Adaptive differentiation in floral traits in the presence of high gene flow in scarlet gilia (Ipomopsis aggregata)

Plant-pollinator interactions are thought to be major drivers of floral trait diversity. However, the relative importance of divergent pollinator-mediated selection versus neutral processes in floral character evolution has rarely been explored. We tested for adaptive floral trait evolution by comparing differentiation at neutral genetic loci to differentiation at quantitative floral traits in a putative Ipomopsis aggregata hybrid zone. Typical I. aggregata subsp. candida displays slender white tubular flowers that are typical of flowers pollinated by hawkmoths and subsp. collina displays robust red tubular flowers typical of flowers pollinated by hummingbirds; yet hybrid flower morphs are abundant across the East Slope of the Colorado Rockies. We estimated genetic differentiation (FST) for nuclear and chloroplast microsatellite loci and used a half-sib design to calculate quantitative trait divergence (QST) from collection sites across the morphological hybrid zone. We found little evi...