title: Morphological and Transcriptomic Analysis of a Beetle Chemosensory System Reveals a Gnathal Olfactory Center.
abstract: The red flour beetle Tribolium castaneum is an emerging insect model organism representing the largest insect order, Coleoptera, which encompasses several serious agricultural and forest pests. Despite the ecological and economic importance of beetles, most insect olfaction studies have so far focused on dipteran, lepidopteran, or hymenopteran systems.
  
  
  
  Here, we present the first detailed morphological description of a coleopteran olfactory pathway in combination with genome-wide expression analysis of the relevant gene families involved in chemoreception. Our study revealed that besides the antennae, also the mouthparts are highly involved in olfaction and that their respective contribution is processed separately. In this beetle, olfactory sensory neurons from the mouthparts project to the lobus glomerulatus, a structure so far only characterized in hemimetabolous insects, as well as to a so far non-described unpaired glomerularly organized olfactory neuropil in the gnathal ganglion, which we term the gnathal olfactory center. The high number of functional odorant receptor genes expressed in the mouthparts also supports the importance of the maxillary and labial palps in olfaction of this beetle. Moreover, gustatory perception seems equally distributed between antenna and mouthparts, since the number of expressed gustatory receptors is similar for both organs.
  
  
  
  Our analysis of the T. castaneum chemosensory system confirms that olfactory and gustatory perception are not organotopically separated to the antennae and mouthparts, respectively. The identification of additional olfactory processing centers, the lobus glomerulatus and the gnathal olfactory center, is in contrast to the current picture that in holometabolous insects all olfactory inputs allegedly converge in the antennal lobe. These findings indicate that Holometabola have evolved a wider variety of solutions to chemoreception than previously assumed.
authors.affiliation: Department of Developmental Biology, Göttingen Center for Molecular Biosciences (GZMB), Georg-August-University Goettingen, Johann-Friedrich-Blumenbach-Institute of Zoology and Anthropology, Ernst-Caspari-Haus, Justus-von-Liebig-Weg 11, 37077, Göttingen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Dippel
authors.affiliation: Department of Biology - Neurobiology/Ethology, Philipps-University Marburg, Karl-von-Frisch-Str. 8, 35032, Marburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Kollmann
authors.affiliation: Department of Evolutionary Developmental Genetics, GZMB, Ernst-Caspari-Haus, Georg-August-University Goettingen, Johann-Friedrich-Blumenbach-Institute of Zoology and Anthropology, Justus-von-Liebig-Weg 11, 37077, Göttingen, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Oberhofer
authors.affiliation: Department of Developmental Biology, Göttingen Center for Molecular Biosciences (GZMB), Georg-August-University Goettingen, Johann-Friedrich-Blumenbach-Institute of Zoology and Anthropology, Ernst-Caspari-Haus, Justus-von-Liebig-Weg 11, 37077, Göttingen, Germany.
authors.forename: Alice
authors.initials: A
authors.lastname: Montino
authors.affiliation: Department of Biology - Neurobiology/Ethology, Philipps-University Marburg, Karl-von-Frisch-Str. 8, 35032, Marburg, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Knoll
authors.affiliation: Department of Biology - Neurobiology/Ethology, Philipps-University Marburg, Karl-von-Frisch-Str. 8, 35032, Marburg, Germany.
authors.forename: Milosz
authors.initials: M
authors.lastname: Krala
authors.affiliation: Department of Biology - Mycology, Philipps-University Marburg, Karl-von-Frisch-Str. 8, 35032, Marburg, Germany.
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Rexer
authors.affiliation: Department of Biology - Neurobiology/Ethology, Philipps-University Marburg, Karl-von-Frisch-Str. 8, 35032, Marburg, Germany.
authors.forename: Sergius
authors.initials: S
authors.lastname: Frank
authors.affiliation: Department of Plant Systems Biology, Flanders Institute for Biotechnology, Technologiepark 927, 9052, Gent, Belgium.
authors.forename: Robert
authors.initials: R
authors.lastname: Kumpf
authors.affiliation: Department of Biology - Neurobiology/Ethology, Philipps-University Marburg, Karl-von-Frisch-Str. 8, 35032, Marburg, Germany. joachim.schachtner@biologie.uni-marburg.de.
authors.forename: Joachim
authors.initials: J
authors.lastname: Schachtner
authors.affiliation: Department of Developmental Biology, Göttingen Center for Molecular Biosciences (GZMB), Georg-August-University Goettingen, Johann-Friedrich-Blumenbach-Institute of Zoology and Anthropology, Ernst-Caspari-Haus, Justus-von-Liebig-Weg 11, 37077, Göttingen, Germany. ewimmer@gwdg.de.
authors.forename: Ernst A
authors.initials: EA
authors.lastname: Wimmer
mesh_terms: D000818:Animals; D002628:Chemoreceptor Cells / Q000378:metabolism; D001517:Coleoptera / Q000235:genetics* / Q000378:metabolism; D020869:Gene Expression Profiling / Q000379:methods*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D018034:Olfactory Receptor Neurons / Q000378:metabolism; D018035:Receptors, Odorant / Q000235:genetics / Q000378:metabolism
chemical_list: D019476:Insect Proteins; D018035:Receptors, Odorant
keywords: Tribolium castaneum; chemoreception; gustation; insect; lobus glomerulatus; neuroanatomy; olfaction