Digest: Sexually selected weapons: Winning the fight, but losing the war for reproduction on a changing battlefield.

What conditions favor the evolution of large animal weapons? In the Japanese rhinoceros beetle, Trypoxylus dichotomus, del Sol et al. found that selection favors large horns in populations where males compete over guardianship of scarce female feeding territories. However, in other populations, an abundance of female feeding territories reduces the chance of mating success for these guarding males, leading to the evolution of relatively shorter horn sizes. This finding illustrates that female habitat and resource use have the potential to influence evolution of male weapon size through sexual selection.