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 add ition, female spermathecal contents were genotyped at the two loci and histological analysis of the organs was carried out to elucidate patt erns of sperm competition. Females carrying their first brood from con trolled 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 in dicated that the last mate to inseminate a female before oviposition g ained paternity of the clutch. The predominant mechanism ensuring sing le paternity appeared Co be sperm stratification. In wild-caught femal es, the microsatellite typing of the offspring also revealed single pa ternity, but larvae appeared to be sired bq; males whose genotypes wer e found in the spermathecal cross sections towards the dorsal end (bli nd end) of the spermathecae. This suggested that they were the first m ales to mate with females that they guarded until oviposition, and fem ales remated with other males thereafter.