Structure of the Female Reproductive Tract in the Dungeness Crab (Cancer magister) and Implications for the Mating System.

Abstract

Anatomical and behavioral aspects of reproduction in female Dungeness crab, Cancer magister, were investigated. Female crabs were collected over a two-year period and external indicators of reproductive condition were recorded. A subset of crabs was retained for macroscopic and histological examination of the reproductive tract. In addition, males and females were held in the laboratory for mating observations, thus providing females of known mating history for dissection. The spermatheca is of the "ventral type," i.e., the vagina and the oviduct open into the spermatheca in close proximity to each other. A novel organ that often contains sperm, the bursa, is separate and distinct from the spermatheca in both position and origin and is reported for the first time for a brachyuran crab. The bursa is located just inside the vulva, distal to the spermatheca, and opens into the vagina. The sperm plug of C. magister, described here for the first time, is unique in form among cancrids. The sperm plug is placed in the vagina by the first male to mate with a soft-shelled female and prevents subsequent access to the spermatheca. However, the sperm plug does not occlude the vulva nor prevent subsequent copulation; ejaculates from subsequent matings are deposited in the bursa. Hypotheses of the possible function of the bursa are discussed.