Male Morphotypes and Mating Behavior of the Dancing Shrimp Rhynchocinetes brucei (Decapoda: Caridea)

In crustaceans, the presence of large males with highly developed prehensile appendages (chelipeds or gnathopods) generally is suggestive of female monopolization during her receptive period. While mate guarding is common among some malacostracan crustaceans (brachyuran crabs and some amphipod families) it is relatively rare in caridean shrimp. Here we explored sexual dimorphism and the presence of morphotypic differences among males of the dancing shrimp Rhynchocinetes brucei. We furthermore quantified the behavioral events during mating interactions to examine whether mate guarding extends over the entire period of female receptivity. Males and females had similar body sizes, but males developed increasingly larger third maxillipeds and first chelipeds during ontogeny. Large males with hyperdeveloped maxillipeds and very large chelipeds featured a high degree of broken appendages and eyes, which probably results from intrasexual agonistic interactions. About 30% of the non-competitive male-female interactions with post-ovigerous females resulted in successful matings. Males usually initiated body contact with the female shortly after the female’s parturial molt, and they frequently touched the female’s genital region with their anterior body parts. The first (and in most cases only) spermatophore transfer event occurred at variable times (0.2-7 h) after the female’s molt. Following spermatophore transfer some males guarded the female in the cage state (between their pereiopods) until the female had finished spawning and was ovigerous. Post-copulatory mate guarding could last up to 70 min, but not all males guarded the female after the copulation. We suggest that male guarding of the receptive female throughout the mating process reduces the risk of sperm competition.