DIOECY, POLLINATION AND SEED DISPERSAL IN AUSTRALIAN SPINY SOLANUM

The causes, consequences and correlates of dioecy have been the subject of much discussion since the days of Darwin. Several more recent authors have stressed the importance of informing the body of theory with studies that focus on lineages in which both dioecy and cosexuality are present. Solanum is an ideal group for this because dioecy, cosexuality and unisexual transitions between them all occur. As a theoretical extension of recent phylogenetic and field-based inquiry, we present three suites of hypotheses regarding the evolution and maintenance of dioecy in Australian spiny Solanum, the group in which much of the dioecy known for the genus (10 of 14 species) occurs. First, we explore the breeding system transitions necessary for dioecy to evolve from andromonoecy. Next, we discuss the potential role of local pollinator behavior in both fostering inbreeding and ensuring outcrossing. Finally, we propose a scenario in which rock-wallabies function as biotic seed dispersal agents of dioecious and andromonoecious Australian solanums through “fecal seed storage” followed by “seasonal redispersal.”