Evolution of sex determination and sexually dimorphic larval sizes in parasitic barnacles.

Among parasitic (rhizocephalan) barnacles, some species have sexually dimorphic larval size and their sex is determined genetically (genetic sex determination, or GSD). In contrast, other species have monomorphic larvae that choose to become a male or a female depending on the condition of the host (environmental sex determination, ESD). We here analyze how the evolution of sex determination and that of sexual dimorphism of the larvae are coupled.
In those species whose females have a few receptacles for dwarf male(s), male larvae engage in an intense interference competition among themselves for the reproductive opportunity, the optimal male larval size is greater than the optimal female larval size, and the genetic sex determination (GSD) should evolve. In contrast, in those species whose females accept many dwarf males simultaneously and replace them at each reproductive event, competition among male larvae is of scramble type, and monomorphic larvae with environmental sex determination (ESD) is likely to evolve.
The work was done in collaboration with JT Hoeg and S Yamaguchi