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Although sexual selection through female choice explains exaggerated male ornaments in many species, the evolution of the multicomponent nature of most sexual displays remains poorly understood. Theoretical models suggest that handicap signaling should converge on a single most informative quality indicator, whereas additional signals are more likely to be(More)
Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous(More)
Agonistic carotenoid signalling in male red-collared widowbirds: aggression related to the colour signal of both the territory owner and model intruder Carotenoid colour displays are widely assumed to be honest indicators of individual health or quality, primarily in mate attraction. Here we show that sexually dimorphic carotenoid ornamentation functions as(More)
In breeding plumage, the African male red-shouldered widowbirds (Euplectes axillaris) are black except for red carotenoid-based epaulets ('shoulder patches'), similar to the well-studied American red-winged blackbirds (Agelaius phoeniceus). To experimentally test the signal function of the red epaulets in male red-shouldered widowbirds, we manipulated(More)
Recent sexual selection studies on the evolution of bird colouration have mainly focused on signals with a high level of condition-dependent variation, with much less attention given to colour traits whose expression is genetically controlled. Here, we experimentally tested the relative importance of a genetic colour polymorphism in determining male(More)
Many birds display carotenoid-based ornaments, which are typically considered to be honest indicators of individual health and condition. Experimental work on male red-shouldered widowbirds, Euplectes axillaris, has demonstrated a function of the carotenoid-based epaulettes in male contests and territory acquisition. Using two experiments, we investigated(More)
Sperm morphometry (i.e., size and shape) and function are important determinants of male reproductive success and are thought to be under stabilizing selection. However, recent studies suggest that sperm morphometry can be a phenotypically plastic trait, which can be adjusted to varying conditions. We tested whether different behavioral strategies in(More)
Individuals in socially monogamous species may participate in copulations outside of the pair bond, resulting in extra-pair offspring. Although males benefit from such extra-pair behavior if they produce more offspring, the adaptive function of infidelity to females remains elusive. Here we show that female participation in extra-pair copulations, combined(More)
In socially monogamous animals, mate choice is constrained by the availability of unpaired individuals in the local population. Here, we experimentally investigate the physiological stress endured by a female (the choosy sex) when pairing with a non-preferred social partner. In two experimental contexts, female Gouldian finches (Erythrura gouldiae) socially(More)
Evolutionary theory suggests that alternative colour morphs (i.e. genetically controlled phenotypes) may derive similar fitness under frequency-dependent selection. Here we experimentally demonstrate opposing effects of frequency-dependent social environments on plasma hormone levels (testosterone and corticosterone) and immune function between red- and(More)