The effects of pollination, herbivory and autonomous selfing on the maintenance of flower colour variation in Silene littorea

Intraspecific flower colour-variation has been generally proposed to evolve as a result of selection driven by biotic or abiotic agents. In a polymorphic population of Silene littorea with pink and white-flowered plants, we studied the diurnal and nocturnal pollinators, analysed flower colour perception and tested for differences in pollinator visitation in plants with pink and white flowers. We also experimentally analysed pollinator limitation in fruit and seed set, and the degree of autonomous selfing in both colour morphs. The incidence of florivory and leaf herbivory was compared over 3-4 years. S. littorea is mainly pollinated by bees and butterflies (61.5 and 36.5 % of total flower visits, respectively). Pollinators may differentiate pink and white, preferring pink flowers, which did not show pollinator limitation. On the contrary, white flowers showed pollinator limitation in fruit set. White-flowered plants had lower floral display and higher levels of florivory than pink plants. Flower colour morphs of S. littorea may reproduce in absence of pollinators by autonomous selfing, setting 20 % and 12 % of fruit and seeds in the pink morph and 27 % and 20 % in the white morph. Fruit set of white flowers produced by autonomous selfing did not differ from open pollinated flowers. In conclusion, S. littorea is pollinated by insects of different orders, that visit more frequently pink flowers, which is reflected in pollinator limitation in fruit set in white flowers. Moreover, it shows a mixed mating system in which both colour morphs may reproduce in the absence of pollinators by autonomous selfing, although white flowers produce fruits mainly by autogamy. We suggest that reproductive assurance by autonomous selfing helps to maintain flower colour polymorphism in this population.