Nocturnal Bee Pollinators Are Attracted to Guarana Flowers by Their Scents.

Cristiane Krug,Irmgard Schäffler,Isabel Alves-Dos-Santos,Claudia I Silva,Reisla Oliveira,Stefan Dötterl,Guaraci D Cordeiro,Clemens Schlindwein

doi:10.3389/fpls.2018.01072

Abstract

Floral scent is an important component of the trait repertoire of flowering plants, which is used to attract and manipulate pollinators. Despite advances during the last decades about the chemicals released by flowers, there is still a large gap in our understanding of chemical communication between flowering plants and their pollinators. We analyzed floral scents of guarana (Paullinia cupana, Sapindaceae), an economically important plant of the Amazon, using chemical analytical approaches, and determined the attractiveness of the scent to its nocturnal bee pollinators using behavioral assays in the field. Pollen loads of attracted bees were also analyzed. Inflorescences of guarana emit strong scents, both during day and at night, with some semi-quantitative differences between day- and night-time scents. Synthetic scent mixtures containing some of the identified floral scent components, including the most abundant ones, i.e., linalool and (E)-β-ocimene, successfully attracted the nocturnal Megalopta bee pollinators. Pollen analyses revealed that many of the attracted bees had pollen grains from previous visits to guarana flowers on their bodies. Overall, our data show that guarana flowers attract nocturnal bee visitors by their strong scents and suggest that the chemical communication between this plant and its pollinators is a key component in crop production of this economically important plant species.

Highlights

Floral scents are important signals for the attraction of pollinators and may be important for plants pollinated at night when visual signals are of limited use
We addressed the following questions: What are the absolute amounts of floral scents released, and does scent differ between day and night in quantitative and compositional properties? Are there differences in scent between pistillate and staminate flowers? Are nocturnal/crepuscular bees attracted by the main floral scent components, and if yes, do they carry pollen grains from previous visits to guarana flowers on their bodies?
Our study shows that inflorescences of guarana emit strong scents, which do not differ in quantitative and semi-quantitative properties between the sexual phases, but do differ in semiquantitative properties between day- and night-time

Summary

Introduction

Floral scents are important signals for the attraction of pollinators and may be important for plants pollinated at night when visual signals are of limited use. A new pollination system mediated by floral scent and involving nocturnal bees as pollinators was described (Cordeiro et al, 2017). The nocturnal/crepuscular habit has arisen in four families of bees, i.e., Andrenidae, Apidae, Colletidae, and Halictidae, comprising at least 250 species (Warrant, 2007). It is hypothesized that night-active bees evolved this habit as a response to competition, parasitism, and predation during the day (Wcislo et al, 2004). Foraging at night and during crepuscular periods may be beneficial

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