Does florivory affect the attraction of floral visitors to buzz-pollinated Solanum rostratum?

Abstract

Floral herbivory (florivory) can directly and indirectly affect plant reproduction through the loss of ovules or seeds and by reducing the visitation by pollinators through the reduction in flower attractiveness, respectively. We studied the effect of florivory on pollinator visitation in a buzz-pollinated herb. We used Solanum rostratum as the study model because its specialised morphology, heterantherous flowers that emit floral scents, demands a close association with its pollinators (buzzing bees). We hypothesized that when florivores consume the attractive structures (corolla and rewarding anthers), the pollinators would visit the damaged flowers less often, indirectly affecting S. rostratum reproductive success. Furthermore, we hypothesized that consumption of the reproductive structures (pollinating anther and pistil) would directly affect the plants reproductive success. We conducted observations of three S. rostratum populations in central Mexico. We observed twelve species of florivore consuming S. rostratum flowers. Florivores preferred to consume the attractive structures (corolla) over reproductive structures. However, they preferred to consume the anthers specialised for feeding pollinators over the anthers specialised for pollination. In addition, we recorded floral volatiles emitted by flowers damaged by florivory using solid-phase microextraction coupled with gas chromatography–mass spectrometry. We identified 25 volatile compounds in S. rostratum flowers, mainly aromatic, monoterpene and sesquiterpene compounds. The relative proportions of these compounds differed between undamaged and damaged flowers. Bioassays showed that both legitimate visitors (pollinators) and illegitimate visitors (thieves) visited undamaged flowers more often than flowers damaged by florivores; however, the decrease in visitation frequency did not affect fruit and seed production. In conclusion, the consumption of attractive (corolla) and reward floral structures (feeding anthers) reduced the frequency of visits by pollinators but does not affect S. rostratum reproductive success (fruit and seed set) probably because reproductive structures (pistil and pollinating anthers) are less often consumed.