The effects of pollination, herbivory and autonomous selfing on the maintenance of flower colour variation inSilenelittorea

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 3–4 years. 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.

Indirect Selection on Flower Color in Silene littorea

“…However, in Barra, the higher flower production was found in plants with darker flowers that consequently produced more seeds. Previous studies had found autonomous selfing in S. littorea, although pollinator visitation was required to reach full seed-set (Casimiro-Soriguer et al, 2015;Buide et al, 2020). In Barra population, Buide et al (2020) reported that pollinators preferably visited pink flowers, and white-flowered plants under free pollination reached fruit-set values similar to those obtained by autonomous selfing.…”

“…Previous studies had found autonomous selfing in S. littorea, although pollinator visitation was required to reach full seed-set (Casimiro-Soriguer et al, 2015;Buide et al, 2020). In Barra population, Buide et al (2020) reported that pollinators preferably visited pink flowers, and white-flowered plants under free pollination reached fruit-set values similar to those obtained by autonomous selfing. Thus, the lower male and female fitness of white-flowered plants in Barra could be related to their lower pollinator attraction, but the lower fitness seems mainly due to their lower flower production.…”

“…Hermaphrodite flowers are protandrous with 10 stamens that open sequentially mostly before the receptivity of the stigma, but some overlaps between sexual phases exist (Casimiro-Soriguer et al, 2013). Silene littorea is a self-compatible species, with incomplete protandry that allows some levels of autonomous selfing (Casimiro-Soriguer et al, 2015;Buide et al, 2020).…”

“…), flower color shows a genetically determined continuous variation from dark pink to white, which so far has been analyzed considering the dark pink, light pink, and white categories for simplicity, with frequency distribution of colors differing drastically among populations (Casimiro-Soriguer et al, 2016;Del Valle et al, 2019). Although S. littorea is self-compatible, it needs pollinator visitation to achieve complete seed production per fruit (Casimiro-Soriguer et al, 2015;Buide et al, 2020), and pollinators can thus be agents of phenotypic selection on flower color. Bees and butterflies were the main pollinators of S. littorea and they preferentially visited pink vs. white flowers (Buide et al, 2020).…”

“…Although S. littorea is self-compatible, it needs pollinator visitation to achieve complete seed production per fruit (Casimiro-Soriguer et al, 2015;Buide et al, 2020), and pollinators can thus be agents of phenotypic selection on flower color. Bees and butterflies were the main pollinators of S. littorea and they preferentially visited pink vs. white flowers (Buide et al, 2020). Since some pollinators, such as bees, can differentiate among flowers that differ subtly in color (Garcia et al, 2017), it is worth considering the whole variation from pink to white and the effect of such color variation on fitness.…”