Impacts of mate quality on female intrasexual aggression in two sisterMalurusfairywren species

Abstract

AbstractLay summaryResearch on elaborate animal coloration overwhelmingly focuses on how males dress to impress potential mates or how color wards off potential rivals. In reality, female animals do this too, but it is less clear how competitive behavior varies among females that are pair-bonded with the prettiest males. In two closely-related songbird species, we did not find evidence that behavior varies in this context, showcasing how coloration may not be the most important variable females consider.While the impacts of male phenotypic quality on female mating decisions are well-studied, less is known about how male attributes may influence female aggressive behavior. To address this, we evaluated the degree to which females mated to more attractive males may behave more aggressively toward simulated female rivals, as might be predicted if intrasexual competition exists over access to mates. We studied two sister taxa of fairywren (Maluridae) with distinct life-history strategies: white-shouldered fairywrens (Malurus alboscapulatus moretoni) in Papua New Guinea, a species with year-round territoriality and female-limited plumage polymorphisms, and red-backed fairywrens (M. melanocephalus melanocephalus) in temperate Australia, a species with seasonal breeding and one in which females do not exhibit any plumage ornamentation. We characterized male quality by assessing the plumage coloration alongside three morphological characteristics that are known to be important inMalurusfairywrens: body mass, cloacal protuberance volume, and tail length. We quantified female aggression using mirror image stimulations, finding that female white-shouldered fairywrens were more aggressive on average than female red-backed fairywrens. There was a non-significant tendency for more aggressive white-shouldered fairywren females to have heavier mates with longer tails, but male phenotype did not predict female behavior in the red-backed fairywrens. Overall, our results are consistent with the idea that variation in mating system and life-history help shape female aggressive behaviors between divergent species. In socially monogamous species that form long, multiyear bonds with their mates, phenotypic quality may not be the best predictor of mate choice as has historically been emphasized.