Evolutionary breakdown of pollination specialization in a Caribbean plant radiation

Ecological generalization is postulated to be the rule in plant-pollinator interactions; however, the evolution of generalized flowers from specialized ancestors has rarely been demonstrated. This study examines the evolution of pollination and breeding systems in the tribe Gesnerieae (Gesneriaceae), an Antillean plant radiation that includes specialized and generalized species. Phylogenetic reconstruction was based on two nDNA markers (internal transcribed spacer (ITS) and G-CYCLOIDEA (GCYC) and morphology. The total evidence Bayesian phylogeny was used for assessment of floral character evolution using Bayesian stochastic character mapping. Mapping of the pollination system resulted in at least two origins of bat pollination and two origins of generalized pollination (bats, moths and hummingbirds). The evolution of bat pollination was associated with floral transitions reflecting the chiropterophilous floral syndrome. The evolution of generalization was associated with subcampanulate corollas. Autonomous breeding systems evolved only in hummingbird-pollinated lineages. The correlated evolution of floral traits and pollination systems provides support for the pollination syndrome concept. Floral transitions may have been favored by the low frequency of hummingbird visitation in the Antilles, while the presence of autonomous pollination may have allowed the diversification of ornithophilous lineages. Results suggest that pollinator depauperate faunas on islands select for the evolution of reproductive assurance mechanisms, including generalization and autogamy.