Life history and sexual system of barnacles: a theoretical perspective

Barnacles show one of the most diverse sexual systems in animals: hermaphroditism, dioecy (males and females), and androdioecy (males and hermaphrodites). In addition, when present, male barnacles are very small and are called ‘‘dwarf males’’. I review the theoretical studies on barnacles’ sexual systems in the context of sex allocation and life history theories. I first introduce the sex allocation models by Charnov, especially in relation to the mating group size, and a new expansion model of the evolution of androdioecy is also proposed. My theoretical studies showed that limited mating opportunity favors androdioecy and dioecy over hermaphroditism. In addition, other factors, such as rates of survival and availability of food, are also important. I discuss the importance of empirical studies testing these predictions and how empirical studies interact with theoretical constructs.