The relationship between floral nectar composition and visitors in Lycium (Solanaceae) from Argentina and Chile: what does it reflect?

Abstract

We evaluated the relationship between floral nectar composition, flower visitors, and floral form for Lycium species from Argentina and Chile. Our goal was to determine whether nectar chemical composition is correlated with floral form and pollinators or whether it is a conservative character. We analysed 54 populations from 14 species and six varieties. This sample is representative of the floral variation in the genus, and the taxa come from its main area of diversification. The nectar of all the taxa contains both amino acids and sugars. The mean nectar sugar concentration is high: 48.4% ± 19.8. There is a remarkable constancy in the nectar sugar ratio among the taxa: 90% of them present a hexose dominant one, i.e. nectar has <10% sucrose and >90% fructose and glucose. Visitors include Hymenoptera, Diptera, and Lepidoptera; the most common family of each order is Anthophoridae, Syrphidae, and Nymphalidae, respectively. Only one species is visited by hummingbirds. Most of the plant taxa (68.4%) are visited by members of two or three insect orders. No patterns have been detected between the kinds of visitors and the flower morphology. The homogeneity of nectar sugar composition in contrast to the variety of visitors and flower forms indicates that there is no correlation between the nectar sugar ratio and floral form or pollinators. This suggests that nectar ratio is a conservative character in Lycium .