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Open AccessArticle

Variation in an Extreme Weapon: Horn Performance Differences across Rhinoceros Beetle (Trypoxylus dichotomus) Populations

1
Biology Department, Gonzaga University, Spokane, WA 99258, USA
2
Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
3
Department of Entomology, Washington State University, Pullman, WA 99164, USA
*
Author to whom correspondence should be addressed.
Insects 2019, 10(10), 346; https://doi.org/10.3390/insects10100346
Received: 24 September 2019 / Revised: 1 October 2019 / Accepted: 3 October 2019 / Published: 15 October 2019
Japanese rhinoceros beetle (Trypoxylus dichotomus) males have exaggerated head horns that they use as weapons in combat over reproductive opportunities. In these contests, there is an advantage to having a longer horn, and there seems to be little cost to horn exaggeration. However, populations vary in the amount of horn exaggeration across this widespread species. Here, we examine four populations and quantify scaling and functional morphology of the horn. We then measure force production by the horn system in a combat-relevant movement. We find that not only does horn length vary among populations, but allometry of lever mechanics and force production varies in a complex way. For instance, some beetle populations make relatively long horns, but exert relatively low forces. Other populations make shorter horns and produce higher forces during fights. We suggest that this performance variation could be associated with differences in the intensity or type of sexual selection across the species. View Full-Text
Keywords: allometry; sexual selection; force production; armament allometry; sexual selection; force production; armament
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Buchalski, B.; Gutierrez, E.; Emlen, D.; Lavine, L.; Swanson, B. Variation in an Extreme Weapon: Horn Performance Differences across Rhinoceros Beetle (Trypoxylus dichotomus) Populations. Insects 2019, 10, 346.

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