Stickiness of plant leaf tissue is not a rare phenomenon and has evolved multiple times in different families. This stickiness is widely hypothesized as a defense against herbivores. Thus, it can come with significant ecological costs when expressed in flowers, where it can compromise interactions with mutualist pollinators, especially when they are insects. Bejaria resinosa is a tropical Ericaceae species that is polymorphic for the expression of stickiness on flower petals. Bejria resinosa is visited by hummingbirds, bees and bumblebees and is attack by avian flower piercers and insect florivores. On sticky flowers, it is common to find corpses of bees, wasps and butterflies that are all potential pollinators or herbivores. We conducted a functional and mechanistic analysis of floral stickiness in this species. Initially, we hypothesized that stickiness functions as a defense against bird piercers and florivores. We used a survey of three different populations of B. resinosa and a manipulative experiment to establish a causal link between stickiness in flowers and the damage plants receive from flower piercers and florivores. We found that one moth larvae consumed the internal structures of the flower, we also surveyed the proportion of flowers affected by this larva. To test if stickiness has an effect on fitness the fruit set was quantified. Moreover, we began to identify the chemical composition of the sticky substance covering floral petals of some of the plants in the populations.
Results/Conclusions
We demonstrate that stickiness does not reduce the proportion of flowers pierced, but there is a significant reduction in florivory underlining the repellency of stickiness for arthropods but not for birds. The damage made by a specialist moth is also lower in the sticky plants. Fruit set was higher only in one population, and not different in the other two. We hypothesize that this pattern is due to the presence of hummingbirds and further discuss arising ecological conflicts between pollination and herbivory as well as alternative functions of floral stickiness.