Floral Scent and Pollinators of Cypripedium calceolus L. at Different Latitudes

Herbert Braunschmid,Stefan Dötterl,Robin Guilhot

doi:10.3390/d13010005

Abstract

Floral scent is an important trait in plant–pollinator interactions. It not only varies among plant species but also among populations within species. Such variability might be caused by various non–selective factors, or, as has been shown in some instances, might be the result of divergent selective pressures exerted by variable pollinator climates. Cypripedium calceolus is a Eurasian deceptive orchid pollinated mainly by bees, which spans wide altitudinal and latitudinal gradients in mainly quite isolated populations. In the present study, we investigated whether pollinators and floral scents vary among different latitudes. Floral scents of three C. calceolus populations in the Southern Alps were collected by dynamic headspace and analyzed by gas chromatography coupled to mass spectrometry (GC/MS). These data were completed by previously published scent data of the Northern Alps and Scandinavia. The scent characteristics were compared with information on pollinators recorded for present study or available in the literature. More than 80 scent compounds were overall recorded from plants of the three regions, mainly aliphatics, terpenoids, and aromatics. Seven compounds were found in all samples, and most samples were dominated by linalool and octyl acetate. Although scents differed among regions and populations, the main compounds were similar among regions. Andrena and Lasioglossum species were the main pollinators in all three regions, with Andrena being relatively more abundant than Lasioglossum in Scandinavia. We discuss natural selection mediated by pollinators and negative frequency–dependent selection as possible reasons for the identified variation of floral scent within and among populations and regions.

Highlights

Animals can drive divergent evolution in plants by applying different selective pressures on plant traits when pollinating them [1,2,3,4]
The flower scent of C. calceolus along a latitudinal gradient from south of the Alps to Scandinavia contained in a total of 85 compounds, most of which were identified (Table 1)
A Kovats retention index; not available for compounds which were only found in the Scandinavian sample; b Compounds within classes are ordered according to Kovats retention index; c Bergström et al [18] recorded mean values based on several samples and we indicate just the presence of a compound; d Compound identification verified through authentic standard; e For Uppsala, Scandinavia these are mean relative amounts taken from Bergström et al [18]; f coefficient of variation (CV) (Coefficient of variation) calculated from semi–quantitative data (NA: not applicable); values for Uppsala, Scandinavia are not available; g Unknowns are pooled with the superscript digit giving the number of pooled compounds. *: values >0 and

Summary

Introduction

Animals can drive divergent evolution in plants by applying different selective pressures on plant traits when pollinating them [1,2,3,4]. At least three different scenarios in which pollinator–mediated selection leads to variation in scent (and other) traits are discussed in literature [9]. Different pollinator climates may lead to interspecific reproductive isolation, potentially followed by divergent speciation and variations in scents among populations/species. This especially is true if locally available pollinators differ in their olfactory preferences. In species with male and female flowers, the selective pressures mediated by pollinators might be different among the sexes, leading to intersexual morph variation [9]

Methods

Results

Conclusion