Do pollen and ovule number match the mating environment? An examination of temporal change in a population of Stylidium Armeria

The mating environment hypothesis predicts that during a flowering season, dichogamy can result in temporal variation in the number of pollen donors, selecting for variation in allocation to pollen and ovules in flowers at different positions. However, asynchronous flowering changes the probability of pollen transfer, with later-flowering plants having a higher probability of pollen transfer in their first-produced flowers. We examined the flowering phenology of protandrous Stylidium armeria to determine how flowering asynchrony affects pollen transfer probabilities, female fitness, and allocation to pollen and ovules. While there was a general pattern of increased allocation to male function across the season, early flowers on the earliest plants had the highest pollen/ovule ratio. Stylidium armeria had a small number of early flowering female plants, increasing the probability of pollen transfer from early staminate-phase flowers. Fruit set was significantly influenced by the ratio of staminate/pistillate flowers in the population, and plants flowering earlier than the main population tended to have high female fitness. We suggest that in protandrous populations, the low probability of pollen transfer in early staminate-phase flowers may select for, or maintain, early flowering females.