FLORAL NECTAR SUGAR COMPOSITION AND POLLINATOR TYPE AMONG NEW WORLD GENERA IN TRIBE ANTIRRHINEAE (SCROPHULARIACEAE)

Abstract

The floral nectar sugar compositions of 20 New World species from 10 genera and of five interspecific hybrids in tribe Antirrhineae have been analyzed using high‐performance liquid chromatography. Species are pollinated by short‐tongued bees, long‐tongued bees, and hummingbirds. Ornithophily represents the derived condition in the tribe and has arisen independently in subtribes Maurandyinae and Gambeliinae. All nectars analyzed are sucrose‐dominant or ‐rich, except for the hexose‐rich nectar of Mohavea breviflora. Despite the predominance of sucrose, floral nectar sugars from species pollinated by different pollen vectors have characteristic constituents. Nectar sugars from flowers visited by hummingbirds average 76.2% sucrose and have compositions remarkably similar to hummingbird nectars analyzed in previous studies of unrelated species. Long‐tongued bee nectars average 87% sucrose and differ from shorttongued bee nectars which have the lowest mean sucrose percentage (40.2%). The association of sugar constituent types and principal pollinators is concordant with previous data and supports hypotheses concerning pollinator preferences and the adaptive significance of certain nectar sugar compositions. Within this adaptive framework, phylogenetic constraint is also operative and may explain the predominance of sucrose in nectar sugars, similarities in sugar composition among hummingbird nectars in subtribes Maurandyinae and Gambeliinae, and the similarity of nectar from Galvezia leucantha (long‐tongued bee‐pollinated) to hummingbird‐pollinated species also in subtribe Gambeliinae.