Chemical Profiles of Floral Structures in Nicotiana alata and N. forgetiana: Pollen and Corolla Volatiles in Parental Species and Natural Hybrid Corollas

Abstract

Nicotiana alata (hawkmoth-pollinated) and N. forgetiana (hummingbird-pollinated) are two closely related species that were considered reproductively isolated due to their divergent pollination systems. However, the discovery of a natural hybrid zone challenges this view. Floral volatile profiles of these species and their natural hybrids were characterized to identify possible mechanisms and consequences of unexpected gene flow. Organ-specific (corolla, pollen) and diel (day, night) volatile emissions were analyzed using HS-SPME-GC-MS. Corolla scents were dominated by oxygenated monoterpenoids, while pollen blends were rich in microbial-associated compounds, such as acetoin. Hybrid scent profiles more closely match their floral phenotype than their genomic ancestry, with intermediate hybrids emitting blends distinct from those of both parental species. The discovery of a natural hybrid zone, combined with phenotype-specific scent emissions, challenges the view of strict pollinator isolation. Floral scent presents a complex, modular trait that may facilitate hybridization in this system.