A Mechanism of Extreme Growth and Reliable Signaling in Sexually Selected Ornaments and Weapons

• Published in: Science (American Association for the Advancement of Science) Vol. 337; no. 6096; pp. 860 - 864
• Main Authors: Emlen, Douglas J., Warren, Ian A., Johns, Annika, Dworkin, Ian, Lavine, Laura Corley
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 17.08.2012; The American Association for the Advancement of Science
• Subjects: Animal wings; Animals; Beetles; Biological and medical sciences; Biological evolution; Body size; Cell growth; Coleoptera - anatomy & histology; Coleoptera - genetics; Coleoptera - growth & development; Deer; Evolution; Fitness; Fundamental and applied biological sciences. Psychology; Gene Knockdown Techniques; Genetics of eukaryotes. Biological and molecular evolution; Genitalia; Growth traits; Horns; Horns - anatomy & histology; Horns - growth & development; Insulin - physiology; Insulin-like growth factors; Male; Male animals; Mating Preference, Animal; Molecular Sequence Data; Online; Pathways; Phenotypic traits; Receptor, Insulin - genetics; Receptor, Insulin - physiology; Sexual selection; Signal Transduction; Somatomedins - physiology; Weapons; Insulin like growth factor; Vertebrata; Secondary sexual character; Sexual selection; Biological evolution; Morphology; Male; Invertebrata; Mechanism of action
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1224286

Many male animals wield ornaments or weapons of exaggerated proportions. We propose that increased cellular sensitivity to signaling through the insulin/insulin-like growth factor (IGF) pathway may be responsible for the extreme growth of these structures. We document how rhinoceros beetle horns, a sexually selected weapon, are more sensitive to nutrition and more responsive to perturbation of the insulin/IGF pathway than other body structures. We then illustrate how enhanced sensitivity to insulin/IGF signaling in a growing ornament or weapon would cause heightened condition sensitivity and increased variability in expression among individuals—critical properties of reliable signals of male quality. The possibility that reliable signaling arises as a by-product of the growth mechanism may explain why trait exaggeration has evolved so many different times in the context of sexual selection.