Chela asymmetry and dimorphism in the red swamp crayfish Procambarus clarkii (Decapoda: Astacidea: Cambaridae)

抄録

The red swamp crayfish Procambarus clarkii exhibits different sexual morphotypes (reproductive type, form I; non-reproductive type, form II) in both sexes after reaching sexual maturity. This crayfish species shows intra- and inter-sexual dimorphisms of chela size: the chelae are largest in the form I males, followed by the form I females and form II males, and are the smallest in the form II females. Chelipeds of this species are asymmetrical, with one chela being larger than the other. However, little is known about the degree of chela asymmetry in P. clarkii. We examined the chela asymmetry and further elucidated the chela dimorphism. Larger chelae occurred randomly on either the right or left sides. The size differences between larger and smaller chelae were primarily small, and some individuals had smaller regenerating chelipeds. Allometric growth analyses revealed the intra- and inter-sexual dimorphisms of chela size and shape, with males and females of form I morphotypes exhibiting slender and wide chelae, respectively. Male P. clarkii’s slender chela may function as useful weapons, whereas female P. clarkii’s large and wide chelae may also function as tools for constructing and maintaining deeper burrows for breeding.