The tremendous diversity of angiosperm flowers has most likely evolved primarily in connection with their manifold pollinators. A particularly interesting topic located at the interface of pollination ecology and floral evolution is the occurrence of so-called pollinator shifts, i.e., the shift from one functional group of pollinators to another (e.g., from bees to birds). This project focuses on a group of Central- and South American plants (the tribe Merianieae) belonging to the melastome family (Melastomataceae). The Merianieae include bee-, bat-, hummingbird- as well as passerine pollinated species. Using high resolution x-ray computed tomography combined with geometric morphometrics, we aim at analyzing in detail the differences in floral traits associated with different functional groups of pollinators. In addition, using a population genetic approach, we will assess gene flow and pollination efficiency in the different pollination systems.