Evolution of flowering time due to variation in the onset of pollen dispersal among individuals

The evolution of flowering time is often attributed to variation of pollinator rates over time. This study proposes that flowering time can evolve through siring success variation among individuals caused by differential pollen dispersal timing (a result of flowering time variation itself). Quantitative genetic models show that earlier flowering evolves under low pollen removal rates, high pollen deposition rates, and a slow decline in the fertilization ability of removed pollen. Variations in pollen dispersal timing also select for a stable variance in flowering time, which is larger when pollen removal rates are either very low or high, pollen deposition rates are moderate, and the fertilization ability of removed pollen declines more rapidly. Also, a model on the coevolution of flower longevity and flowering time predicts that under constant pollination rates, non-random mating results in a weak correlation between late flowering and longer-lived flowers. This baseline finding suggests that the observed correlation between late flowering and shorter flowering duration in nature is influenced by other factors, such as declining pollination rates during late-stage flowering. I discuss the role of altered pollination rates under climate change during flowering time evolution and the importance of distinguishing between pollen removal and deposition rates.