Life History Constraints Facilitate the Evolution of Androdioecy and Male Dwarfing

Abstract

“Sex allocation” is the allocation of resources between male and female functions, while “life history strategy” is one between growth and reproduction (and survival). Although life history strategy and sex allocation theories have commonly been studied separately, they interact strongly since both study the optimal allocation of resources available for each individual. For example, individuals with different life history schedules may also differ in terms of sexuality. To illustrate how such life history/sex allocation polymorphism evolves to form various sexual systems such as androdioecy (the coexistence of males and hermaphrodites), I introduce simple mathematical models that consider how constraints (temporal or spatial limitations) on the decision-making of life history path facilitate the coexistence of individuals with different schedules of resource allocation (life history and sexuality), focusing on androdioecious barnacles (dwarf males + hermaphrodites) as an example. The temporal limitation model shows that an unlucky individual who enters an old microhabitat should become a dwarf male to make the best of a bad situation. Although the individual’s fitness could be higher if it has sufficient time for growth in a young microhabitat, becoming a dwarf male is the optimal tactic for the unlucky individual. The coexistence of different sexualities was also explained by the spatial limitation model, which assumes life history constraints among based on the microscopic environmental conditions.