Males evolve big weapons to defend resources that females visit

Evidence

Males in many animals, such as these flies, fight over restricted, economically defensible resources visited by females. In these situations, big weapons are often beneficial. Above: Stalk-eyed flies defend hanging rootlets on which females roost. Below: Antlered flies defend egg-laying holes in the bark of fallen trees. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 960 (#corroborates, via linked claim)

In the animal world, extreme weapons are usually confined to specific, rare circumstances such as sit-and-wait hunting tactics, or within-colony division of labor. But another surprisingly potent phenomenon can lead to the evolution of exaggerated weapon sizes: competition. Nature’s biggest weapons decide the outcomes of battles over the chance to reproduce, the most precious commodity of all. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 136 (#expands, via linked claim)

Sexual selection differs from most forms of natural selection in ways tailor-made for pushing traits to their extreme. For one thing, sexual selection can be a lot stronger than natural selection. Whenever a small subset of males monopolizes access to large numbers of females, the disparity in reproductive success skyrockets. A few victorious males sire dozens or even hundreds of offspring, while the overwhelming majority of males sire none. When payoffs for success are high enough, weapons can evolve to really big sizes. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 177 (#expands, via linked claim)

Categorization

• XREF: connects to: Among jacanas, females are the armed, aggressive sex defending breeding territories.; Sexual selection drives weapons to extremes because payoffs for winners are enormous.; Reproductive success, not survival, drives the largest animal weapons (+11 more)

Related

• Weapon size is favored when males defend resources females need (similarity 0.97)
• Among jacanas, females are the armed, aggressive sex defending breeding territories. (similarity 0.93)
• In nearly all weaponed species, males carry the weapons, not females. (similarity 0.88)
• Reproductive success, not survival, drives the largest animal weapons (similarity 0.86)
• Competition for reproduction drives evolution of nature’s biggest weapons (similarity 0.85)
• Sexual selection drives weapons to extremes because payoffs for winners are enormous. (similarity 0.84)
• Sexual selection can be far stronger than natural selection and drives weapon extremes (similarity 0.84)
• Extreme male weapons evolved independently at least eleven times in vinegar flies (similarity 0.84)
• Male parental care can invert the direction of sexual selection and weaponry (similarity 0.83)
• Weapon evolution needs both competition and economically defensible resources (similarity 0.83)
• Weapons evolve only when reproductive benefits exceed costs (similarity 0.82)
• Scarcity of egg-laying sites made big beetle weapons enormously beneficial (similarity 0.82)
• Rare localized resources translate fighting success into reproductive success (similarity 0.82)
• Scarcity of suitable feeding sites drives weapon evolution in harlequin beetles (similarity 0.81)
• Weapon size in animal species is under stabilizing selection, not open-ended directional selection (similarity 0.81)

Broader Connections

• Weapon size is favored when males defend resources females need #corroborates (1.00) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 960
• Competition for reproduction drives evolution of nature’s biggest weapons #expands (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 136
• Sexual selection can be far stronger than natural selection and drives weapon extremes #expands (0.60) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 177