Sex differentiation in the crab<i>Eriocheir japonicus</i>(Decapoda, Grapsidae)

Abstract

Summary The sex differentiation of the crab Eriocheir japonicus was studied histologically and morphologically from the first zoeal stage to the fifth crab stage. The gonoducts were the first sexual characteristic that underwent sex differentiation. As early as the crab was at the megalopa stage, gender could be determined on the basis of two different orientations of the gonoducts. One orientation was toward the eighth thoracic sternite in the males and the other was toward the sixth thoracic sternite in the females. The second sexual characteristic that underwent sex differentiation was found in the pleopods at the third crab stage. No remarkable morphological or structural difference was observed between the gonia in males and those in females. We compared our findings with those in the crabs studied in previous research regarding the sequences of the sex differentiation of sexual characteristics and the development of gonoducts and gonopores. We also discussed the timing of the appearance of the androgenic gland in the sex differentiation of decapods and other malacostracans. Unlike isopods and amphipods, no androgenic gland is visible prior to sex differentiation in E. japonicus. This finding is consistent with those reported in other decapods. We hypothesize that in decapods, before the androgenic gland cells form a gland, they already exist dispersively in both sexually undifferentiated genetic males and females. In the genetic males, these dispersive androgenic gland cells may be activated by the male sex-determining genes to produce androgenic gland hormones inducing sex differentiation.