The evolution of males: support for predictions from sex allocation theory using mating arrays of Sagittaria latifolia (Alismataceae)

Investment in male function should often yield diminishing fitness returns, subjecting the evolution of male phenotypes to substantial constraints. In plants, the subdivision of male function via the gradual presentation of pollen might minimize these constraints by preventing the saturation of receptive stigmas. Here we report on an investigation of (a) patterns of investment in male function by plants in hermaphroditic (monoecious) and dioecious populations of Sagittaria latifolia, and (b) patterns of siring success by males vs. hermaphrodites in experimental mating arrays. We show that in natural populations, males from dioecious populations had greater investment in male function than hermaphrodites in monoecious populations. However, as a proportion of total flower production, males presented substantially fewer flowers at once than hermaphrodites. In comparison with hermaphrodites, therefore, males prolonged the period over which they presented pollen. In mating arrays comprised o...