Female aggression and male phenotype in two Malurus fairywrens
Description
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 tested this idea in two sister taxa of fairywren (Maluridae) with markedly distinct life-history strategy and mating system: 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 of the crown and scapular feather tracts via reflectance spectrometry alongside three morphological characteristics that are likely important in Malurus fairywrens: body mass, cloacal protuberance volume, and tail length. We quantified female aggression via the use of mirror image stimulations: assays which assess an individual’s reaction to a rival conspecific of equivalent visual quality, as represented by their own reflection. We found that female white-shouldered fairywrens were more aggressive during mirror assays 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 no indication that attributes of male phenotype predicted female aggression in the red-backed fairywrens. Included in this depository are: (1) R source code (including R studio project) (2) Raw spectral readings for feathers collected from white-shouldered and red-backed fairywrens (3) Behavioral responses to mirror image stimulation assays