The importance of day and night pollinators to the evolution and reproduction of dame's rocket (Hesperis matronalis)

Many plant species are visited by a variety of different pollinator taxa, but the importance of different taxa to plant reproduction and floral evolution is often overlooked. I studied the roles that day and night pollinators of dame's rocket (Hesperis matronalis) play in reproduction and floral evolution. Seed set and natural selection were measured in the presence of day versus night pollinators over two years and in two populations. Day or night pollinators were excluded from inflorescences using mesh bags either removed at dawn and replaced at dusk or removed during dusk and replaced at dawn. Un-bagged inflorescences were used to test for total reproduction in the presence of both day and night pollinators. Selection gradients for floral traits were measured during the day and night using seeds produced from each treatment. Both day and night pollinators effect seed set in dames rocket, but daytime pollinators effect twice as many seeds as nighttime pollinators. Pollinators visiting at night increased total seed production during one year in one population, as inflorescences exposed continually produced more seeds than those exposed only during the day. In one year, selection on anther exsertion differed among day and night pollinators indicating some trade-off in adapting to both groups of pollinators, but individuals with more exserted anthers had high fitness in both treatments. In the following year in one population, both day and night pollinators selected to decrease anther exsertion and increase stamen dimorphism. Both day and night pollinators selected to increase petal area. Although there was evidence for a slight trade-off in adapting to both day and night pollinators, results indicate that dames rocket can be well adapted for both day and night pollinators.