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Coming apart at the seams: morphological evidence for pregnathal head capsule borders in adult Tribolium castaneum

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Cephalization and seamless fusion of the anterior body segments during development obscure the segmental boundaries of the insect head. Most of the visible seams are thought to reflect cuticular infolding for structural reinforcement rather than a merger of cuticular plate borders. Incomplete fusions and other modifications of the adult head found in eight Tribolium mutations indicate that the frontal and gular sutures likely are true sutures that mark borders between adjacent cuticular plates, and suggest that the anterior facial shelf is a composite of three independent cuticular surfaces: ocular, antennal, and clypeo-labral. Additionally, midline splits of the clypeo-labrum and gula, and membranous lesions on the lateral head capsule reveal probable borders of adjacent cuticular plates where visible sutures are normally absent. The anterior lateral lesions seen in the Lucifer mutation mark a border between ocular and antennal plates and appear to identify part of the postfrontal sutures. While revealing or clarifying possible intersegmental borders between ocular, antennal, and clypeo-labral plates, the various modified or unfused surfaces of the head neither reveal an additional acronal plate nor support the view that the clypeo-labrum is segmentally associated with ocular cuticle.

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We thank Bruce Heming, Urs Schmidt-Ott and an anonymous reviewer for helpful comments on the manuscript, and Kathy Leonard and Sue Brown for discovering and providing the Tlr mutant. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.

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Correspondence to Richard W. Beeman.

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Communicated by S. Roth

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Haas, M.S., Beeman, R.W. Coming apart at the seams: morphological evidence for pregnathal head capsule borders in adult Tribolium castaneum . Dev Genes Evol 222, 99–111 (2012). https://doi.org/10.1007/s00427-012-0397-5

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  • Tribolium castaneum
  • Head development
  • Procephalon
  • Suture
  • Labrum
  • Acron