title: Hedgehog signaling enables nutrition-responsive inhibition of an alternative morph in a polyphenic beetle.
abstract: The recruitment of modular developmental genetic components into new developmental contexts has been proposed as a central mechanism enabling the origin of novel traits and trait functions without necessitating the origin of novel pathways. Here, we investigate the function of the hedgehog (Hh) signaling pathway, a highly conserved pathway best understood for its role in patterning anterior/posterior (A/P) polarity of diverse traits, in the developmental evolution of beetle horns, an evolutionary novelty, and horn polyphenisms, a highly derived form of environment-responsive trait induction. We show that interactions among pathway members are conserved during development of Onthophagus horned beetles and have retained the ability to regulate A/P polarity in traditional appendages, such as legs. At the same time, the Hh signaling pathway has acquired a novel and highly unusual role in the nutrition-dependent regulation of horn polyphenisms by actively suppressing horn formation in low-nutrition males. Down-regulation of Hh signaling lifts this inhibition and returns a highly derived sigmoid horn body size allometry to its presumed ancestral, linear state. Our results suggest that recruitment of the Hh signaling pathway may have been a key step in the evolution of trait thresholds, such as those involved in horn polyphenisms and the corresponding origin of alternative phenotypes and complex allometries.
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405; Division of Plant and Soil Sciences, West Virginia University, Morgantown, WV 26506 tekijimoto@mail.wvu.edu.
authors.forename: Teiya
authors.initials: T
authors.lastname: Kijimoto
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405;
authors.forename: Armin P
authors.initials: AP
authors.lastname: Moczek
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000825:Animal Structures / Q000378:metabolism; D000818:Animals; D001517:Coleoptera / Q000235:genetics / Q000378:metabolism*; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D053823:Hedgehog Proteins; D019476:Insect Proteins
keywords: allometry; co-option; developmental plasticity; modularity; threshold trait