Metamorphosing insects pay weapon growth costs that vertebrates avoid.

Evidence

Trade-offs among developing structures are widespread in insects, and they constitute a dramatic cost of growing elaborate weapons. But this particular cost—stunted growth of other structures—applies primarily to insects such as beetles, flies, ants, and bees. It does not apply to any animals that I am aware of outside of insects. The reason almost certainly has to do with the way these particular insects develop. Specifically, it has to do with when, during development, all of the various adult structures are formed. Exaggerated weapons of sexual selection always grow at the end of development, around the time when males reach sexual maturity. Deer, elk, and moose all begin antler growth only after males are young adults. Elephants and boars grow their tusks after they are adults. Even shrimp and crabs begin the process of enlargement of their fighting claws around the time that their gonads mature. In all of these animals, bodies have already grown and organs, tissues, and appendages are already at or near their adult proportions, long before the weapons begin to grow. Weapons cannot stunt the growth of other traits in these animals because all of the other structures are produced first. In contrast, beetles, bees, flies, and ants all undergo metamorphosis as they develop, and this means that they grow their adult body parts at the same time as their weapons. Simultaneous growth exposes these structures to the insidious effects of resource limitation and allocation trade-offs. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 758

Categorization

• DEFINE: Explains why the weapon growth trade-off is limited to insects: metamorphosis forces simultaneous growth of weapons and other structures.
• XREF: Connects to the book’s broader thesis about evolutionary costs of weapon elaboration, and the mammal/vertebrate examples (deer, elephants, boars, shrimp) contrast with insects.
• corroborated: 2 independent passages support this claim — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 758

Related

• Weapons grow late because development prioritizes mandatory survival expenses first (similarity 0.83)
• Weapons in arms races get so big they impair other bodily functions (similarity 0.83)
• Arms-race weapon growth makes resource trade-offs drastically impair body functions (similarity 0.82)
• Extreme weapons across many insect species stunt eyes, wings, antennae, and testes (similarity 0.82)
• Weapons evolve only when reproductive benefits exceed costs (similarity 0.81)
• Weapon growth is far more resource-sensitive than other body parts (similarity 0.81)
• Growing large weapons diverts resources and stunts other body parts (similarity 0.81)
• Releasing soldiers from other tasks lets weapons evolve to extremes (similarity 0.80)
• Weapon growth widens the gap between the best- and worst-armed males. (similarity 0.79)
• Human armies and social insects solved the same weapon trade-off by role specialization (similarity 0.79)
• Competition for reproduction drives evolution of nature’s biggest weapons (similarity 0.79)
• The evolutionary drivers of animal weapons also explain human weapon elaboration. (similarity 0.79)
• Variation in animal weapon size is explainable by species ecology and behavior. (similarity 0.79)
• Climate-driven food decline may have tipped costly antler growth toward extinction (similarity 0.79)
• Animal weapons can evolve rapidly within just seven generations (similarity 0.79)