title: Rapid evolution of chemosensory receptor genes in a pair of sibling species of orchid bees (Apidae: Euglossini).
abstract: BACKGROUND
  Insects rely more on chemical signals (semiochemicals) than on any other sensory modality to find, identify, and choose mates. In most insects, pheromone production is typically regulated through biosynthetic pathways, whereas pheromone sensory detection is controlled by the olfactory system. Orchid bees are exceptional in that their semiochemicals are not produced metabolically, but instead male bees collect odoriferous compounds (perfumes) from the environment and store them in specialized hind-leg pockets to subsequently expose during courtship display. Thus, the olfactory sensory system of orchid bees simultaneously controls male perfume traits (sender components) and female preferences (receiver components). This functional linkage increases the opportunities for parallel evolution of male traits and female preferences, particularly in response to genetic changes of chemosensory detection (e.g. Odorant Receptor genes). To identify whether shifts in pheromone composition among related lineages of orchid bees are associated with divergence in chemosensory genes of the olfactory periphery, we searched for patterns of divergent selection across the antennal transcriptomes of two recently diverged sibling species Euglossa dilemma and E. viridissima.
  
  
  RESULTS
  We identified 3185 orthologous genes including 94 chemosensory loci from five different gene families (Odorant Receptors, Ionotropic Receptors, Gustatory Receptors, Odorant Binding Proteins, and Chemosensory Proteins). Our results revealed that orthologs with signatures of divergent selection between E. dilemma and E. viridissima were significantly enriched for chemosensory genes. Notably, elevated signals of divergent selection were almost exclusively observed among chemosensory receptors (i.e. Odorant Receptors).
  
  
  CONCLUSIONS
  Our results suggest that rapid changes in the chemosensory gene family occurred among closely related species of orchid bees. These findings are consistent with the hypothesis that strong divergent selection acting on chemosensory receptor genes plays an important role in the evolution and diversification of insect pheromone systems.
authors: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitätsstrasse 150, D-44801, Bochum, Germany. pbrand@ucdavis.edu.|Department for Evolution and Ecology, Center for Population Biology, University of California Davis, One Shields Avenue, 95616, Davis, USA. pbrand@ucdavis.edu.
authors: Philipp
authors: P
authors: Brand
authors: Department for Evolution and Ecology, Center for Population Biology, University of California Davis, One Shields Avenue, 95616, Davis, USA. sanram@ucdavis.edu.
authors: Santiago R
authors: SR
authors: Ramírez
authors: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitätsstrasse 150, D-44801, Bochum, Germany. florian.leese@uni-due.de.|Present address: Faculty of Biology, Aquatic Ecosystems Research, University of Duisburg and Essen, Universitätsstrasse 5, D-45141, Essen, Germany. florian.leese@uni-due.de.
authors: Florian
authors: F
authors: Leese
authors: Departamento de Apicultura, Universidad Autónoma de Yucatán, Mérida, Mexico. javier.quezada@correo.uady.mx.
authors: J Javier G
authors: JJ
authors: Quezada-Euan
authors: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitätsstrasse 150, D-44801, Bochum, Germany. tollrian@rub.de.
authors: Ralph
authors: R
authors: Tollrian
authors: Department of Animal Ecology, Evolution and Biodiversity, Ruhr University Bochum, Universitätsstrasse 150, D-44801, Bochum, Germany. thomas.eltz@rub.de.
authors: Thomas
authors: T
authors: Eltz
mesh_terms: D000818:Animals; D001516:Bees / Q000145:classification / Q000235:genetics* / Q000502:physiology; D019143:Evolution, Molecular; D005260:Female; D019476:Insect Proteins / Q000235:genetics*; D008297:Male; D010675:Pheromones / Q000378:metabolism; D010802:Phylogeny; D018035:Receptors, Odorant / Q000235:genetics*; D012903:Smell
chemical_list: D019476:Insect Proteins; D010675:Pheromones; D018035:Receptors, Odorant