Generalized pollination system: are floral traits adapted to different pollinators?

Abstract

Flowers that are pollinated both during the day and at night could exhibit two different groups of pollinators and produce two different sets of attractants and rewards. We explored the patterns of emission of flower scents and production of nectar in the cactus Echinopsis chiloensis ssp. chiloensis, in relation to the patterns of activity of its diurnal and nocturnal pollinators. We measured frequency of flower visitors, analyzed floral scents, measured nectar production and sugar concentration, and performed pollination exclusion experiments. Bees were the main visitors at daytime and hawkmoths at nighttime. Diurnal scents were dominated by several compounds that can attract a wide range of pollinators, whereas nocturnal scents were less diverse and were dominated by (E)-nerolidol, a compound eliciting antennal responses in hawkmoths. Nectar volume and sugar concentration at night were similar to those recorded in hawkmoth-pollinated flowers. Daytime nectar volume was higher than those commonly found in bee-pollinated flowers, but similar to those found in flowers pollinated by several pollinators. Daytime sugar concentration was similar to those recorded in bee-pollinated flowers. Flowers of E. chiloensis ssp. chiloensis seem morphologically adapted to hawkmoth pollination, but diurnal and nocturnal pollinators contribute to similar extents to reproductive success. Additionally, diurnal and nocturnal pollinators showed a synergic effect on the product of fruit set and seed set. The results are discussed in terms of the linkage between floral traits and perception abilities and requirements of pollinators