Development and function of perfume signals in orchid bees

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Chemical signals are used in the mating behavior of many arthropods, especially insects, exhibiting a large variability in chemical complexityand substance classes. Possible functions range from mediating mate/species recognition (recognition function) to signaling status and competitive strength in male-male interactions (armament function) to signaling genetic fitness to choosy mates (ornament function). All three functions may be non-exclusive co-options of the same trait as it is displayed in different contexts and to different receivers. In the present project we will evaluate these functions in an enigmatic chemical signaling trait, the environment-derived ‘perfume’ of male neotropical orchid bees (Euglossini). We will carry out a combination of field and cage experiments using newly developed techniques for (1) monitoring individual male perfume development and (2) for testing perfume effects on sexual display and mating behavior. With regard to (2) we will extrapolate from our recent success in enabling the complete orchid bee (Euglossa dilemma) reproductive behavior in flight cages. As a central part of the project, we will present virgin females with dual choices of males whose perfume loads we have manipulated: with and without perfume (perfume possession experiment), the amount of perfume (perfume intensity experiment), the species-correctness of the perfume (specificity experiment), and the presence of a certain major compound that is likely to mediate perfume specificity (HNDB experiment). The results of these experiments, plus the analysis of perfume-dependence of male-male interactions, will allow us to evaluate the importance of recognition, armament, and ornament functions in shaping the evolution of euglossine perfumes, and will help us to further establish orchid bees as a model system for the study of mating behavior, sexual selection, and speciation.