Floral scent chemistry of sympatric species of Philodendron (Araceae) sharing a common pollinator in the fragmented coastal Atlantic Forest of southeastern Brazil

Abstract

Floral volatiles are crucial components in flower advertisement, often contributing to the reproductive isolation of angiosperms through scent-mediated differential pollinator attraction. Recently, there were significant advances in our understanding of the chemical communication between plants and cyclocephaline beetles, a predominant group of Neotropical pollinators. However, details on how the floral scent chemistry differs or converges among species pollinated by different or the same cyclocephaline beetle species are still unknown. Here, we used dynamic headspace sampling and gas chromatography coupled with mass spectrometry to investigate the floral fragrance chemistry of eight co-flowering Philodendron (Araceae) species that share a single pollinator, Cyclocephala variolosa (Melolonthidae, Cyclocephalini). Additionally, we compared our results to published data on the floral fragrances of different conspecifics pollinated by other species of cyclocephaline beetles. Although all the investigated Philodendron spp. emitted perceivably intense floral scents, the number of volatile organic compounds in the analyzed samples varied between 1 and 50 among species. Also, the overall relative scent composition strongly differed among species (or chemotypes). The floral scents of four of the investigated species (P. appendiculatum, P. cordatum, P. crassinervium, and P. eximium) and one of the two chemotypes of P. corcovadense were dominated by (Z)-jasmone (46 to 100% total relative concentration). High relative amounts of (Z)-2-pentenyl acetate (44 to 66%) characterized the samples of P. undulatum and Philodendron bipinnatifidum, while (E)-4,8-dimethyl-1,3,7-nonatriene was the main constituent in samples of P. curvilobium (75%) and the other P. corcovadense chemotype (56%). The scents of Philodendron spp. pollinated by C. variolosa differed from those of conspecifics associated with other cyclocephaline beetle species, but we also verified significant interspecific variation among these species sharing a common pollinator. We hypothesize that this community of co-flowering plants might be reproductively isolated despite being pollinated by the same pollinator species and having partly overlapping scent compositions.