Predominance of self-compatibility in hummingbird-pollinated plants in the Neotropics

Both plant traits and plant-pollinator interactions are thought to influence plant mating systems. For hummingbird-pollinated plants, foraging strategy (territorial or traplining) is also expected to influence plant mating. We hypothesize that the traplining behavior of hermits promotes outcrossing, whereas the behavior of non-hermits favours self-incompatibility. Thus, selection is expected to maintain self-incompatibility in plants pollinated by non-hermits. We explore the incidence of self-incompatibility in Neotropical hummingbird-pollinated plants and its association with hummingbird behavior and plant traits. We conducted a literature review (56 species) and performed hand-pollination experiments in 27 hummingbird-pollinated plants in an Atlantic rainforest. We found that self-incompatibility (measured as <0.3 for the Index of Self-incompatibility [ISI]) occurred in only 33 % of the Neotropical hummingbird-pollinated plants. The interaction of hummingbird and habit type affected ISI, as did phylogenetic relationships. Specifically, herbs pollinated by non-hermits had higher ISI than woody plants pollinated by non-hermits, and herbs pollinated by both hermits and non-hermits. For the Atlantic rainforest plant guild, 30 % of the species were self-incompatible. ISI was higher in herbs than in woody species and increased with plant aggregation but was not dependent on foraging behavior, plant density, or floral display. Although hummingbirds differ in their foraging strategies, these behavioral differences seem to have only a minor influence on the incidence of self-incompatibility. Phylogenetic relatedness seems to be the strongest determinant of mating system in Neotropical hummingbird-pollinated plants.