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Summary: On the origin and evolutionary diversification
of beetle horns
Douglas J. Emlen*
, Laura Corley Lavine
, and Ben Ewen-Campen*
*Division of Biological Sciences, University of Montana, Missoula, MT 59812; and Department of Entomology, Washington State University,
Pullman, WA 99164
Many scarab beetles produce rigid projections from the body called
horns. The exaggerated sizes of these structures and the stagger-
ing diversity of their forms have impressed biologists for centuries.
Recent comparative studies using DNA sequence-based phylog-
enies have begun to reconstruct the historical patterns of beetle
horn evolution. At the same time, developmental genetic experi-
ments have begun to elucidate how beetle horns grow and how
horn growth is modulated in response to environmental variables,
such as nutrition. We bring together these two perspectives to
show that they converge on very similar conclusions regarding
beetle evolution. Horns do not appear to be difficult structures to
gain or lose, and they can diverge both dramatically and rapidly in
form. Although much of this work is still preliminary, we use
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