RESEARCH ARTICLE elifesciences.org Evolution of insect olfactory receptors Christine Missbach1*, Hany KM Dweck1, Heiko Vogel2, Andreas Vilcinskas3, Marcus C Stensmyr4, Bill S Hansson1†, Ewald Grosse-Wilde1*† 1Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology, Jena, Germany; 2Department of Entomology, Max Planck Institute for Chemical Ecology, Jena, Germany; 3Institute of Phytopathology and Applied Zoology, Justus-Liebig-Universität Gießen, Gießen, Germany; 4Department of Biology, Lund University, Lund, Sweden Abstract The olfactory sense detects a plethora of behaviorally relevant odor molecules; gene families involved in olfaction exhibit high diversity in different animal phyla. Insects detect volatile molecules using olfactory (OR) or ionotropic receptors (IR) and in some cases gustatory receptors (GRs). While IRs are expressed in olfactory organs across Protostomia, ORs have been hypothesized to be an adaptation to a terrestrial insect lifestyle. We investigated the olfactory system of the primary wingless bristletail Lepismachilis y-signata (Archaeognatha), the firebratThermobia domestica (Zygentoma) and the neopteran leaf insect Phyllium siccifolium (Phasmatodea). ORs and the olfactory coreceptor (Orco) are with very high probability lacking in Lepismachilis; in Thermobia we have identified three Orco candidates, and in Phyllium a fully developed OR/Orco-based system. We suggest that ORs did not arise as an adaptation to a terrestrial lifestyle, but evolved later in insect evolution, with Orco being present before the appearance of ORs. DOI: 10.7554/eLife.02115.001 *For correspondence:
[email protected] (CM);
[email protected] (EG-W) Introduction †These authors contributed All living organisms, including bacteria, protozoans, fungi, plants, and animals, detect chemicals in equally to this work as senior their environment.