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Abstract
Androdioecy was first described by Darwin in his seminal work on barnacle diversity; he was the first to identify dwarfed males and large hermaphrodites in the same reproductive population. Despite Darwin's evidence for androdioecy, it was declared absent from nature in the 1980s, only to later be rediscovered in phylogenetically diverse taxa. Today we realize that androdioecious systems of many plants and animals share astonishing similarities, particularly with regard to their evolutionary history and mating system. Barnacles, however, persist as an oddball with a seemingly different evolutionary trajectory. The present dissertation aimed to clarify the evolutionary dynamics of the androdioecious barnacle Chelonibia testudinaria (Linneaus, 1758). Combining field assays, laboratory trials and genetic parentage assignment studies, I characterized its mating system and life history. I compare those findings to theoretical expectations and other, non-androdioecious systems, and show that males do not have a relative mating advantage, as expected by mating system theory, but that life history is sufficient to maintain androdioecy. Specifically, high mortality rates and early maturation of males maintains androdioecy in this system.