Beyond buzz-pollination – departures from an adaptive plateau lead to new pollination syndromes

• Pollination syndromes describe recurring adaptation to selection imposed by distinct pollinators. We test for syndromes in Merianieae (Melastomataceae), which contain bee- (buzz), hummingbird-, flowerpiercer-, passerine-, bat-, and rodent-pollinated species. Further, we explore trait changes correlated with the repeated shifts away from buzz-pollination that represents an ‘adaptive plateau’ in Melastomataceae.

• We use Random Forest analyses to identify key traits associated with the different pollinators of 19 Merianieae species and estimate pollination syndromes of 42 more species. We employ morphospace analyses to evaluate the morphological diversity (disparity) among syndromes.

• We identify three pollination syndromes (‘buzz-bee’, ‘mixed-vertebrate’, ‘passerine’), characterized by different pollen expulsion mechanisms and reward types but not by traditional syndrome characters. Further, we find that ‘efficiency’ rather than ‘attraction’ traits are important for syndrome circumscription. Contrary to syndrome theory, our study supports pooling different pollinators (hummingbirds, bats, rodents, flowerpiercers) into the ‘mixed-vertebrate’ syndrome and we find that disparity is highest in the ‘buzz-bee’ syndrome.

• We conclude that the highly adaptive buzz-pollination system may have prevented shifts towards classical pollination syndromes, but provided the starting point for the evolution of a novel set of distinct syndromes, all having retained multifunctional stamens that provide pollen expulsion, reward, and attraction.