Intraspecific Geographic Variation of Fragrances Acquiredby Orchid Bees in Native and Introduced Populations

Abstract

Male orchid bees collect volatiles, from bothfloral and non-floral sources, that they expose as phero-mone analogues (perfumes) during courtship display. Thechemical profile of these perfumes, which includes terpenesand aromatic compounds, is both species-specific anddivergent among closely related lineages. Thus, fragrancecomposition is thought to play an important role inprezygotic reproductive isolation in euglossine bees. How-ever, because orchid bees acquire fragrances entirely fromexogenous sources, the chemical composition of maleperfumes is prone to variation due to environmentalheterogeneity across habitats. We used Gas Chromatog-raphy/Mass Spectrometry (GC/MS) to characterize theperfumes of 114 individuals of the green orchid bee(Euglossaaff.viridissima) sampled from five nativepopulations in Mesoamerica and two naturalized popula-tions in the southeastern United States. We recorded a totalof 292 fragrance compounds from hind-leg extracts, andfound that overall perfume composition was different foreach population. We detected a pronounced chemicaldissimilarity between native (Mesoamerica) and naturalized(U.S.) populations that was driven both by proportionaldifferences of common compounds as well as the presenceof a few chemicals unique to each population group. Despitethese differences, our data also revealed remarkable qualita-tive consistency in the presence of several major fragrancecompounds across distant populations from dissimilar hab-itats. In addition, we demonstrate that naturalized bees areattracted to and collect large quantities of triclopyr 2-butoxyethyl ester, the active ingredient of several commer-cially available herbicides. By comparing incidence valuesand consistency indices across populations, we identifyputative functional compounds that may play an importantrole in courtship signaling in this species of orchid bee