Beetle horns can be impressively large yet nearly cost-free to produce and use

Evidence

As I was writing this book, a doctoral student in my lab, Erin McCullough, was systematically unraveling this notion for the rhinoceros beetle we study. Her work shook the field, because everyone—including myself—assumed that the giant pitchfork horns in these beetles were costly. How could they not be? These weapons are two-thirds the length of the beetle, and they splay forward in front of the animal’s face like a massive pitchfork. Yet, these horns turned out to be remarkably inexpensive to produce, and virtually cost-free to fly around with. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 810

Categorization

• XREF: Reverses the common ‘costly signaling’ assumption in animal weaponry; connects to the broader weapons-evolution cost framework in earlier chapters. — connects to: Beetle horns can reach 30 percent of male body weight — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 192; Scarcity of egg-laying sites made big beetle weapons enormously beneficial — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 211

Related

• Beetle horns can reach 30 percent of male body weight (similarity 0.90)
• Extreme weapons across many insect species stunt eyes, wings, antennae, and testes (similarity 0.84)
• Scarcity of egg-laying sites made big beetle weapons enormously beneficial (similarity 0.83)
• Weapon growth is far more resource-sensitive than other body parts (similarity 0.82)
• Horn growth is nine times more nutrition-sensitive than genitalia in beetles (similarity 0.82)
• Weapons evolve only when reproductive benefits exceed costs (similarity 0.81)
• Competition for reproduction drives evolution of nature’s biggest weapons (similarity 0.81)
• Variation in animal weapon size is explainable by species ecology and behavior. (similarity 0.81)
• Bigger weapons usually fail because their costs outweigh their benefits (similarity 0.81)
• Mobile resources deny weapons a cost-effective performance advantage (similarity 0.81)
• Dung beetles offer the ideal study system for extreme weapon evolution. (similarity 0.80)
• Natural selection usually favors modest weapon size because cost offsets benefit (similarity 0.80)
• Growing large weapons diverts resources and stunts other body parts (similarity 0.80)
• Weapon size in animal species is under stabilizing selection, not open-ended directional selection (similarity 0.79)
• Weapons in arms races get so big they impair other bodily functions (similarity 0.79)

Broader Connections

• Beetle horns can reach 30 percent of male body weight #expands (0.85) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 192
• Scarcity of egg-laying sites made big beetle weapons enormously beneficial #corroborates (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 211