Sex Change and Life History Pattern in the Shrimpthor Manningi(decapoda: Caridea): A Novel Case of Partial Protandric Hermaphroditism

A population of Thor manningi sampled for one year was composed of 50% primary males, 49% protandric hermaphrodites, and 1% primary females. Primary males have prehensile third pereiopods, massive appendices masculinae, and life-long sperm production. Protandric hermaphrodites pass first through a male phase (non-prehensile third pereiopods, small appendices masculinae, sperm production) and a transitional phase (reduction of appendices masculinae and sperm ducts, development of female incubatory flanges, ovarian development) before maturing into breeding (embryocarrying) females. Eighty-six to 100% of females (female-phase hermaphrodites and primary females) in monthly samples carried embryos. Breeding females produced new embryo clutches approximately every nine days. Although reproduction was continuous, recruitment chiefly occurred in the summer. Measurements of density, size-specific dry weight, and cohort analysis indicate average life spans of approximately 4-5 months, production of 35 mg dry weight/m2/year, and a production:biomass ratio of 4.5. Primary males do not occur in other protandric decapod species. It is hypothesized that T. manningi primary males persist at a high frequency in the population because they may be more efficient at fertilizing breeding females than are male-phase hermaphrodites.