ETHOGRAM OF BEHAVIOR WITH EMPHASIS ON MATING FOR THE TANNER CRAB CHIONOECETES BAIRDI RATHBUN

Abstract

Laboratory observations of mating behavior of the Tanner crab Chionoecetes bairdi are described and compared with similar phenomena in other brachyuran crabs. Twenty-seven distinct actions were performed by C. bairdi during 133 matings. Seven actions-carapace caressing, bouncing, body lifting, palpating, sternum-to-sternum positioning, intromission, and pull-up-were unique to reproduction. Grasping, antennule flicking, sternum-to-sternum positioning, vigorous moving of mouthparts, and intromission were common to every complete copulation. Most primiparous females mated shortly after their maturity molt while in a new, soft-shelled condition. However, other primiparous females mated in a semihard-shelled condition as late as 21 days after the maturity molt and still produced viable zygotes. Multiparous females were able to fertilize eggs with sperm stored in their spermathecae during the preceding breeding season. Breeding recurred when males were present at the time multiparous females were receptive (during and shortly after the hatching of their eggs). Courtship, which is subtly developed, entails precopulatory attendance of the female by the male and performance of actions (body lifting, beating, and kicking) which quiet the female if she attempts to escape. Ungentle male-female interactions were infrequent when the female's exoskeletal condition was new and soft, more frequent when the female had a new semirigid exoskeleton, and prevalent when the female had an old, hard exoskeleton. In consequence, both the ability of the females to thwart breeding attempts by small and/or weak males and the occurrence of grasping marks on female exoskeletons directly increased with exoskeletal hardness. In some instances more than one male copulated with individual females. The brachyuran crab Chionoecetes bairdi Rathbun is widely distributed in the northern North Pacific Ocean between the central