title: Olfactory specialization for perfume collection in male orchid bees.
abstract: Insects rely on the olfactory system to detect a vast diversity of airborne molecules in their environment. Highly sensitive olfactory tuning is expected to evolve when detection of a particular chemical with great precision is required in the context of foraging and/or finding mates. Male neotropical orchid bees (Euglossini) collect odoriferous substances from multiple sources, store them in specialized tibial pouches and later expose them at display sites, presumably as mating signals to females. Previous analysis of tibial compounds among sympatric species revealed substantial chemical disparity in chemical composition among lineages with outstanding divergence between closely related species. Here, we tested whether specific perfume phenotypes coevolve with matching olfactory adaptations in male orchid bees to facilitate the location and harvest of species-specific perfume compounds. We conducted electroantennographic (EAG) measurements on males of 15 sympatric species in the genus Euglossa that were stimulated with 18 compounds present in variable proportions in male hind tibiae. Antennal response profiles were species-specific across all 15 species, but there was no conspicuous differentiation between closely related species. Instead, we found that the observed variation in EAG activity follows a Brownian motion model of trait evolution, where the probability of differentiation increases proportionally with lineage divergence time. However, we identified strong antennal responses for some chemicals that are present as major compounds in the perfume of the same species, thus suggesting that sensory specialization has occurred within multiple lineages. This sensory specialization was particularly apparent for semi-volatile molecules ('base note' compounds), thus supporting the idea that such compounds play an important role in chemical signaling of euglossine bees. Overall, our study found no close correspondence between antennal responses and behavioral preferences/tibial contents, but confirms the utility of EAG profiling for discovering certain behaviorally active compounds.
authors.affiliation: Department of Animal Ecology, Evolution and Biodiversity, Ruhr-Universität Bochum, Bochum 44780, Germany.
authors.forename: Lukasz
authors.initials: L
authors.lastname: Mitko
authors.affiliation: The Center for Population Biology, University of California, Davis, Davis, CA 95616, USA.
authors.forename: Marjorie G
authors.initials: MG
authors.lastname: Weber
authors.affiliation: Department of Evolution and Ecology, University of California, Davis, CA 95616, USA.
authors.forename: Santiago R
authors.initials: SR
authors.lastname: Ramirez
authors.affiliation: Chemistry, Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, Sundsvall SE-851 70, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Hedenström
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors.forename: William T
authors.initials: WT
authors.lastname: Wcislo
authors.affiliation: Department of Animal Ecology, Evolution and Biodiversity, Ruhr-Universität Bochum, Bochum 44780, Germany thomas.eltz@ruhr-uni-bochum.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Eltz
mesh_terms: D000818:Animals; D057506:Arthropod Antennae / Q000502:physiology; D001516:Bees / Q000502:physiology*; D008297:Male; D029595:Orchidaceae / Q000469:parasitology*; D010476:Perfume / Q000032:analysis*; D012111:Residence Characteristics; D012903:Smell / Q000502:physiology*; D012997:Solvents; D013045:Species Specificity
chemical_list: D010476:Perfume; D012997:Solvents
keywords: EAG; Euglossini; Fragrance; Olfaction; Olfactory specialization; Pheromone