Multiple pollinator visits to Mimulus ringens (Phrymaceae) flowers increase mate number and seed set within fruits

The timing and effectiveness of pollinator visitation to flowers is an important factor influencing mating patterns and reproductive success. Multiple pollinator probes to a flower may increase both the quantity and genetic diversity of progeny, especially if single probes deposit insufficient pollen for maximal seed set or if the interval between probes is brief. When pollen carryover is limited, sequential pollen loads may also differ markedly in sire representation. We hypothesized that these conditions help explain high levels of multiple paternity in Mimulus ringens fruits. We documented all bee visits to individual flowers, quantified resulting seed set, and determined paternity for 20 seeds per fruit. Most (76%) flowers received multiple probes, and the interval between probes was usually <30 min. Flowers probed multiple times produced 44% more seeds than flowers probed once. All fruits were multiply sired. Flowers receiving a single probe averaged 3.12 outcross sires per fruit, indicating that single probes deposit pollen from several donors. Multiple paternity was even greater after three or more probes (4.92 outcross sires), demonstrating that sequential visits bring pollen from donors not represented in the initial probe.