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

Abstract

Background and aims 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. Methods 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 (DC.) L.G.Lohmann (Bignoniaceae). For that we characterised nectar sugar, amino acid, and specialised metabolite composition by HPLC. Key results 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 γ-amino butyric acid and β-amino butyric 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 specialised metabolite tyramine. Conclusions The nectar traits from nuptial and extranuptial nectaries differ in energy amount and nutritional value, as well as in neuroactive specialised 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.

Specialized pollination by cecidomyiid flies and associated floral traits in Vincetoxicum sangyojarniae (Apocynaceae, Asclepiadoideae)

“…2017; Balduino et al . 2023). The flowers of V. sangyojarniae secrete a small volume of highly viscous nectar, in which sucrose is the only sugar contained in the samples from all study sites.…”

“…sucrose and its component hexoses, glucose and fructose, although both interspecific and intraspecific variation in proportions of these sugars often occur (Baker & Baker 1983;Nicolson 2022). Nectar sugar composition may greatly influence the preference of insect foragers (Roy et al 2017;Balduino et al 2023). The flowers of V. sangyojarniae secrete a small volume of highly viscous nectar, in which sucrose is the only sugar contained in the samples from all study sites.…”