Asexual Reproduction as Part of the Life Cycle in Sacculina Polygenea (Cirripedia: Rhizocephala: Sacculinidae)

Abstract

Sacculina polygenea is a parasite of the intertidal crab Hemigrapsus sanguineus in Kyushu, Japan. Populations from 2 localities differing widely in prevalence (1.1-1.7% and 41.6-79.6%) were compared. When the parasite externae perish, they are replaced by new ones in almost every crab observed irrespective of locality. The abdomen of 29 parasitized crabs from both localities contained numerous internal tumors (primordial parasites). Their number varied between 10 and 92 per crab in the low-prevalence locality and 20 and 71 in the high-prevalence locality. We conclude that the tumors (and externae) of each crab arise by asexual reproduction through budding from the root system of the parasite. The parasites generally become external in crabs 1.5-2 years old. We estimate that the externae die and are replaced 1-3 times during the life of a crab, the host molting and growing between replacements. Concomitantly, the average number and size of the externae increase at each instar. Sacculina polygenea offers the first proven case of asexual reproduction in the family Sacculinidae.