To each their own! Nectar plasticity within a flower mediates distinct ecological interactions

Our results highlight the plasticity of nectar traits underlying the diversity of nectaries within a plant, which mediates distinct ecological interactions. Nuptial nectaries are exclusively visited by bees and extranuptial nectaries by ants, cockroaches, wasps and flies. Nectar from these nectaries differ in energy amount, nutritional value and neuroactive specialized metabolites. The specificity of visitors' taxa between distinct nectaries may be due to plant-driven differences in nectar chemical composition. Nevertheless, as all floral visitors exclusively consume only one of the two nectar types, they are prone to exert selective pressures upon nectar traits, selecting those that fit their specific preferences.Nuptial and extranuptial nectaries are involved in interactions with different animal functional groups. Nectar traits involved in pollination mutualisms are well known. However, we know little about those traits involved in other mutualisms, such as ant-plant interactions, especially when both types of nectaries are in the same plant organ, the flower. Here we investigated if when two types of nectaries are exploited by distinct functional groups of floral visitors, even being within the same plant organ, the nectar secreted presents distinct features that fit animal requirements. We compared nectar secretion dynamics, floral visitors and nectar chemical composition of both nuptial and extranuptial nectaries in natural populations of the liana Amphilophium mansoanum (Bignoniaceae). For that we characterized nectar sugar, amino acid and specialized metabolite composition by high-performance liquid chromatography. Nuptial nectaries were visited by three medium- and large-sized bee species and extranuptial nectaries were visited mainly by ants, but also by cockroaches, wasps and flies. Nuptial and extranuptial nectar differed regarding volume, concentration, milligrams of sugars per flower and secretion dynamics. Nuptial nectar was sucrose-dominated, with high amounts of gamma-aminobutyric acid and beta-aminobutyric acid and with theophylline-like alkaloid, which were all exclusive of nuptial nectar. Whereas extranuptial nectar was hexose-rich, had a richer and less variable amino acid chemical profile, with high amounts of serine and alanine amino acids and with higher amounts of the specialized metabolite tyramine. The nectar traits from nuptial and extranuptial nectaries differ in energy amount and nutritional value, as well as in neuroactive specialized metabolites. These differences seem to match floral visitors' requirements, since they exclusively consume one of the two nectar types and may be exerting selective pressures on the composition of the respective resources of interest.