The olfactory component of floral display in Asimina and Deeringothamnus (Annonaceae)

Floral scent is a key component of floral display, and probably one of the first floral attractants linking insect pollinators to the radiation of Angiosperms. In this article, we investigate floral scent in two extra-tropical genera of Annonaceae. We discuss floral scent in the context of differing pollination strategies in these genera, and compare their scent to that of a close tropical relative. Floral volatiles were collected for Annona glabra, Asimina and Deeringothamnus whole flowers and dissected floral organs, using a standardized static-headspace solid phase microextraction method. Scents were analyzed using gas chromatography-mass spectrometry, and identified using known standards. The floral scents of these species are highly dynamic, varying between floral organs, sexual stages and species. Maroon-flowered species of Asimina produce 'yeasty' odors, dominated by fermentation volatiles and occasionally containing sulfurous or nitrogenous compounds. White-flowered species of Asimina and Deeringothamnus produce pleasant odors characterized by lilac compounds, benzenoids and hydrocarbons. Annona glabra produces a strong, fruity-acetonic scent dominated by 3-pentanyl acetate and 1,8-cineole. The fermented/decaying scents of maroon-flowered species of Asimina suggest mimicry-based pollination strategies similar to aroids and stapeliads, whereas the pleasant scents of white-flowered species of Asimina suggest honest, reward-based pollination strategies. The scent of Annona glabra is typical of specialized beetle pollination systems common to tropical Annonaceae.