Genetic confirmation of “egg parasitism” in androgenetic freshwater Corbicula clams by paternity testing using microsatellite DNA markers

抄録

Corbicula leana and C. fluminea are hermaphroditic and ovoviviparous freshwater clams. Although they are considered to reproduce using self-fertilization, the possibility of outcrossing was suggested due to lineage discordance between mitochondrial and genomic DNA. In these species, outcrossing means “egg parasitism” by the spermatozoa from one or more other clams, because they reproduce by androgenesis in which only the nucleus of spermatozoa is transmitted to the progeny. Moreover, the presence of males in these species was reported in the previous study, and they were estimated to reproduce by egg parasitism of hermaphrodites. In this study, we investigated the paternity of juveniles in the brood pouches of six hermaphrodites by comparing the genotypes of the brooded juveniles, brooding clams, and neighboring adult clams using two microsatellite DNA markers. Brooded juveniles showed either identical genotypes to the parental clam or different genotypes from their parent in one clam with brooding. The genotypes of brooded juveniles were identical to those of neighboring hermaphrodites and males. These results indicate that androgenetic Corbicula reproduce not only by self-fertilization but also by egg parasitism, with outcrossing among hermaphrodites and from males to hermaphrodites.