Comparative evidence for sexual selection on nest weave pattern in weaverbirds

In most animals, nests primarily aim to protect offspring, and are presumably shaped by nat- ural selection. In some species, however, nests are conspicuous and elaborate, thereby visible to predators. One hypothesis to explain this apparent paradox is that nests could also evolve through sexual selection. Here, we tested this hypothesis by studying nest weaves across the weaver family (Aves: Ploceidae). We hypothesized that scale-invariance, a measure of vi- sual regularity of the weave, reflects the quality of the nest builder or activates pre-existing preferences exploiting a sensory bias in the receiver. We predicted a link between weave scale- invariance and two proxies of the intensity of sexual selection: mating system and sexual size dimorphism. Our results reveal that species under stronger sexual selection produce more scale-invariant weaves. These results suggest a previously unnoticed sexually selected signal associated with the evolution of some of the most spectacular constructions observed in the animal kingdom.