Multiple choice criteria and the dynamics of assortative mating during thefirst breeding season of female snow crab Chionoecetes opilio (Brachyura, Majidae)

Crab pairs, consisting of a male grasping another crab (the graspee), were collected by divers during the first breeding season of female snow crab Ch ionoecetes opilio. Different types of graspees were found and were ranked a ccording to their reproductive value to the male. High-value graspees were pubescent females (close to their terminal maturity molt) and nulliparous f emales (just molted and close to oviposition). Postmolt primiparous females (clean-soft shell and carrying eggs) also mated and were inseminated by ma les, but they were of less value than pubescent or nulliparous females as t here was only a remote chance that the males' stored sperm would be used to fertilize the next egg clutch. Females copulated with up to 6 different ma les during their first breeding season. Another category of graspees includ ing males and juvenile females provided the grasping male with no fecundity benefit. Pubescent females paired with males up to 13 d before molting. Ma les grasping the high-value pubescent and nulliparous females were larger, had a harder shell, and were missing fewer Limbs than the males grasping lo w-value primiparous females, other males or juvenile females and than the o verall population of adult males on the mating grounds assessed by trawl. S ize-assortative mating by male chela size and female carapace width occurre d in the predominant pubescent pairs. Moreover, males with larger chelae we re associated with pubescent females missing fewer limbs or having relative ly narrower abdomens. Both traits may influence female survivorship and lif etime fecundity. The complex assortative mating pattern of snow crabs appar ently derives from mate choice and male sexual competition in the context o f prolonged attractiveness of pubescent females to males.