Effects of monkeyflower floral display size on reproductive success through male and female sexual functions
Male and female reproductive success can vary strongly with the number of flowers blooming simultaneously on a plant. Plants with many open flowers often attract more pollinator visits, increasing outcross pollen receipt. However, on large displays pollinators frequently visit several flowers in sequence, which may increase self-pollination and reduce pollen export per flower. To more fully understand how fitness is affected by floral display, we manipulated display phenotypes and then used paternity analysis to quantify siring success and selfing rates.
We established four replicate (cloned) arrays of Mimulus ringens (Allegheny monkeyflower). Each array consisted of genets with unique marker genotypes, allowing unambiguous paternity assignment. Floral displays on plants in each array were trimmed array so that there were equal numbers of plants with two, four, eight and 16 flowers. We scored the number of seeds per ripened fruit, and assigned paternity to 1935 progeny
. Increasing display size sharply reduced siring success per flower, while seed number per flower did not vary with display. Large floral displays experienced an increase in selfing rate, but pollen discounting through geitonogamy reduced siring success much more than the increase in siring through increased selfing
. Total fitness increased with floral display, but the marginal return on each additional flower declined steadily with increases in display size. Fitness could therefore be maximized by producing few-flowered displays over a long flowering period, rather than many-flowered displays over a brief flowering period.