Supplementary material from "Low-level ethanol is widespread within floral nectar"

Floral nectar is a major part of the diet of many animals, which can consume daily nectar volumes equivalent to their body mass. Saccharide-rich nectar may undergo fermentation after becoming inoculated with microbes, yet empirical studies surveying nectar-alcohol concentrations are sparse. We used an enzymatic assay to estimate ethanol concentrations for 147 samples of nectar from 29 species of flowering plants at a botanical garden. Ethanol was detected within 48% of all nectar samples, with at least one ethanolic sample for 26 species. Ethanol-positive samples contained concentrations averaging 0.016% (weight/weight) by species, with a maximum species average of 0.032% and a maximum sample concentration of 0.056%. The resulting estimated body mass-adjusted daily ethanol dosage for associated pollinators is considerable, roughly comparable to a single alcoholic beverage consumed by a 70 kg human over the course of a day. Additional field and metabolic studies are needed to determine to what extent such ethanol concentrations are either physiologically or ecologically relevant for animal consumers. Overall, our results indicate that exposure to low levels of ethanol amongst nectarivores is likely to be widespread.