A test of hypotheses on male mating systems and female molting in decapod shrimp, using Sicyonia dorsalis (Decapoda: Penaeoidea)

It has been hypothesized that male defense of females should evolve in crustacean species in which females molt prior to mating. Mate guarding of premolt females has been demonstrated in decapods in which males have traits such as equal or larger size than females, well-developed chelipeds, and notably aggressive behavior. However, there are numerous species in the shrimp taxa Penaeoidea and Caridea in which males are smaller than females and ''weakly armed'' with relatively small chelipeds. Precopulatory mate guarding has not been described in these species. The hypothesis of male recognition and guarding of premolt females was tested in Sicyonia dorsalis using video observations on mixed groups of males, intermolt females, and premolt females. Males did not associate with nor defend premolt females, but instead occasionally contacted all females using a courtship behavior (''following''). Courtship and copulations increased dramatically after a female molted. There was no aggressive behavior nor direct physical competition among males for such receptive females. In another set of observations, individual females were kept in isolation for up to 3 weeks after molting before presentation to males. Males were attracted to and mated with these females with empty seminal receptacles, indicating that female receptivity, not tactile and chemical stimuli associated with female molting, are most important in sex attraction in this species. A male tactic of searching for and briefly testing females for copulatory condition, rather than prolonged defense of a single premolt female, may be common in shrimp species with small, weakly armed males.