Stevens, Peter (Lawrence University). Mentors: Michele Dudash and Charles Fenster (University of Maryland College Park). The effects of hummingbird mediated selection on combinations of floral color and inflorescence height in Silene virginica (Caryophyllaceae).

Abstract: In recent literature, there has been significant debate regarding the pollination syndromes concept whereby a functional group of pollinators are attracted to and drive selection for various suites of floral traits, including both advertisements and rewards (Faegri and van der Pijl 1979). The findings of recent studies have caused the idea of pollination syndromes and their predictive power to be critically re-examined. This study examined the effects of hummingbird selection for combinations of floral color and inflorescence height in Silene virginica. The first two experiments utilized arrays with combinations of two floral colors (e.g. - red, pink and/or white) and two inflorescence heights (e.g. - tall, short). The third experiment utilized arrays with combinations of all three floral colors and two inflorescence heights. Mean frequency of 1st visitation and total visitation were used to measure hummingbird selective pressure. Data was analyzed using a two-way ANOVA with Type I and III sums of squares and a Tukey's Test. Individually, hummingbirds significantly preferred red floral color to both pink and white and tall inflorescence height over short in almost all cases. In combination, hummingbirds significantly preferred red and tall plants in almost all cases. These results support the efficacy of pollinator syndromes as they confirm selection for and maintenance of floral trait suites considered indicative of the hummingbird pollination syndrome. In addition, they are significant in terms of the evolutionary history of S. virginica, specifically regarding phylogeny and ancestral character states.