Abstract
Summary Pollination syndromes describe recurring adaptation to selection imposed by distinct pollinators. We tested for pollination syndromes in Merianieae (Melastomataceae), which contain bee‐ (buzz‐), hummingbird‐, flowerpiercer‐, passerine‐, bat‐ and rodent‐pollinated species. Further, we explored trait changes correlated with the repeated shifts away from buzz‐pollination, which represents an ‘adaptive plateau’ in Melastomataceae.We used random forest analyses to identify key traits associated with the different pollinators of 19 Merianieae species and estimated the pollination syndromes of 42 more species. We employed morphospace analyses to compare the morphological diversity (disparity) among syndromes.We identified three pollination syndromes (‘buzz‐bee’, ‘mixed‐vertebrate’ and ‘passerine’), characterized by different pollen expulsion mechanisms and reward types, but not by traditional syndrome characters. Further, we found that ‘efficiency’ rather than ‘attraction’ traits were important for syndrome circumscription. Contrary to syndrome theory, our study supports the pooling of different pollinators (hummingbirds, bats, rodents and flowerpiercers) into the ‘mixed‐vertebrate’ syndrome, and we found that disparity was 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.
Highlights
The observation of recurring floral phenotypes associated with distinct pollinator groups has given rise to the concept of pollination syndromes (Delpino, 1890; Vogel, 1954; Stebbins, 1970; Faegri & van der Pijl, 1979; Endress, 1996)
Based on earlier studies of pollination syndromes (e.g. Ollerton et al, 2009) and on floral morphology in Melastomataceae (e.g. Varassin et al, 2008; Mendoza-Cifuentes & FernandezAlonso, 2010; Cotton et al, 2014; Dellinger et al, 2014), we have compiled a list of 61 floral characters potentially important for pollination
Classification of the 19 species with known pollinators (Table 1) into six syndromes (‘buzz-bee’, ‘hummingbird’, ‘hummingbird/ bat’, ‘hummingbird/rodent’, ‘flowerpiercer/rodent’ and ‘passerine; ‘six-syndrome model’) using OOB data led to an overall median error rate of 31% over all 100 random forests (RF)
Summary
The observation of recurring floral phenotypes associated with distinct pollinator groups has given rise to the concept of pollination syndromes (Delpino, 1890; Vogel, 1954; Stebbins, 1970; Faegri & van der Pijl, 1979; Endress, 1996). Pollinators are grouped into functional categories, i.e. groups of animals probably exerting similar selective pressures on flowers as a result of shared morphology, foraging behaviour/preferences and sensory abilities (Fenster et al, 2004). Flowers pollinated by the same functional group of pollinators are expected to converge onto similar phenotypes in response to selection imposed by the most effective pollinators Besides selection generated by pollinator effectiveness, the evolution of floral traits may be mediated by antagonistic interactions (e.g. red coloration as bee avoidance in hummingbird flowers; Papiorek et al, 2014), competition for
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