Floral trait convergence and functional differentiation concomitant with pollinator shifts in Merianieae (Melastomataceae)

Agnes Dellinger, Silvia Artuso, Diana Fernández-Fernández, Darin S. Penneys, FA Michelangeli, Marcela Alvear, F Almeda, Yannick Städler, Jürg Schönenberger

Flowers are complex and highly integrated structures with different types of organs co-functioning to achieve pollinator attraction and pollen transfer. Relative independence (modularity) of some organs from others (e.g., perianth organs from reproductive organs) has been thought to increase the potential for adaptive evolution. Modules themselves, however, may change their function if selection pressures change, e.g. due to pollinator shifts from one functional group of pollinators to another. Our study focuses on the Neotropical tribe Merianieae (Melastomataceae) as a model system for the study of pollinator mediated selection on floral traits. The Merianieae are characterized by repeated independent shifts from bee to hummingbird/bat/rodent, and passerine pollination, respectively. We combine qualitative trait mapping of 40 floral traits relevant for pollination with a High Resolution X-ray Computed Tomography-based 3D-geometric morphometric assessment of flowers across 60 Merianieae species. Our goals are (i) to pinpoint functional trait differentiation in pollen transfer mechanisms between the different pollination systems and (ii) to test hypotheses on changes in patterns of modularity. Our analyses show a clear differentiation in floral shape and function in relation to the different functional pollinator groups. Particularly strongly affected floral traits associated with the different pollinators include reward type, stamen appendage shape, thecal wall structure, location of pollen chamber and size of staminal pores. We describe a clear functional differentiation in pollen expulsion and deposition mechanisms including elaborate vibratile buzz-pollination in bee pollinated systems, saltshaker-like pollen release upon stamen contact in hummingbird/bat/rodent pollinated species, and pollen release by a specialized "bellows"-mechanism in passerine pollinated species. Furthermore, geometric morphometric analyses of 3D landmark data highlight changes in patterns of floral integration and modularity, with changes of corolla function associated with shifts from bee to bird pollination, and a loss in function of stamen appendages as triggers of pollen expulsion mechanisms in hummingbird pollinated species

Department of Botany and Biodiversity Research
External organisation(s)
California Academy of Sciences
Publication date
Austrian Fields of Science 2012
106042 Systematic botany, 106008 Botany, 106012 Evolutionary research
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