EVOLUTION OF FLORAL MORPHOLOGY AND SYMMETRY IN THE MICONIEAE (MELASTOMATACEAE): MULTIPLE GENERALIZATION TRENDS WITHIN A SPECIALIZED FAMILY

摘要

Premise of research. Analyses of the evolution of floral morphology and symmetry broaden our understanding of the drivers of angiosperm diversification. Integrated within a flower, labile floral characters produce different phenotypes that promote variable interactions with pollinators. Thus, investigation of floral evolution may help with inferring potential historic transitions in pollinator modes and ecological pressures that generated present diversity. This study aims to explore the morphological evolution of flowers in Miconieae, a species-rich Neotropical tribe within the Melastomataceae. Despite a constrained floral plan, Melastomataceae manage to achieve a variety of floral phenotypes appealing to diverse pollinator types, with a majority of the species requiring specialized "buzz pollination" by bees. However, previous research of Miconieae documented several instances of convergent evolution of phenotypes associated with generalized pollination strategies. We explore the floral morphological evolution of Miconieae in a phylogenetic context to understand how diversification relates to different phenotypes and how common evolution of generalized pollination systems is within this tribe. Methodology. We constructed the largest species-level phylogeny of the Miconieae and combined it with morphological data on a variety of floral characteristics for more than 350 species scored from field photographs. Trait evolution was then analyzed using ancestral state reconstruction with stochastic character mapping. Trait correlation was estimated with Pagel's statistical method for discrete characters and with regression analysis of phylo-genetically independent contrasts of continuous characters. We analyzed diversification in the tribe with Bayesian analysis of macroevolutionary mixtures and explored the effect of character state evolution on diversification with the binary state speciation and extinction approach. Pivotal results. Our analyses reveal rampant convergent and correlated evolution of multiple characters indicative of pollinator-mediated selective pressures. Conclusions. We confirm several parallel trends in the evolution of generalized floral phenotypes and find an association between generalization trends and increased diversification rates that may be related to colonization of highland environments.