Modularity increases rate of floral evolution and adaptive success for functionally specialized pollination systems

Modularity, the relative independence of trait clusters within an organism, is a pervasive biological concept that also applies to angiosperm flowers. We test competing modularity hypotheses and assess the role of functional adaptations as well as genetic and developmental constraints in the flowers of Merianieae (Melastomataceae). This group is characterized by different pollinator selection regimes and a strong developmental constraint: tubular anthers adapted to buzz-pollination. Our analyses of tomography-based 3-D flower models show that pollinators selected for functional modules spanning across developmental units and that patterns of floral modularity became disrupted during pollinator shifts. Further, we show that modularity was crucial for Merianieae to overcome the constraint of their tubular anthers by allowing for increased rates of evolution in other flower parts. We conclude that floral modularity may be key to the adaptive success of functionally specialized pollination systems by making flowers flexible (evolvable) for adaptation to changing selection regimes.