Sperm competition and paternity assurance during the first breeding period of female snow crab (Chionoecetes opilio) (Brachyura: Majidae)

Two highly polymorphic microsatellite DNA loci were used to determine paternity of larvae of primiparous Chionoecetes opilio females. In addition, female spermathecal contents were genotyped at the two loci and histological analysis of the organs was carried out to elucidate patterns of sperm competition. Females carrying their first brood from controlled laboratory matings and from matings in the wild were examined. Spermathecal contents from wild-caught females were cut into several cross sections and each section genotyped individually. Both wild and laboratory females commonly mated with several males whose ejaculates were stored and stratified in the spermathecae. Genetic typing of the offspring of laboratory-mated females revealed single paternity and indicated that the last mate to inseminate a female before oviposition gained paternity of the clutch. The predominant mechanism ensuring single paternity appeared Co be sperm stratification. In wild-caught females, the microsatellite typing of the offspring also revealed single paternity, but larvae appeared to be sired bq; males whose genotypes were found in the spermathecal cross sections towards the dorsal end (blind end) of the spermathecae. This suggested that they were the first males to mate with females that they guarded until oviposition, and females remated with other males thereafter.