外，雄性蟹类的腕节细长狭窄、指节较短，而雌性个体的腕节更宽短、指节更长，这符合典型的性别大小二态性特征。本研究证实，几何形态测量学分析（GMA）可用于解析阿尔科克帕里亚蟹的生态与生物学特征，以及性状与栖息环境之间的关联。