Floral scent and pollinator interactions of three species in Isabela Island (Galapagos)

The study focused on examining the chemical composition of floral scents and the insect visitors of three species of Asteraceae endemic to the Galapagos archipelago: Scalesia affinis, Darwiniothamnus lancifolius, and Darwiniothamnus tenuifolius. These species inhabit different zones, with S. affinis found in dry areas and the Darwiniothamnus species in humid areas. Each species displayed a distinct scent and pollinator profile. Scalesia affinis emits a floral scent dominated by the monoterpene & alpha;-pinene, and its primary pollinators, nearly exclusive to the species, are the female carpenter bees Xylocopa darwini (Hymenoptera). Darwiothamnus lancifolius and D. tenuifolius exhibited a complex mixture of floral aroma compounds. Both species were characterized by a significant presence of sesquiterpenes, particularly aristolene. In D. tenuifolius, benzaldehyde and indole were also abundant. This aromatic profile appears to attract dipterans, the predominant group of pollinators in elevated and humid regions. This study is the first to investigate the chemical composition of floral scents in plants from the Galapagos Islands and their relationship with entomophily.