Ontogenetic Mechanisms of Differentiation in Two Salvia Species With Different Pollinators

Shifts between pollinators are a major driver in the evolution and diversification of angiosperms and often involve major changes in flower morphology. These morphological differences typically originate during development, highlighting the importance of integrating ecological and developmental studies. Corolla tube length, in particular, is a key trait in specialized plant-pollinator interactions. Here, we compared flower development in two closely related Salvia species with contrasting corolla tube lengths: Salvia guaranitica, pollinated by hummingbirds, and Salvia stachydifolia, primarily pollinated by bees. We characterized developmental trajectories, floral development duration, and patterns of cell growth and proliferation. Both species shared similar allometric trajectories, differing only in their prolongation, suggesting ontogenetic scaling. However, S. guaranitica exhibited longer and faster corolla tube growth, resulting in a larger final size compared to S. stachydifolia. Corolla tube growth was linked to cell proliferation during the early stages of bud development and rapid anisotropic cell elongation in later stages. Additionally, we observed differences in anisotropic growth rates across basal, middle, and distal regions of the corolla tube. These findings suggest that shifts between pollination syndromes in Salvia species may occur without major changes to basic developmental patterns, but through ontogenetic scaling accompanied by heterochronic changes.