Pollination, flower size variation and floral symmetry

The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared to actinomorphic flowers. By using data on 43 species from two contrasting communities, Lázaro and Totland show that zygomorphic species that are highly dependent on pollinators and ecologically specialized are less variable in flower size than ecologically generalist and selfing zygomorphic species. However, these relationships are not found in actinomorphic species. The results suggest that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species’ dependence on pollinators.