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

Abstract

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 pollinators, analysed flower colour perception and tested for differences in pollinator visitation. We also experimentally analysed pollinator limitation in fruit and seed set, and the degree of autonomous selfing. The incidence of florivory and leaf herbivory was compared over 3-4years. Silene littorea is mainly pollinated by bees and butterflies. Pollinators preferred pink flowers, which did not show pollinator limitation. On the contrary, white flowers showed pollinator limitation in fruit set. White-flowered plants had less floral display and higher levels of florivory than pink plants. Flower colour morphs of S. littorea can reproduce in the 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, respectively. 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 more frequently visit pink flowers, which is reflected in pollinator limitation of fruit set in white flowers. Moreover, this species has a mixed mating system in which both colour morphs can reproduce in the absence of pollinators by autonomous selfing, although white flowers mainly produce fruits by autogamy. We suggest that reproductive assurance by autonomous selfing helps to maintain flower colour polymorphism in this population.