A molecular dissection of the mating system of the Dungeness crab, Cancer magister (Brachyura: Cancridae), with observations on mating behavior

This dissertation presents several new insights into the reproductive biology of the Dungeness crab, Cancer magister. The research is divided into two main components: genotyping of embryos and sperm using microsatellites and behavioral observations of mating pairs of crabs. The isolation, PCR amplification, and descriptive statistics of six microsatellite loci are described for C. magister. All six loci conformed to expectations under Mendelian inheritance and showed no evidence of linkage. Three loci were used to determine paternity of crab embryos produced through controlled laboratory matings. Additionally, the spermathecal and bursal sperm stored by the females from these matings was genotyped to elucidate patterns of sperm storage and use. Spermathecal and bursal sperm and egg clutches from female crabs of unknown mating history were similarly analyzed. Genotyping of eggs revealed that bursal sperm were not used in fertilization. Multiple paternity was found in clutches from controlled matings and 40% of the clutches carried by crabs of unknown mating history. Males achieved last male sperm precedence through ejaculate stratification within the spermatheca; however, stratification may fail when large volumes of stored sperm are present in the spermatheca resulting in multiple paternity. Sperm competition is interannual between the single primary male mate at each molt (adult females molt and mate annually and sperm is retained across molts). Despite possessing internal sperm storage organs where oocytes first encounter sperm, fertilization may occur externally. Detailed observations of mating behavior of pairs of C. magister, as well as observations between crabs during male-male contests for pre-molt females were conducted. Data on the timing of reproductive events from study sites in Puget Sound, Washington is presented. Adult female molting occurred in April to June peaking in April; females molting to maturity (pre-molt carapace width 90.0-99.9 mm) in October and November also mated. Mating marks (made during mating activities) on male chelipeds were not reliable indicators of successful mating. The pre-copula period extended up to 18 days (mean 2.7 days); the post-copulatory guarding period was two to three days. Male crabs have longer 1st walking legs than similarly-sized females and use them for stability during copulation.