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Science 337 (6096): 860-864

Copyright © 2012 by the American Association for the Advancement of Science

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

Douglas J. Emlen,1,* Ian A. Warren,2 Annika Johns,1 Ian Dworkin,3 Laura Corley Lavine2

Abstract: 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.

1 Division of Biological Sciences, The University of Montana, 104 Health Science Building, Missoula, MT 59812, USA.
2 Department of Entomology, Washington State University, Pullman, WA 99164–6382, USA.
3 Department of Zoology, Michigan State University, East Lansing, MI 48824, USA.

* To whom correspondence should be addressed. E-mail: doug.emlen{at}mso.umt.edu

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