The level of pollination specialization affects the relationship between the shape of flowers and the bills of their hummingbird pollinators in Antillean Gesneriaceae

Abstract

Premise of research. Pollinators are known to impose strong selection on floral shape. Particularly well studied is the relationship between the flowers of hummingbird-pollinated plant species and the bills of their pollinators. However, no studies to date have evaluated whether these relationships vary according to the level of pollination specialization. Here, we quantify the relationship between the corolla shape of Antillean Gesneriaceae and the bills of their hummingbird pollinators for species with a specialist (one functional group of pollinators: hummingbirds) and a generalist (more than one functional group of pollinators: hummingbirds, bats, and insects) pollination strategy. Methodology. We used phylogenetic generalized least squares analyses on linear measurements and phylogenetic two blocks partial least squares on multivariate geometric morphometrics data to test whether and how the variation in the corolla shape of the Antillean Gesneriaceae is correlated to the shape of the bills of their hummingbird pollinators. Pivotal results. We found that corolla shape is correlated with the bill shape of the hummingbird pollinators but that the nature of this relationship differed between pollination specialists and generalists. For example, corolla curvature was positively correlated with bill curvature for specialists but not for generalists. Conclusions. Our study suggests that pollinators affect the evolution of flower shape but that the nature and strength of the selective pressures are affected by the pollinator guild of the pollinators in the Antillean Gesneriaceae.