Review of Sexual Selection and Chemical Communication in the Lobster, Homarus americanus

Field and laboratory observations have shown that female lobsters, Homarus americanus, are the active searching partner in courtship, choosing locally dominant males. The attractive features of the male are suspected to be intrasexual aggressive behavior and chemical cues. Size-based dominance is an important factor allowing males to secure a suitable mating shelter. In nature, male and female lobsters often approach and check shelters of other lobsters. This behavior may allow the animals to monitor the observed daily and seasonal changes in their physical and social environment. Premolt females approach the dominant male's shelter frequently in the weeks before the female's molt. Indirect evidence indicates that the female then "blows" a urine-related sex pheromone into the male shelter. One to several days before molting, a female enters the male shelter. Female intrasexual competition increases the premolt, but not the postmolt, cohabitation period. During cohabitation, males fan with their pleopods blowing a strong current through the shelter and into the environment. This chemical advertisement attracts other females, including future mating partners, to his shelter entrance. Females spent 1–2 wk in the male shelter. Mating takes place 30 min after the female molts. Another female may start cohabitation with the male immediately. In one 10-wk period a dominant male in the laboratory cohabited and mated with five females in sequence; females ignored a second male of equal size. Theoretically, by allowing a female to spend time in his shelter the male foregoes other mating opportunities, but this is balanced—and hence a stable strategy—by his protection of a vulnerable postmolt female who carries his offspring. Females must choose males who can protect them efficiently from prédation and, perhaps more importantly, from competing lobsters.