Floral Scent Composition and Fine-Scale Timing in Two Moth-Pollinated Hawaiian Schiedea (Caryophyllaceae).

John M Powers,Alex Guenther,Stephen G Weller,Diane R Campbell,Roger Seco,Celia L Faiola,Ann K Sakai

doi:10.3389/fpls.2020.01116

Abstract

Floral scent often intensifies during periods of pollinator activity, but the degree of this synchrony may vary among scent compounds depending on their function. Related plant species with the same pollinator may exhibit similar timing and composition of floral scent. We compared timing and composition of floral volatiles for two endemic Hawaiian plant species, Schiedea kaalae and S. hookeri (Caryophyllaceae). For S. kaalae, we also compared the daily timing of emission of floral volatiles to evening visits of their shared pollinator, an endemic Hawaiian moth (Pseudoschrankia brevipalpis; Erebidae). The identity and amount of floral volatiles were measured in the greenhouse during day and evening periods with dynamic headspace sampling and GC-MS (gas chromatography – mass spectrometry). The timing of emissions (daily rise, peak, and fall) was measured by sampling continuously for multiple days in a growth chamber with PTR-MS (proton transfer reaction mass spectrometry). Nearly all volatiles detected underwent strong daily cycles in emission. Timings of floral volatile emissions were similar for S. kaalae and S. hookeri, as expected for two species sharing the same pollinator. For S. kaalae, many volatiles known to attract moths, including several linalool oxides and 2-phenylacetaldehyde, peaked within 2 h of the peak visitation time of the moth which pollinates both species. Floral volatiles of both species that peaked in the evening were also emitted several hours before and after the brief window of pollinator activity. Few volatiles followed a daytime emission pattern, consistent with increased apparency to visitors only at night. The scent blends of the two species differed in their major components and were most distinct from each other in the evening. The qualitative difference in evening scent composition between the two Schiedea species may reflect their distinct evolutionary history and may indicate that the moth species uses several different floral cues to locate rewards.

Highlights

In flowering plants, attraction of pollinators is often required for reproduction, but the multimodal signals that attract pollinators are costly and require both carbon and energy (Dicke and Sabelis, 1989; Grison-Pigé et al, 2001)
We investigated the composition and timing of floral scent in Schiedea kaalae and S. hookeri (Caryophyllaceae), two hermaphroditic species with specialized floral nectaries and similar floral morphology (Wagner et al, 2005b) which are pollinated by the endemic Hawaiian moth Pseudoschrankia brevipalpis (Erebidae; Weisenberger et al, 2014; Medeiros, 2015; Weller et al, 2017)
Using GC-MS we detected 32 floral volatiles produced by S. kaalae and 36 produced by S. hookeri, for a total of 40 volatiles present in > 20% of samples of either species

Summary

Introduction

Attraction of pollinators is often required for reproduction, but the multimodal signals that attract pollinators are costly and require both carbon and energy (Dicke and Sabelis, 1989; Grison-Pigé et al, 2001). The fitness of Nicotiana attenuata plants is affected if the timing of flower orientation or olfactory pollination cues is altered physically or genetically (Baldwin et al, 1997; Yon et al, 2017). Overlap between the window of pollinator activity and the timing of floral signals is common, whether the signals are related to physical access (Overland, 1960; Goldblatt et al, 2004), flower orientation (Yon et al, 2017), or scent production (Heath et al, 1992; Huber et al, 2004; Effmert et al, 2005; Kumano and Yamaoka, 2006; Okamoto et al, 2008; Prieto-Benıtez et al, 2016; Chapurlat et al, 2018)

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Conclusion