Bees and evolution of occluded corollas in snapdragons and relatives (Antirrhineae)

The tribe Antirrhineae is a natural group comprising 28 genera and over 320 species. In most Antirrhineae the corolla is marked by the development of a prominent palate (personate flower) that sometimes occludes the entrance of the corolla tube. Traditionally strong bees of different size have been considered as the principal pollinators of occluded, personate flowers (snapdragon-type). Phylogenetic analyses (ITS and ndhF regions) were conducted to gain insight into evolutionary changes in personate flower and corolla occlusion. In addition, logistic regressions were performed in order to test the role of this type of flower as a floral filtering morphology for pollinators. Historical reconstruction of the personate flower supports its ancestral condition within Antirrhineae and a general pattern of recurrent corolla occlusion shifts have prevailed since lineage diversification of the Antirrhineae. In addition, we found some evidence of snapdragon-type corollas negatively affecting hummingbirds and insects other than bees. Part of this outcome is due to predominance of bees as single visitors of Antirrhineae species with closed corollas (c. 65% of the species). The lack of significant correlation between bees and occluded, personate flowers is interpreted as the ability of bees of visiting any type of flowers. The personate flower, particularly when occluded, displays one of the most specialized corollas in pollinator exclusion by physical barriers. (C) 2015 Geobotanisches Institut ETH, Stiftung Ruebel. Published by Elsevier GmbH. All rights reserved.