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

Hannelise de Kassia Balduino; Priscila Tunes; Emanuele Giordano; Massimo Guarnieri; Silvia Rodrigues Machado; Massimo Nepi; Elza Guimarães

doi:10.1093/aobpla/plac067

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

AoB Plants. 2022 Dec 30;15(2):plac067. doi: 10.1093/aobpla/plac067. eCollection 2023 Feb.

Authors

Hannelise de Kassia Balduino^{1

2}, Priscila Tunes², Emanuele Giordano³, Massimo Guarnieri³, Silvia Rodrigues Machado⁴, Massimo Nepi^{3

5}, Elza Guimarães²

Affiliations

¹ Graduate Course in Plant Biology, São Paulo State University, 18618-689 Botucatu, Brazil.
² Laboratory of Ecology and Evolution of Plant-Animal Interactions, Institute of Biosciences, São Paulo State University, 18618-689 Botucatu, Brazil.
³ Laboratory of Analytical Methods for Chemical Ecology - Plant Reproductive Biology, Department of Life Sciences, University of Siena, 53100 Siena, Italy.
⁴ Laboratory of Plant Anatomy, Institute of Biosciences, São Paulo State University, 18618-689 Botucatu, Brazil.
⁵ National Biodiversity Future Center (NBFC), 90133 Palermo, Italy.

Abstract

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 γ-aminobutyric acid and β-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.

Keywords: Amino acids; Amphilophium mansoanum; ants; bee pollination; extranuptial nectary; nectar chemical composition; nectar secretion dynamics; neuroactive specialized metabolites; nuptial nectary.