Evolution and diversity of floral scent chemistry in the euglossine bee-pollinated orchid genus Gongora

• Published in: Annals of botany 2016-07, Vol.118 (1), p.135-148
• Main Authors: Hetherington-Rauth, Molly C., Ramírez, Santiago R.
• Format: Article
• Language: English
• Subjects: Animals; Bees; Biodiversity; Biological Evolution; Colombia; Costa Rica; Flowers - chemistry; Flowers - physiology; Gas Chromatography-Mass Spectrometry; Odorants - analysis; Orchid Biology; Orchidaceae - chemistry; Orchidaceae - physiology; PART OF A HIGHLIGHT ON ORCHID BIOLOGY; Pollination; Species Specificity; Volatile Organic Compounds - analysis
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mcw072

• Animal-pollinated angiosperms have evolved a variety of signalling mechanisms to attract pollinators. Floral scent is a key component of pollinator attraction, and its chemistry modulates both pollinator behaviour and the formation of plant-pollinator networks. The neotropical orchid genus Gongora exhibits specialized pollinator associations with male orchid bees (Euglossini). Male bees visit orchid flowers to collect volatile chemical compounds that they store in hind-leg pouches to use subsequently during courtship display. Hence, Gongora floral scent compounds simultaneously serve as signalling molecules and pollinator rewards. Furthermore, because floral scent acts as the predominant reproductive isolating barrier among lineages, it has been hypothesized that chemical traits are highly species specific. A comparative analysis of intra- and inter-specific variation of floral scent chemistry was conducted to investigate the evolutionary patterns across the genus. • Gas chromatography-mass spectrometry (GC-MS) was used to analyse the floral scent of 78 individuals belonging to 28 different species of Gongora from two of the three major lineages sampled across the neotropical region. Multidimensional scaling and indicator value analyses were implemented to investigate the patterns of chemical diversity within and among taxonomic groups at various geographic scales. Additionally, pollinator observations were conducted on a sympatric community of Gongora orchids exhibiting distinct floral scent phenotypes. • A total of 83 floral volatiles, mainly terpenes and aromatic compounds, were detected. Many of the identified compounds are common across diverse angiosperm families (e.g. cineole, eugenol, β-ocimene, β-pinene and terpinen-4-ol), while others are relatively rare outside euglossine bee-pollinated orchid lineages. Additionally, 29 volatiles were identified that are known to attract and elicit collection behaviour in male bees. Floral scent traits were less variable within species than between species, and the analysis revealed exceptional levels of cryptic diversity. Gongora species were divided into 15 fragrance groups based on shared compounds. Fragrance groups indicate that floral scent variation is not predicted by taxonomic rank or biogeographic region. • Gongora orchids emit a diverse array of scent molecules that are largely species specific, and closely related taxa exhibit qualitatively and quantitatively divergent chemical profiles. It is shown