Courtship and female mate selection in a marine isopod crustacean Paracerceis sculpta

Females are semelparous in Paracerceis sculpta, a harem polygynous isopod that breeds in intertidal sponges in the northern Gulf of California. Reproductive females locate males established in spongocoels, and initiate courtship, which involves oral contact of males by females, and lifting and shaking of females by males. Despite this apparent assessment, females do not discriminate among males that differ by 10% in body length, by 30 days in age, or that lack appendages used in courtship. In most cases, females pair with the first male they encounter. Males, moreover, show no reluctance to pair with any female that approaches their spongocoel. Females as well as males are attracted to spongocoels occupied by multiple gravid females. Males attempt to control such sites, and body size confers an advantage in spongocoel takeover. Predation risks incurred by females while searching for spongocoels may favour individuals responding to chemical cues that reliably indicate breeding site quality, e.g. those emanating from established breeding aggregations. That sponges containing gravid females attract unmated females may explain why males attempt to monopolize these sites.