THOMSON, JD; University of Toronto: Perspectives on the evolution of sexual tactics in animal-pollinated plants: pollen presentation theory and sex allocation theory

Many researchers seeking to understand the great range of sexual expression in flowering plants have referred to sex allocation theory for general conceptual insights. Other approaches are possible. With various colleagues, I have been particularly concerned with the packaging and gradual dispensing of pollen to pollinators. Many plants do this, through morphological and �behavioral� mechanisms that range from obvious to subtle. Simple models, which collectively can be called �pollen presentation theory,� suggest that such patterns can have important effects on fitness achieved through pollen donation. They may thereby influence many aspects of the evolution of sexual modes in plants, including transitions between dioecy and cosexuality. I will review the main implications of the models, discuss recent work from my lab aimed at testing some key predictions, and then contrast pollen presentation theory to sex allocation theory. I hope to speculate on possible applications to hermaphroditic animals.