Abstract
Floral chemistry mediates plant interactions with herbivores, pathogens, and pollinators. The chemistry of floral nectar and pollen, the primary food rewards for pollinators, can affect both plant reproduction and pollinator health. Although the existence and functional significance of nectar and pollen secondary metabolites has long been known, comprehensive quantitative characterizations of secondary chemistry exist for only a few species. Moreover, little is known about intraspecific variation in nectar and pollen chemical profiles. Because the ecological effects of secondary chemicals are dose-dependent, heterogeneity across genotypes and populations could influence floral trait evolution and pollinator foraging ecology. To better understand within- and across-species heterogeneity in nectar and pollen secondary chemistry, we undertook exhaustive LC-MS and LC-UV-based chemical characterizations of nectar and pollen methanol extracts from 31 cultivated and wild plant species. Nectar and pollen were collected from farms and natural areas in Massachusetts, Vermont, and California, USA, in 2013 and 2014. For wild species, we aimed to collect 10 samples from each of three sites. For agricultural and horticultural species, we aimed for 10 samples from each of three cultivars. Our data set (1,535 samples, 102 identified compounds) identifies and quantifies each compound recorded in methanolic extracts, and includes chemical metadata that describe the molecular mass, retention time, and chemical classification of each compound. A reference phylogeny is included for comparative analyses. We found that each species possessed a distinct chemical profile; moreover, within species, few compounds were found in both nectar and pollen. The most common secondary chemical classes were flavonoids, terpenoids, alkaloids and amines, and chlorogenic acids. The most common compounds were quercetin and kaempferol glycosides. Pollens contained high concentrations of hydroxycinnamoyl-spermidine conjugates, mainly triscoumaroyl and trisferuloyl spermidine, found in 71% of species. When present, pollen alkaloids and spermidines had median nonzero concentrations of 23,000μmol/L (median 52% of recorded micromolar composition). Although secondary chemistry was qualitatively consistent within each species and sample type, we found significant quantitative heterogeneity across cultivars and sites. These data provide a standard reference for future ecological and evolutionary research on nectar and pollen secondary chemistry, including its role in pollinator health and plant reproduction. Data are published under a Creative Commons Attribution License (CC BY 3.0 US) and may be freely used if properly cited.
Highlights
Floral nectar and pollen provide rewards for the services of pollinators
Secondary chemistry was qualitatively consistent within each species and sample type, we found significant quantitative heterogeneity across cultivars and sites
Previous studies of secondary metabolites in floral rewards have typically focused on one or ev several metabolites in one or a few plant species, such as aconitine alkaloids in Aconitum spp. (Barlow et al 2017), cardenolides in Asclepias spp. (Manson et al 2012), iridoid glycosides in Chelone glabra (Richardson et al 2016), grayanotoxins in Rhododendron ponticum (Egan et al 2016), gelsemine in Gelsemium sempervirens (Adler and Irwin 2012), or nicotine in Nicotiana spp. (Adler et al 2006, 2012)
Summary
Floral nectar and pollen provide rewards for the services of pollinators. these rewards face multiple and sometimes conflicting selective pressures to attract pollinators, and to defend against exploitation by folivores, nectar robbers, and microbes that can cause nutrient degradation and plant disease (Dobson and Bergstrom 2000, Heil 2011, McArt et al 2014). To fill some of these knowledge gaps, we present data on methanol-soluble nectar and pollen secondary metabolites from 31 wild, horticultural, and crop species This dataset is unique in its combination of diverse plant taxa, specific and exhaustive identification and quantification of methanolsoluble secondary compounds, and explicit consideration of intraspecific variation in chemical composition. Intraspecific variation was accounted for by sampling with replication from multiple sites (for wild species), and varieties and cultivars (for horticultural and crop species) We predict that these data will be a useful reference in future investigations of (i) the chemistry of individual species, (ii) the bioactivity of specific compounds and mixtures, and (iii) in phylogenetic comparisons across taxa, and thereby further the understanding of the ecological and evolutionary pressures that shape the chemistry of floral rewards
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