Sexual dimorphism in genital papillae of Tripneustes ventricosus

摘要

Sexual dimorphism is rare among echinoids. Where present, it is usually observed in the presence, length, and shape of genital papillae and in the sizes of gonopores. The Tripneustes type of sexual dimorphism (long tubular genital papillae in males, short conical papillae in females) is based on T gratilla, whereas its sole congener, T ventricosus, is reported not to be sexually dimorphic. We found the Tripneustes type to occur in T ventricosus from Florida, with male papillae averaging 906μm and female papillae 460μm in length. Differences in diameters of gonopores of males and females seemed related to differences in test diameter. In addition to existing hypotheses on the adaptiveness of genital papillae and papillar dimorphism, we encourage experimental study of their role in reproductive success of sperm-limited broadcast spawners with viscous semen under differing hydrodynamic conditions. We also urge caution in interpretation of sexual dimorphism of gonopore size without consideration of adult test diameter.