Floral and Extrafloral Nectars of Costa Rican Inga Trees: A Comparison of their Constituents and Composition

Abstract

Two types of nectaries occur in the neotropical genus Inga (Fabaceae: Mimosoideae). Floral nectar is ingested by visitors to flowers and foliar nectar is utilized by a variety of insects. Although their flowers are similar in appearance and morphology, different Inga species exhibit different floral behaviors and have different primary pollinators. The floral nectars of the eight species analyzed are, however, similar in proportions of various sugars. Freshly secreted floral nectars are sucrose-dominant, though over time the sucrose is hydrolyzed and nectars become hexose-rich. In some species, this change corresponds to a shift in the pollinator fauna. Amino acid constituents of floral nectars differ among Inga spp., but are constant within a species. Extrafloral nectars are hexose-dominant and have substantially greater sugar concentrations than floral nectars. Extrafloral nectars of different species differ in array of amino acids present, but amino acids in floral and extrafloral nectar of a given species are similar, but not identical. Differences in composition of the two types of nectar produced by a given Inga species may result from natural selection by mutualists utilizing the nectar as well as non-evolutionary influences of the abiotic and biotic environment.