Where do monomorphic sexual systems fit in the evolution of dioecy? Insights from the largest family of angiosperms

Abstract

A range of hypothesized evolutionary pathways has been proposed for describing the evolution of dioecy. However, the evolutionary links between other sexual systems not directly involved in dioecy evolution remain largely unexplored, and hence, a comprehensive picture of evolutionary transitions between sexual systems is still lacking. Here, we explored the diversity and evolution of sexual systems in Asteraceae, the largest family of flowering plants, where almost all sexual systems are present. We used a phylogenetic approach to build a model of evolutionary transitions between sexual systems. The best model involved nine transitions, including those from hermaphroditism to andromonoecy, gynomonoecy and gynodioecy, those from gynomonoecy to monoecy and trimonoecy, two transitions to dioecy -one through gynodioecy and the other through monoecy - and reversals from monoecy to gynomonoecy and from gynomonoecy to hermaphroditism. Our reconstruction of the evolution of sexual systems in Asteraceae provided, for the first time, a joint view of the evolutionary transitions between seven sexual systems, unveiling the evolutionary links between monomorphic sexual systems. A pathway from hermaphroditism to monoecy through gynomonoecy, instead of from andromonoecy, was highly supported, which was consistent with a gradient of floral gender specialization. © 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.