A group of dung beetle species that sprout horns like tiny elk, rhinos, or sci-fi invaders often face trade-offs between horn and testes sizes, say researchers.
Among the 2,000 species of Onthophagus dung beetles, males sport various styles of swooping prongs, with which they wrestle other males for access to females. "That's like producing another leg and wearing it around on your head for the rest of your life," says Douglas J. Emlen of the University of Montana in Missoula. His earlier experiments showed that as an individual beetle develops horns, they steal resources from other organs, leading to smaller eyes, antennae, or wings.
To test for trade-offs between horns and testes, Emlen and Leigh W. Simmons of the University of Western Australia in Crawley worked with