title: The function of appendage patterning genes in mandible development of the sexually dimorphic stag beetle.
abstract: One of the defining features of the evolutionary success of insects is the morphological diversification of their appendages, especially mouthparts. Although most insects share a common mouthpart ground plan, there is remarkable diversity in the relative size and shapes of these appendages among different insect lineages. One of the most prominent examples of mouthpart modification can be found in the enlargement of mandibles in stag beetles (Coleoptera, Insecta). In order to understand the proximate mechanisms of mouthpart modification, we investigated the function of appendage-patterning genes in mandibular enlargement during extreme growth of the sexually dimorphic mandibles of the stag beetle Cyclommatus metallifer. Based on knowledge from Drosophila and Tribolium studies, we focused on seven appendage patterning genes (Distal-less (Dll), aristaless (al), dachshund (dac), homothorax (hth), Epidermal growth factor receptor (Egfr), escargot (esg), and Keren (Krn). In order to characterize the developmental function of these genes, we performed functional analyses by using RNA interference (RNAi). Importantly, we found that RNAi knockdown of dac resulted in a significant mandible size reduction in males but not in female mandibles. In addition to reducing the size of mandibles, dac knockdown also resulted in a loss of the serrate teeth structures on the mandibles of males and females. We found that al and hth play a significant role during morphogenesis of the large male-specific inner mandibular tooth. On the other hand, knockdown of the distal selector gene Dll did not affect mandible development, supporting the hypothesis that mandibles likely do not contain the distal-most region of the ancestral appendage and therefore co-option of Dll expression is unlikely to be involved in mandible enlargement in stag beetles. In addition to mandible development, we explored possible roles of these genes in controlling the divergent antennal morphology of Coleoptera.
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan; Department of Entomology, Washington State University, Pullman, WA 99164, USA; Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan. Electronic address: h-r-goto@ees.hokudai.ac.jp.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Gotoh
authors.affiliation: Department of Entomology, Washington State University, Pullman, WA 99164, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Zinna
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan; Graduate School of Sciences, Nagoya University, Nagoya, Aichi 464-8601, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ishikawa
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan; Faculty of Agriculture, Utsunomiya University, Utsunomiya, Tochigi 321-8505, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Miyakawa
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan; Division of Ecological Genetics, Department of Population Genetics, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan.
authors.forename: Asano
authors.initials: A
authors.lastname: Ishikawa
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Sugime
authors.affiliation: Division of Biological Sciences, University of Montana-Missoula, MT 59812, USA.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Emlen
authors.affiliation: Department of Entomology, Washington State University, Pullman, WA 99164, USA.
authors.forename: Laura C
authors.initials: LC
authors.lastname: Lavine
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Miura
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics*; D001517:Coleoptera / Q000196:embryology*; D066246:ErbB Receptors / Q000502:physiology; D005260:Female; D019476:Insect Proteins / Q000235:genetics / Q000502:physiology; D008297:Male; D008334:Mandible / Q000196:embryology*; D012727:Sex Characteristics; D019849:Sex Determination Processes
chemical_list: D019476:Insect Proteins; D066246:ErbB Receptors
keywords: Appendage patterning; Exaggerated trait; RNAi; Sexual dimorphism; Stag beetle