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

ABSTRACT 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.