Partial Masculinization of Female Eriocheir japonicus (Brachyura, Grapsidae) by Androgenic Gland Implantation

Abstract

Androgenic gland (AG) implantation was carried out on the female young crab, Eriocheir japonicas, at the third instar. Out of the 60 AG-implanted females, 23 individuals were found to be partially masculinized. Moreover, no significant differences were detected in survival rate, carapace width and intermolt periods between normal females and muscle-implanted or AG-implanted females. These results imply that the implantation technique employed in this study does not cause any great harm to the survival and growth of young crabs of E. japonicas, and is effective in the induction of masculinization of the female.
In all of the masculinized females, the degeneration of the third to fifth pleopods, change of the second pleopods to second gonopods and appearance of the first gonopods (i. e., first pleopods) were observed. This result shows that the AG in E. japonicas has the function of masculinization. Based on the light microscopic observations of the internal organs, however, the AG-implanted females still maintained female genital ducts and had no trace of male genital ducts.
The length-frequency distribution of the first gonopods of the masculinized females was much greater than that of normal males. Two masculinized females were found to have giant first gonopods. The degree of morphological completion of these giant first gonopods is much higher than that of the normal male. These are considered to be the products in the reaction of the pleopods to an excess of AG hormone. Therefore, it is suggested that a high upper limit exists in the sensitivity of the pleopods of E. japonicas to AG hormone.