Influence of adult male on sexual maturation of male and female larvae in the gnathiid isopod Elaphognathia cornigera

Abstract

Responses of larval individuals of the fish-parasitic gnathiid isopod Elaphognathia cornigera under presence or absence of adult male were examined by a laboratory rearing experiment. Female larvae molted into adults after 29.5±4.8 days (mean±s.d.) under male absence since the final parasitism against 17.4±3.4 days under male presence. Ovulation in females was never observed under male absence during the experimental period while it occurred within a day after maturation of female larvae under male presence. The delayed molting and inhibition of ovulation under male absence are considered to provide additional time for finding a mate when the availability of males is low and to decrease reproductive failure of females. In contrast to females, solitary reared male larvae took less time to mature than those reared with a male. The delayed molting of male larvae under male presence was suggested to contribute to reduce potential attacks from adult males when male-male competition exists. Precopulatory mate guarding behavior by adult males was observed more frequently for female larvae than for male larvae. This indicates that adult males of the gnathiid can discriminate the sex of larvae as well as larvae recognize the presence of males.