Diffuse and pairwise natural selection on floral traits of Lobelia siphilitica

Recent research has demonstrated that plant defense traits evolve in response to diffuse selection by multiple herbivores. Floral traits of plants that both require pollinators for reproduction and are attacked by herbivores may also experience diffuse selection. Using a fully factorial manipulative field study of an artificial population, I demonstrated that floral traits of the wildflower Lobelia siphilitica are subject to both diffuse and pairwise selection. I detected diffuse selection on flowering span, inflorescence height, and branch number. I also detected pollinator-mediated pairwise selection on daily display size and flowering span, and herbivore-mediated pairwise selection on daily display size and inflorescence height. As a result, selection on floral traits of Lobelia siphilitica differs depending on the combination of mutualists and antagonists present. If there is evolution in response to such diffuse selection in natural populations, then co-adaptation between L. siphilitica and its pollinator may be constrained in populations experiencing herbivory.