THE EFFECT OF PARASITIC CASTRATION BY A CILIATE ON A POPULATION OF ASTERIAS-VULGARIS

Male Asterias vulgaris in Port Daniel Bay, Baie des Chaleurs, Quebec C anada, were found to be infected with the ciliate Orchitophrya stellar um (Cepede). No females were infected. The parasite causes an 85% decr ease in the size of the gonad in infected males, and probably accounts for the low ratio of males to females (0.52) and differences in the s ize distributions of males and females compared to those in an uninfec ted population. The castration of the males almost certainly reduces f ertilization success. (C) 1994 Academic Press, Inc.