Kwok, Allison

Diversity of flowers in flowering plants is understood to facilitate mating success, and yet understanding the relationships between plant sexual diversity and mating patterns remains a challenge. In this thesis, I used Sagittaria latifolia, an aquatic plant with unique sexual systems, to investigate relationships between plant sexual diversity, mating patterns, and reproductive success and to understand their evolutionary consequences. First, I measured the magnitude of sexual selection in a dioecious and a monoecious population of S. latifolia, while accounting for size variation. I showed that sexual selection does operate in natural populations of plants. Estimates of sexual selection were similar in both populations, possibly due to the temporal separation of female and male flowering in hermaphroditic S. latifolia, enabling individuals to act temporarily as unisexuals. Second, I examined how seasonal differences in sex allocation and flowering time can affect male mating opportunities, and the effect on reproductive success in hermaphroditic S. latifolia. I found that shifting allocations to be more male-biased with earlier flowering increased male mating opportunities. However, greater mating opportunities did not equate to higher rates of siring, indicating that factors other than temporal overlap contribute to male reproductive success. Finally, I determined the factors affecting mating and reproductive success of males and male-function hermaphrodites, distinguishing between the predictable effects of plant-level traits and population-level features, and unpredictable effects of stochastic factors. Across both populations, we found that plant-level traits had a greater impact on mating and reproductive success than population-level features. Nevertheless, these effects were frequently masked by stochastic factors. Furthermore, unexplained variation in mating and reproductive success may stem from additional plant traits affecting post-pollination gametophyte-sporophyte interactions. My findings indicate that while sexual selection does operate in natural populations of S. latifolia as expected under Bateman's principles, temporal overlap in flowering, plant traits and population features did not explain patterns of male mating or reproductive success, suggesting that post-pollination factors may be influencing mating outcomes.

Author Keywords: Phenology, Plant mating, Plant reproduction, Sagittaria latifolia, Sex allocation, Sexual selection